7th Generation Two Microphone ENR Technology for Headsets

7th Generation Two Microphone ENR Technology for Headsets
CVC®
7th Generation Two Microphone ENR
Technology for Headsets
Tuning Guide
Issue 1
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Document History
Date
History
1
19 APR 12
Original publication of this document
Contacts
General information
Information on this product
Customer support for this product
More detail on compliance and standards
Help with this document
© Cambridge Silicon Radio Limited 2012
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www.csr.com
[email protected]
www.csrsupport.com
[email protected]
[email protected]
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Revision
Trademarks, Patents and Licences
Bluetooth® and the Bluetooth logos are trademarks owned by Bluetooth SIG, Inc. and licensed to CSR.
Other products, services and names used in this document may have been trademarked by their respective
owners.
The publication of this information does not imply that any licence is granted under any patent or other rights
owned by CSR plc or its affiliates.
CSR reserves the right to make technical changes to its products as part of its development programme.
While every care has been taken to ensure the accuracy of the contents of this document, CSR cannot accept
responsibility for any errors.
Life Support Policy and Use in Safety-critical Compliance
CSR’s products are not authorised for use in life-support or safety-critical applications. Use in such applications is
done at the sole discretion of the customer. CSR will not warrant the use of its devices in such applications.
Performance and Conformance
Refer to www.csrsupport.com for compliance and conformance to standards information.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Unless otherwise stated, words and logos marked with ™ or ® are trademarks registered or owned by CSR plc
and/or its affiliates.
Contents
© Cambridge Silicon Radio Limited 2012
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Document History.................................................................................................................................................... 2
Contacts .................................................................................................................................................................. 2
Trademarks, Patents and Licences ......................................................................................................................... 3
Life Support Policy and Use in Safety-critical Compliance ...................................................................................... 3
Performance and Conformance .............................................................................................................................. 3
Contents .................................................................................................................................................................. 4
Tables, Figures and Equations................................................................................................................................ 5
1.
Introduction................................................................................................................................................... 6
1.1. General ..................................................................................................................................................... 6
1.2. Software Versions Supported ................................................................................................................... 6
1.3. 7th Generation New Features ................................................................................................................... 7
2.
Prerequisites ................................................................................................................................................ 8
2.1. SPI Communication Protocol Drivers ........................................................................................................ 8
2.2. Hardware Interfaces.................................................................................................................................. 8
2.3. Parameter Manager Tool and User Guide ................................................................................................ 8
3.
Tuning Overview ........................................................................................................................................ 11
3.1. Tuning Stages Description ...................................................................................................................... 12
3.2. Tuning Flowchart .................................................................................................................................... 12
4.
Tuning Preparation ..................................................................................................................................... 14
4.1. Before You Start Tuning ......................................................................................................................... 14
4.2. Headsets Design Guidance and SPI Access .......................................................................................... 14
4.3. Phone Models and Network Types ......................................................................................................... 15
4.4. Tuning Environment ................................................................................................................................ 16
4.5. Level Speech Phrase .............................................................................................................................. 16
5.
Instrumentation........................................................................................................................................... 17
5.1. SPL Meter ............................................................................................................................................... 17
5.2. Head and Torso Simulator ...................................................................................................................... 17
6.
Tuning Preparation Checklist ..................................................................................................................... 18
7.
Tuning Procedures ..................................................................................................................................... 19
7.1. Objective Measurement .......................................................................................................................... 19
7.2. Receive Path Tuning............................................................................................................................... 19
7.3. Send Path Tuning ................................................................................................................................... 22
8.
Fine Tuning ................................................................................................................................................ 31
8.1. Receive Path Fine Tuning....................................................................................................................... 31
8.2. Send Path Fine Tuning ........................................................................................................................... 33
9.
Advanced Tuning ....................................................................................................................................... 35
9.1. Advanced Tuning Features ..................................................................................................................... 35
Document References .......................................................................................................................................... 44
Terms and Definitions ........................................................................................................................................... 44
Tables, Figures and Equations
Figure 2.1: CSR SDK Software Setup Window with Driver Installation Option Selected......................................... 8
Figure 2.2: Accessing the Headset Parameter Manager from the UFE .................................................................. 9
Figure 2.3: Parameter Manager Window, Static Mode .......................................................................................... 10
Figure 2.4: Parameter Manager Window, Monitoring Mode .................................................................................. 10
Figure 3.1: CVC HS Overview in the Parameter Manager .................................................................................... 11
Figure 3.2: The Six CVC HS Tuning Stages ......................................................................................................... 11
Figure 3.3: Tuning Flowchart ................................................................................................................................ 13
Figure 4.1: DEV-SYS-MONOHS-1A Extension Headset ...................................................................................... 15
Figure 4.2: A Recorded Waveform of the English Phrase “one two three four five” .............................................. 16
Figure 7.1: Receive Path Processing Blocks ........................................................................................................ 19
Figure 7.2: Packet Loss Concealment Settings Window ....................................................................................... 20
Figure 7.3: Receive Automatic Gain Control Settings, Default .............................................................................. 20
Figure 7.4: Mono Headset Configuration Tool, Audio Gains ................................................................................. 21
Figure 7.5: Receive Path Noise Suppression Settings Window ............................................................................ 22
Figure 7.6: Send Path Processing Block Diagram ................................................................................................ 23
Figure 7.7: Microphone Gain Settings Window ..................................................................................................... 24
Figure 7.8: Send Automatic Gain Control Settings Window .................................................................................. 25
Figure 7.9: Wind Noise Reduction Settings Window ............................................................................................. 26
Figure 7.10: Send Path Noise Suppression Settings Window ............................................................................... 27
Figure 7.11: Acoustic Echo Cancellation Settings Window ................................................................................... 28
Figure 7.12: Low Volume Mode Threshold Operation ........................................................................................... 29
Figure 7.13: Comfort Noise Settings Window ....................................................................................................... 30
Figure 8.1: Hard Clipper Setting Window .............................................................................................................. 32
Figure 8.2: Auxiliary Stream Mix Setting Window.................................................................................................. 33
Figure 9.1: Noise- Dependent Volume Control Settings........................................................................................ 36
Figure 9.2: Adaptive Equalization Settings Window .............................................................................................. 37
Figure 9.3: Adaptive Equalisation Switching to Mid Noise Tier ............................................................................. 38
Figure 9.4: Adaptive Equalisation Switching to High Noise Tier ............................................................................ 39
Figure 9.5: Side Tone Generation Settings Window ............................................................................................ 43
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Table 1.1: Part Number Matrix ................................................................................................................................ 6
Table 5.1: Recommended Meter Settings ............................................................................................................. 17
1.
Introduction
A Windows PC-based configuration tool (Parameter Manager) that communicates with CSR’s BlueCore® IC,
simplifies the tuning process. This tool monitors audio signal statistics and can be used to adjust CVC HS audio
processing block parameters to achieve optimal audio performance.
1.1.
General
CVC software is a sophisticated application that allows users to compensate for environmental and acoustic
variables to improve a product’s sound quality performance. The CVC software tuning procedure is completed by
a series of acoustic and electro-acoustic tests and measurements performed in a specific sequence. The test
results are used to modify CVC software audio processing parameters. The main purpose of the CVC software
tuning procedure is to achieve an optimum level of headset sound quality.
The product developer may perform the CVC tuning process at several stages during the headset system’s
development cycle. Typically, a developer fabricates a prototype headset system that packages audio, power,
communication, and processing components. Tuning can begin when a prototype system is available. Final
tuning to verify optimal performance should be completed when the final production components and packaging
are available.
The CVC HS application includes default settings that can be used for its audio processing. These defaults may
require gains adjusting to compensate for variations in the hardware design, such as microphones and speakers.
1.2.
Software Versions Supported
This Tuning Guide covers the audio adjustments of CVC BCSW-CVC-HS-5-6-1 algorithms. The same audio
tuning procedure is recommended when the algorithm is used on the ICs listed in Table 1.1.
IC Supported
CVC Product Code
Version
SysID
NB (8k)
WB (16k)
CVC License Key Part
Number
CSR8670 or
BlueCore5Multimedia
BCSW-CVC-HS-5-6-1
B10A
Yes
Yes
BCSW-CVC-HS-2M-Fx
BCSW-CVC-HS-5-6-1
B10A
Yes
Yes
No key required for this ROM
based part.
(Flash)
CSR8640
(ROM)
Table 1.1: Part Number Matrix
Notes:
(1) CSR86xx ROM, CS8670 and BlueCore5-Multimedia flash ICs supports narrow band (NB) using CVSD
and includes wide band (16kHz sample rate) using modified sub band coding (mSBC).
(2) CSR8640 UFE installer is located at https://www.csrsupport.com/ for download.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
This document is designed for the headset manufacturers' audio developers and describes how to tune Clear
Voice Capture (CVC®) 2-mic Headset (HS) audio processing software running on CSR multimedia Integrated
circuits (IC).
1.3.
7th Generation New Features
This section lists improvements made since the previous release (BCSW-CVC-HS-5-5-1) that improve
performance and or affect the tuning process.
New/improved features include:

Now supports CVC Generation 7 features

Added Simple Speech Recognition (SSR) functionality

Optimised latency using 60 sample Frame Size

In the Dual Mic Signal Separation (DMSS) block, added parameter for Front Mic Bias and updated defaults

In the Automatic Gain Control (AGC) blocks, updated defaults

In the Acoustic Echo Cancelation (AEC) block, updated defaults

In the Comfort Noise (CNG) block, added parameter for noise Shape

In the Auxiliary Stream Mix, updated defaults
CSR recommends that product developers become familiar with the principles of acoustic performance and the
tuneable parameters supported by the Parameter Manager tool before starting to tune their devices.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
CVC’s 2-mic solution is in constant development, adding features and making improvements driven by the
market place.
2.
Prerequisites
2.1.
SPI Communication Protocol Drivers
The CSR ADK software includes the Serial Peripheral Interface (SPI) drivers required by the CVC HS Parameter
Manager tool.
Note:
The SPI connection does not work if the SPI device drivers are missing.
To ensure these drivers are installed during the ADK installation, check the Install the SPI device driver option.
See Figure 2.1.
Figure 2.1: CSR SDK Software Setup Window with Driver Installation Option Selected
2.2.
Hardware Interfaces
The Parameter Manager and PSTool require a serial peripheral interface (SPI) interface to communicate to the
target hardware. The headset under development must support a SPI interface to a PC in order to tune the CVC
software for a specific product.
2.3.
Parameter Manager Tool and User Guide
The Parameter Manager provides the following assistance to the tuning process:

A graphical user interface (GUI)

Displays live signal statistics

Allows parameters to be easily adjusted using the Windows interface

Makes changes to the tuning parameters storing them as PS Keys in the BlueCore Persistent Store
The BCSW-CVC-HS-5-6-1 CVC- HS Parameter Manager User Guide describes how to use the tool and explains
the CVC parameters, their configuration, valid parameter ranges and their number formats.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
This section describes the prerequisites for CVC headset tuning.
The Parameter Manager is accessible through the Universal Front End (UFE) Application. CSR provides a
Windows Installer application for ROM IC's and is included with the ADK.
For ROM ICs
By default the installer creates a subdirectory on the program files of the PC:
C:\Program Files\CSR\<Installer Name>
A corresponding Start Menu Folder and desktop icon can be chosen during the installation process.
Start -> All Programs -> <Installer Name>
2.3.2.
For Flash-Based ICs
By default the ADK installation creates a subdirectory on the root drive of the PC:
C:\<ADK Name>\Tools\UFE\CSR\UnviversalFrontEnd.exe
A corresponding Start Menu link is created during the installation process.
Start -> All Programs -> <ADK Name> -> Tools -> UniversalFrontEnd
The Headset Parameter Manager is accessible from the HTML Start Page of Universal Parameter Manager
application. See Figure 2.2
Figure 2.2: Accessing the Headset Parameter Manager from the UFE
Figure 2.3 shows the 2-mic Headset Parameter Manager window that appears when the application is started i.e
the application is connected and in the Static mode.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
2.3.1.
Figure 2.4 shows an example screenshot in Monitoring mode, i.e. providing live feedback and statistics as the
algorithm is running during an active call.
Figure 2.4: Parameter Manager Window, Monitoring Mode
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Figure 2.3: Parameter Manager Window, Static Mode
3.
Tuning Overview
Figure 3.1 shows the CVC processing blocks in the Parameter Manager window. The tuning process involves
adjusting each of these major processing blocks and setting the gains at each CVC interface point.
Figure 3.1: CVC HS Overview in the Parameter Manager
Figure 3.2 shows the six stages to the CVC HS tuning process:
TUNING
PREPARATION
OBJECTIVE
MEASUREMENT
(OPTIONAL)
RECEIVE
PATH
TUNING
SEND
PATH
TUNING
FINE
TUNING
ADVANCED
TUNING
(OPTIONAL)
Figure 3.2: The Six CVC HS Tuning Stages
Note:
Some stages may be unnecessary, if a specific CVC feature block is not being used in a particular design.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
This section describes the overall process of tuning the CVC HS audio processing subsystem and presents the
suggested sequence of the tuning process for CVC HS applications.
3.1.
Tuning Stages Description
Tuning Preparation: The process of preparing the test environment and setting up the test
equipment.
2.
Objective Measurement (optional): Makes use of a HATS system to characterise frequency
response, loudness rating, and distortion characteristics of the DUT.
3.
Receive Path Tuning: Focuses on tuning the Receive path processing blocks of the CVC HS
algorithm (PLC, Receive AGC, Speaker Gain, and Noise Suppression).
4.
Send Path Tuning: Focuses on tuning the Send path processing blocks of the CVC HS algorithm
(Microphone Gain, Noise Suppression, Wind Noise Reduction, Acoustic Echo Canceller, Send
AGC, and Comfort Noise).
5.
Fine-Tuning: The fifth stage at which minor adjustments are made to the processing blocks as
required (Clipper, EQ and so on).
6.
Advanced Tuning (optional): The final stage is adding/tuning the advanced feature processing
blocks.
Note:
Some of these features have been added as part of the 5th Generation CVC.
The following features may be enabled and tuned to enhance the audio performance. However, power
consumption will slightly increase as a result.
Enabling and tuning the following processing blocks should be made as required:

Adaptive EQ with Frequency Expansion

NDVC

Auxiliary Stream Mixer

Side Tone
See section 4 through section 10 for instructions on successfully completing the six tuning stages.
Notes:
Use a copy of the BCSW-CVC-HS-5-6-1 CVC- HS 2-mic Parameter Manager User Guide as a reference
during the tuning process. See the Document References section for document details.
CSR recommends that developers periodically save the best tuning settings to either the Persistent Store
(PS) memory or to a .psr file to revert to for later use if required.
3.2.
Tuning Flowchart
Figure 3.3 shows a suggested procedure to step through the tuning process. Sections 7,8 and 9 describe the
steps in more detail.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
1.
Fine Tuning Process
(See Section 8)
Start CVC HS Tuning
CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Receive Path Tuning
(See Section 7.2)
Load Default or Preset
Parameters (Sect. 7.2.1)
Receive Path Fine Tuning
Refine Minimum Loudness,
AGC, EQ, Clipper and Aux
Stream Mix
(See Sections 8.1.1 – 8.1.5)
Enable PLC
(See Sect. 7.2.2)
Send Path Fine Tuning
Refine EQ, AGC, DMSS, and
Noise Suppression
(See Sections 8.2.1 – 8.2.4)
Receive AGC
(See Sect. 7.2.3)
SPKR Gain
(See Sect. 7.2.4)
No
Noise Suppression
(See Sect. 7.2.5)
Satisfied with Audio
Performance?
Yes
Do you want
Advanced Audio
Features enabled?
Send Path Tuning
(See Section 7.3)
MIC Gain
(See Sect. 7.3.1)
No
Yes
Send AGC
(See Sect. 7.3.2)
NDVC
(See Sect. 9.1.1)
Wind Noise Reduction
(See Sect. 7.3.3)
Adaptive EQ
(See Sect. 9.1.2)
Dual Mic Signal Separation
(See Sect. 7.3.4)
Noise Suppression
(See Sect. 7.3.5)
Adaptive EQ with High
Frequency Emphasis or
Expansion
(See Sect. 9.1.3)
Acoustic Echo Canceller
(AEC)
(See Sect. 7.3.6)
Side-Tone
(See Sect. 9.1.4)
Comfort Noise
(See Sect. 7.3.7)
No
Satisfied with Audio
Performance?
Receive Signal Path
No
Yes
Send Signal Path
Satisfied with Audio
Performance?
Yes
End CVC Headset
Tuning Complete
Perform if needed
Figure 3.3: Tuning Flowchart
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4.
Tuning Preparation
Because each CVC software application has a unique acoustical, electrical, and mechanical environment in
which it functions, it is important to consider the environment in which it will be used and the factors that may
affect its performance.
4.1.
Before You Start Tuning
Before starting the tuning process, review the preparation information in this section and complete the Tuning
Preparation Checklist in section 6.
4.2.
Headsets Design Guidance and SPI Access
Before tuning headsets check that the headset has been manufactured to meet the CSR 2-Mic Headset Design
Guidelines described in 2-Mic Headset Design Guidelines.
A partial list of CSR recommendations is:
1.
The audio components and plastics are production-level or production-intended.
2.
The microphone arrangement and industrial design is consistent and within the CVC 2-mic design
limitations, as in the CSR DEV-SYS-MONOHS-1A extension type headset, i.e. with microphones inline with the mouth and properly separated. Recommended microphone separation distance is
30mm, with a tolerance of +170 mm and -10 mm.
Microphones are oriented orthogonal to each other. The microphone furthest from the mouth is
oriented to face outwards while the microphone nearest the mouth is oriented to face towards the
direction of the mouth. See Figure 4.1.Error! Reference source not found.Error! Reference
source not found. The device has SPI connectivity to a PC running the Parameter Manager
software available.
3.
The SPI breakout cabling does not obstruct or interfere with the headset’s microphone and receiver.
4.
Before testing, the headset’s battery is fully charged or has an external power source.
5.
The headset is paired to a mobile telephone supporting the Bluetooth Headset profiles.
6.
During testing, the headset is worn in the way it was designed to be. For example, if the headset is
an inner-ear type, it should be worn in this fashion.
7.
Make a short call with the default CVC HS parameters to check the operation before making any
adjustments.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
This version of the CVC software is designed for use with Headsets that have two microphone input channels.
Omni-directional Microphone
placement example
CSR Reference Design
DEV-SYS-MONOHS-1A
Microphone Spacing
30 mm +/- 10 mm
Secondary Rear
Microphone
Primary Front
Microphone
Figure 4.1: DEV-SYS-MONOHS-1A Extension Headset
4.3.
Phone Models and Network Types
You must understand the general performance of the phones that the headset product will support for these
reasons:



Phone models and local networks vary and affect the sound quality, while also affecting the headset
product’s performance.
Phones or chipsets may have industry-known issues such as only supporting partial duplex.
Local networks may have known noise suppression characteristics that cause fluctuations in the background
noise during a call.
Because network types and phone models vary in the Receive SCO Audio level, CSR recommends performing
initial tuning using the mobile phone and network that has the lowest Receive SCO Audio level and has no known
or discovered audio issues. To check the lowest Receive SCO Audio level, monitor the Peak SCO In statistic.
When the initial tuning is complete and validated, test other phones to verify the performance (further fine
adjustments may be required based on test results).
Perform tuning during cellular off-peak hours (10:00-16:00 and 19:00-07:00). This limits the amount of cellular
network effects (such as aggressive routing schemes, comfort noise generation, bandwidth limiting, and
compression) that may influence telephone sound quality.
CSR recommends using a GSM mobile telephone as the primary tuning phone. Upon completing tuning, check
the headset sound quality with a CDMA mobile phone for similar results. In CDMA-dominant countries, it is
adequate to tune using only a CDMA phone.
While on a headset call, it is normal to hear a buzz noise while tuning with a GSM mobile. You may need to move
the GSM mobile to another location so that the buzz noise does not couple to the test hardware, especially the
headset microphone(s) and speakers.
Note:
Moving the Bluetooth-paired phone to different locations may degrade the Bluetooth link between the phone
and the headset kit. This will affect the sound quality of the headset call.
For best interoperability between the phone and headset product, CSR recommends the Bluetooth Headset
Profile (HSP) with an implementation of AT commands for turning off the mobile phone’s noise reduction and
echo cancellation processing.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Example:
CL
4.4.
Tuning Environment
During the tuning process, the near-end (headset) and far-end (landside) subjects must be acoustically isolated.
Avoid the far-end subject’s direct speech at the near-end microphone to mitigate undesired echo and acoustic
feedback.
Note:
To help minimise sound exposure that may be potentially damaging, CSR recommends using earplugs when
testing in moderate to high sound pressure levels.
4.5.
Level Speech Phrase
To obtain a proper signal for measuring speech levels in the processor, CSR recommends using a steady speech
pattern. For example, repeat the English phrase “one two three four five” or “a b c d e” at a quick rate, with no
pause between each word, for the specified measurement period. This technique provides a reasonably stable
speech signal and reduces the dependency on sophisticated test equipment.
Note:
For more precise tuning, a laboratory-based test is required. CSR-Detroit can carry out laboratory-based
tests on request.
When the near-end subject speaks the level speech phrase, measurement of the Sound Pressure Level should be
approximately 25mm from the near end subject’s mouth.
Figure 4.2 shows a recorded waveform of the near-end subject’s voice while speaking the test phrase “one two
three four five” twice.
Figure 4.2: A Recorded Waveform of the English Phrase “one two three four five”
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
The tuning process requires that the tuning environment is a controlled space that imitates, or is able to simulate,
the operating environment of the final product. For headsets, the tuning environment is a quiet environment with
low reverberation (such as an anechoic chamber) and a noisy environment (public space, car cabin, and so on).
Instrumentation
5.1.
SPL Meter
For measuring Sound Pressure Level (SPL), CSR recommends using a high-quality digital sound meter, such as
a Bruel & Kjaer (B&K) Type 2239 Sound Level Meter or equivalent. Table 5.1 lists the recommended sound level
meter measurements and meter settings.
Meter Measurements
Meter Settings
Measurement Type
Sound Pressure Level
Weighting
C-weighted (according to IEC-179)
Filter
Random incidence
Detector Type
RMS
Averaging
Fast
Units
dBSPL
Table 5.1: Recommended Meter Settings
5.2.
Head and Torso Simulator
CSR also recommends the use of a Head and Torso Simulator (HATS) capable of electro-acoustic
measurements on telephones as in ITU-T recommendations. The HATS system should be capable of testing
send/receive frequency response, send/receive loudness rating, and receive-path THD+N.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
5.
6.
Tuning Preparation Checklist
Check


Break-out SPI wiring does not obstruct or interfere with the headset microphone and
receiver


Fully charged headset battery or external power source


Paired to a mobile phone

GSM Mobile Phone with Bluetooth Headset Profile

Fully charged phone battery or external power source


Noise Suppression and Echo Cancellation disabled on the phone


Mobile phone in close proximity to the headset


No GSM buzz noise coupling on the headset

Control of Noise Environment

Near-end and Far-end subjects are acoustically separated


Low network traffic test time


Set the SPL Meter to the settings listed in section 233H5.1


Calibrate the Sound Pressure Level Meter to a 1 kHz 94 db re 20μPa sine tone


Ensure all cables and power supplies are in proper working order


Parameter Manager tool connected to the Headset system

Accessories

Ear Plugs

Hardware

Far-end (landside) subject


Near-end (headset) subject

Documentation

CVC 2-mic Headset Design Guidelines


Parameter Manager User Guide

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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Production or Production-intended Audio Components and Plastics

SPI communication to PC
Tuning Procedures
7.1.
Objective Measurement
After completing the tuning preparation process, the headset device can be acoustically characterised using an
objective telephone sound quality test system. This system normally uses HATS, a PC audio interface,
professional-grade measurement microphones, reference phone system, and measurement software containing
standardised test methods (such as ITU-T, TIA/EIA, and so on).
These objective telephone sound quality test systems are useful to perform future tuning activities:



Send/Receive frequency response (TIA/EIA 810-A): Helpful for tuning Receive EQ and Send EQ.
Send/Receive loudness rating (ITU-T P.79, ITU-T P.50): Helpful for tuning SPKR Gain, MIC Gain, and Send
Gain.
Send/Receive Distortion (THD/THD+N): Helpful for tuning the MIC Gain to a level limiting distortion and
setting the SPKR Gain to a level limiting distortion.
7.2.
Receive Path Tuning
Figure 7.1 shows the CVC HS Receive Path processing blocks.
Figure 7.1: Receive Path Processing Blocks
Note:
Repeat all tuning measurements at least twice.
7.2.1.
Load Preset Parameters
If the headset is being tuned for the first time, begin tuning with the default parameters provided with the CVC HS
release. The defaults can be loaded using the Parameter Manager application by selecting Use Default
Parameters on the Parameters menu. When the defaults have been loaded, you want to Bypass the advanced
processing blocks to simplify tuning. Bypass Adaptive EQ, Clipper and NDVC.
Note:
Advanced processing blocks: Adaptive EQ, Clipper and NDVC should be bypassed at this stage in the
tuning process.
Alternately, if you have previously tuned the headset and have saved the parameters, you can preload the saved
parameters and continue with the tuning process. The loading of saved parameters is described in the
Parameters Manager integrated documentation. Click the Quick Start link on Parameter Manager Documentation
opening window (home page) and read the Managing Parameter Settings and PS Key section.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
7.
7.2.2.
Packet Loss Concealment
Figure 7.2: Packet Loss Concealment Settings Window
7.2.3.
Receive AGC
The Receive Automatic Gain Control (AGC) automatically adjusts the receive path Receive SCO signal to a
specific level determined by the AGC Target Level parameter. This parameter compensates for variance in
Receive SCO signal levels. By default, the AGC Target Level is -20 db (RMS), and needs no additional tuning. If
additional fine tuning is required, see section 8.1.2.
Figure 7.3: Receive Automatic Gain Control Settings, Default
Note:
It is possible to bypass the Receive AGC by selecting Bypass Gain Control. CSR does not recommend
bypassing the Receive AGC.
7.2.4.
SPKR Gain
Tuning the speaker involves determining the maximum receiver volume that the headset supports. As the
headset’s volume increases, the acoustic coupling between the receiver and the microphone increases. A large
amount of acoustic coupling causes echo, which worsens when either the microphone or loudspeaker distorts.
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The Packet Loss Concealment block improves the receive path audio quality only in the presence of bit and
packet errors within the Bluetooth link by using a variety of techniques such as pitch based waveform
substitution. It is suggested to always leave the Packet Loss Concealment enabled to achieve the best audio
quality. You can check the Bypass Packet Loss Concealment to disable module if required. See Figure 7.2.
To tune the SPKR GAIN:
1.
Initiate a headset call.
2.
The far-end subject speaks the level speech phrase.
3.
The near-end subject measures or listens to the receiver volume.
4.
The near-end subject adjusts the loudspeaker volume by clicking the SPKR GAIN block, selecting
Temporarily override DAC and adjusting the SPKR Gain to the highest level that does not cause
distortion and passes objective and subjective loudness judgment.
5.
If there is distortion:
6.
5.1.
The near-end subject lowers the SPKR Gain or enables and adjusts the Clipper:
5.2.
The near-end subject adjusts the Clip Point until distortion is no longer heard.
5.3.
Optional: The near-end subject adjusts the Boost so that the desired receiver loudness is
maintained.
Using the Mono Headset Configuration Tool, select the Audio Gains tab to configure the required
number of volume steps and set the maximum volume.
Figure 7.4: Mono Headset Configuration Tool, Audio Gains
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Distortion cannot be eliminated, but efforts must be made to minimize it to an acceptable level. The use of better
quality loudspeakers, amplifiers, microphones, leak-tolerant packaging or improved acoustic separation of the
microphone and receiver help to reduce echo and distortion.
7.2.5.
Receive Noise Suppression
To tune for Noise Suppression:
1.
Initiate a headset call.
2.
The far-end subject introduces background noise into the testing environment.
3.
The far-end subject speaks a test phrase or a normal conversational phrase, continually.
4.
Under different noise conditions, the near-end subjectively evaluates the noise level and its quality
with and without far-end speech.
5.
Increase the HFK Aggressiveness for more noise suppression (at the cost of voice quality).
Decrease the HFK Aggressiveness for less noise suppression.
Notes:
The far-end subject should avoid using the level speech phrase while tuning the HFK Aggressiveness.
Normal conversational speech or phonetically-balanced phrases and passages are better for judging speech
intelligibility in the presence of noise.
High Quality Mode is checked (enabled) by default. This does not effect the noise suppression but provides
improved speech quality. If un-checked MIPS will be slightly reduced, but the voice quality will slightly
degrade.
Figure 7.5: Receive Path Noise Suppression Settings Window
7.3.
Send Path Tuning
Figure 7.6 shows the CVC software send path processing blocks. The send path processes speech, echo and
noise entering the headset microphones. The echo signal is the result of acoustic coupling from the loudspeaker
to the Send In microphones.
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The HFK Aggressiveness parameter is a primary tuning parameter which controls the amount of noise
suppression that is applied to the receive signal. Setting this parameter to 80% suppresses ~ 6 db of noise
(recommendation) and 100% suppresses up to 20 db of noise. However the receive signal has been processed
by the cellular network, and transmitted over Bluetooth so to avoid over processing the voice, the aggressiveness
should be set conservatively.
7.3.1.
MIC Gain
The MIC Gain is an analogue and a digital gain stage that boosts or reduces the signal picked up by the
microphone. If the microphone is low-level (microphone level), the integrated 24.0 db Pre-amp can be applied to
boost the signal to line level. Figure 7.7 shows a screenshot of the Mic Gain window.
To tune the MIC Gain (HFK Mode):
1.
Initiate a headset call.
2.
The near-end subject speaks the level speech phrase at approximately 90 db SPL(C) measured
25mm from the speaker’s mouth.
3.
The near-end adjusts the Primary Mic (Left) Gain and Enable 24.0 dB Pre-Amp (if required) so that
the Peak Mic statistic reads no more than -15 dbFS. Once set, apply the same Gain value and PreAmp setting to the Secondary Mic (Right).
4.
Since both microphones have similar characteristics, the Secondary Mic should have slightly lower
Peak Mic statistic readings than the Primary Mic.
If this is not the case, check the noise floor of the microphones.
To check noise floor, place the headset in a low stationary noise (i.e. white, pink or brown)
environment (Peak Mic statistics should report -30 to -50 dbFS). The two microphone Peak Mic
statistics should be within +/- 3 dbFS of each other. If not, compensate by adjusting the Secondary
Mic Gain and Enable 24.0 db Pre-Amp.
If changes are made, the speech levels should now be re-verified. If the secondary mic speech Peak
Mic statistic exceed the primary, then something is potentially wrong and the microphones may
need replacing or an alternate hardware design may need to be explored.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Figure 7.6: Send Path Processing Block Diagram
The near-end subject adjusts the headset receiver volume to the maximum, by increasing the gain
of the loudspeaker through manual volume controls. The far-end subject speaks short bursts of
speech (for example, “one”, “two”, “hello”, “ok”, “check”, “echo”, and so on) and checks for echo at
the far-end.
6.
If there is echo present at the far-end, the near-end subject decreases the Mic Gain levels equally.
Re-check for far-end echo.
Figure 7.7: Microphone Gain Settings Window
7.3.2.
Send AGC
The Send AGC automatically adjusts the send path send out signal to a specific level determined by the AGC
Target parameter. This parameter compensates for variance in the send out signal levels.
By default, the AGC Target is -20 db (RMS) and needs no additional tuning.
Note:
The Send AGC Target level is the level that the automatic gain control will attempt to reach when modifying
the send signal.
To tune the AGC Target Level (for headsets without a close-coupled microphone and speaker):
1.
Initiate a headset call.
2.
The near-end subject places the primary headset microphone at the closest specified operating
distance from the near-end subject.
3.
Next, the near-end subject speaks the level speech phrase at approximately 90 db SPL(C)
Weighted Fast, measured 25 mm from the speaker’s mouth.
4.
The near-end subject adjusts the AGC Target Level to achieve the required listening level at the farend. Ensure the speech is not clipping by monitoring the Send Out Peak statistic, avoid saturation.
Typically, the Send AGC should not be raised above -3 db target full scale (to allow for overshoot),
processing in the event of saturation or clipping.
5.
The Maximum Gain that can be applied to the signal can also be limited.
6.
The Compression Ratio can also be specified to suit the needs of the application.
7.
Make sure that the far-end subject never hears clipped or saturated voices.
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5.
Note:
The Send AGC has two statistics located directly below the Send AGC tuning block which are visible while in
monitoring mode to aid in the tuning process. These two statistics are the Send AGC Applied gain and the
Active Speech Level:
7.3.3.

Applied Gain: The App Gain statistic indicates how much gain the Send AGC is actively
applying to the input signal. It also shows how the Send AGC reacts to changes in speech
levels.

Active Speech Level: The Active Spch statistic indicates the input level for the active
portion of the speech signal as determined by CVC. Together the Active Speech Level and
the Applied Gain are used by CVC to check if the output level of the Send AGC is near the
Send AGC Target Level.
Wind Noise Reduction
This section describes areas to fine tune on the Wind Noise Reduction (WNR) settings window.
To Tune for WNR:
1.
The near-end subject continually repeats a test phrase or a normal conversational phrase.
2.
Set the Tier 1 Aggressiveness to 100% to begin tuning WNR (Wind Noise Reduction) and Bypass
Gain Control on the Send AGC.
3.
The near-end subject continually repeats a test phrase or a normal conversational phrase.
4.
While the test phrase is continually running, monitor the WNR Gain: x.xx statistic. It may be helpful to
use the Log Window to record the WNR Gain variance. After observing (or recording) the WNR Gain
statistic for about 20 seconds set the Wind Threshold below the lowest WNR Gain value. This
adjustment ensures WNR processing does not affect quiet speech.
5.
The near-end subject slowly adds wind using a controlled source (i.e. fan), attempting to maintain a
constant wind speed. Only add enough wind to determine when the WNR should start cleaning the
audio. To listen to the audio without the influence of the WNR, you can temporarily check the
Bypass WNR to determine the lowest wind speed. Once set, uncheck the Bypass WNR.
6.
Maintaining a constant wind speed, the NEAR END subject should add speech occasionally and
evaluates speech quality.
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Figure 7.8: Send Automatic Gain Control Settings Window
While combining the speech and wind, monitor the WNR Power: x.xx statistic. It may be helpful to
use the Log window to record the WNR Pwr variance. After observing the WNR Pwr statistic for
about 20 seconds set the Power Threshold below the lowest WNR Pwr value. This adjustment sets the
trigger point when WNR detects wind and applies processing.
8.
When the Wind Threshold and Power Threshold have been set, you can lower the Tier 1
Aggressiveness if you want less wind noise reduction, otherwise leave at 100%.
Note:
Increasing Tier 1 Aggressiveness, decreasing Power Threshold, and/or increasing Wind Threshold results in
more aggressive wind noise reduction.
9.
In Monitoring Mode, the WNR Gain is the value that is compared to the Wind Threshold setting when
determining if wind is detected. In some situations, it may be valuable to adjust Low Bin Index
(lowering increases likelihood of wind detection) and increasing Bin Count (typically remaining under
16).
Note:
Changes to these two parameters effect the calculations that report the WNR Gain and WNR Pwr statistics. If
you have modified one or both, repeat steps 4 through 7.
10.
Re-enable (i.e. un-check the Bypass Gain Control) the Send AGC.
Figure 7.9: Wind Noise Reduction Settings Window
7.3.4.
Dual Mic Signal Separation
This section describes areas to fine tune on the Dual Mic Signal Separation (DMSS) settings window.
To tune for DMSS:
1.
Initiate a headset call.
2.
Based on the headset to be tuned, adjust Front Mic to Mouth Distance and Mic Separation Distance (if
necessary).
3.
The near-end subject introduces background noise into the testing environment.
4.
The near-end subject speaks a test phrase or a normal conversational phrase, continually.
5.
Under different noise conditions, the far-end subjectively evaluates the noise level and its quality
with and without near-end speech.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
7.
6.
Send Noise Suppression
The HFK Aggressiveness parameter is a primary tuning parameter which controls the amount of noise
suppression that is applied to the send signal. Setting this parameter to 100% suppresses up to 20 db of noise.
To tune for Noise Suppression:
1.
Initiate a headset call.
2.
The near-end subject speaks a test phrase or a normal conversational phrase, continually.
3.
The near-end subject introduces background noise into the testing environment.
4.
Under different noise conditions, the far-end subjectively evaluates the noise level and its quality
with and without near-end speech.
5.
Increase the HFK Aggressiveness for more noise suppression (at the cost of voice quality).
Decrease the HFK Aggressiveness for less noise suppression.
Note:
The near-end subject should avoid using the level speech phrase while tuning the HFK Aggressiveness.
Normal conversational speech or phonetically-balanced phrases and passages are better for judging speech
intelligibility in the presence of noise.
Figure 7.10: Send Path Noise Suppression Settings Window
7.3.6.
Acoustic Echo Canceller
This section describes areas to fine tune on the Acoustic Echo Cancellation (AEC) settings window.
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7.3.5.
Increase the DMSS Aggressiveness for more noise suppression (at the cost of voice quality).
Decrease the DMSS Aggressiveness for less noise suppression.
7.3.6.1.
Acoustic Echo Cancellation Settings Fields Description

Bypass Acoustic Echo Cancellation: Check this option when echo cancellation is not required. If
bypassed, you can skip rest of this section.

Bypass Residual Echo Reduction: The Bypass Residual Echo Reduction option enables or disables
additional echo cancellation built into the AEC. Its purpose is to reduce the subtle non-linearity’s
that could exist after the primary adaptive filter. It is enabled by default. CSR recommends the
Residual Echo Reduction feature be enabled, to achieve the best echo cancellation performance.

Reuse Primary Filter: Under normal conditions, the filter converges to the required level so that
echo is reduced. This option is selected when the AEC filter convergence is required to be as close
as possible to the optimal convergence value. Check this option when the echo coupling is high.
Selecting this option increases the DSP processing load.

Reference Delay: The Reference Delay compensates for any time delay of the send signal caused
by additional processing preceding the Acoustic Echo Canceller. This feature ensures that the AEC
triggers at the correct time. The default reference delay value is 0 ms.

Double Talk Aggressiveness: Double Talk Aggressiveness is used to adjust the amount of doubletalk signal that is heard at the far-end. Decrease the Double Talk Aggressiveness to hear less
double-talk signal at the far-end or increase the amount of echo cancellation. Increase the Double
Talk Aggressiveness to hear more double-talk signal or decrease the amount of echo cancellation.

Low Volume Mode Threshold: The Low Vol Mode Threshold feature saves headset battery power by
turning off the Acoustic Echo Canceller and Comfort Noise generator when the Speaker Gain is set
below a certain threshold. You determine the threshold by lowering the volume until no perceived
echo or an acceptable echo is heard. Figure 7.12 shows the Low Volume Mode Threshold
operation.
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Figure 7.11: Acoustic Echo Cancellation Settings Window
To tune the Acoustic Echo Canceller:
1.
Initiate a headset call, set the loudspeaker volume to maximum.
2.
The near-end subject sets the Low Vol Mode Threshold to minimum (-45 dbr, Table Value 0) and
uncheck the Reuse Primary Filter.
3.
The far-end subject speaks short bursts of speech (for example, “one”, “two”, “hello”, “ok”, “check”,
“echo”, and so on) and checks for echo at the far-end.
4.
If echo is heard than check the Reuse Primary Filter and repeat step 3. If no echo is heard, continue
and setup the low volume mode.
5.
To Fine Tune the Acoustic Echo Canceller
6.
To fine tune the AEC by setting the low volume mode threshold:
7.
Initiate a headset call.
8.
The near-end subject selects Bypass Acoustic Echo Cancellation.
9.
The far-end subject speaks short bursts of speech (for example, “one”, “two”, “hello”, “ok”, “check”,
“echo”, and so on) and checks for echo at the far-end.
10.
Starting at the maximum receiver volume (gain), adjust the near end receiver volume downward. At
each volume adjustment, repeat step 3. Continue until the echo at the far-end user cannot be heard
or the echo is low enough not to require the echo canceller software. Record this volume setting.
Note:
To adjust the volume you can use the Speaker Gain Setting block – check Temporary override DAC – and
choose a volume from the Gain Select drop list. When complete, uncheck the Temporary override DAC option.
11.
The near-end subject sets the Low Vol mode threshold to the speaker volume (gain) level
determined in step 4.
12.
The near-end subject removes the checkmark in the Bypass Acoustic Echo Cancellation check box.
13.
At each speaker gain level, the far-end subject checks for echo at the far-end.
Note:
The Bypass Residual Echo Reduction feature is used to enable or disable additional echo cancellation built
into the AEC. The echo reduction feature is enabled by default. CSR recommends that this feature remain
enabled.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Figure 7.12: Low Volume Mode Threshold Operation
7.3.7.
Comfort Noise
Figure 7.13: Comfort Noise Settings Window
To Tune the Comfort Noise Generator:
1.
Initiate a headset call.
2.
The near-end subject introduces steady background noise into the testing environment.
3.
The near-end and far-end subjects alternate speaking numbers and letters (for example, “1”, “A”,
“2”, “B”, “3”, “C”, and so on) with a 1-second pause between each number and/or letter.
4.
The far-end subject listens to any fluctuations in the noise floor during the alternating speech.
5.
If fluctuations are heard, increase or decrease the amount of comfort noise.
6.
The near-end subject bypasses the Comfort Noise generator.
7.
The far-end subject checks for a large decrease in background noise as the Comfort Noise
generator is bypassed.
8.
If there is a large decrease in background noise, the near-end subject decreases the Comfort Noise
generator gain.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
The Comfort Noise generator adds noise to the send signal to minimise noise floor fluctuations introduced by the
echo cancellation. The Comfort Noise generator has a single gain control.
8.
Fine Tuning
8.1.
Receive Path Fine Tuning
This section describes fine adjustments that can be made to the CVC headset receive path.
8.1.1.
Setting Minimum Speaker Gain Loudness
The speaker gain tuning to obtain the maximum loudness setting is described in section 9.1.1. Setting the
Minimum Loudness for the loudspeaker gain is similar to setting the Maximum Loudness.
To fine-tune the Minimum Loudness Level:
1.
Initiate a headset call.
2.
Adjust the phone volume to minimum.
3.
The far-end subject speaks the level speech phrase.
4.
The near-end subject measures or listens to the loudspeaker volume. Click on the SPKR GAIN
block, select the Temporarily Override DAC option, and adjust the gain to your required minimum
level.
5.
Place the SPKR GAIN value into the VM volume table using the Mono Headset Configuration Tool,
choose the Audio Gains tab to configure desired number of volume steps as well as minimum.
8.1.2.
Receive AGC
To tune the Receive AGC:
1.
Adjust the AGC Target Level to required value. The default is -20 dB, which provides a good dynamic
range with almost full-scale peak values.
2.
Adjust the Minimum Gain, which sets the low threshold level for the gain factor. The gain factor will
not fall below the Minimum Gain.
3.
Adjust the Maximum Gain, which sets the high threshold level for the gain factor. The gain factor will
not exceed above the maximum gain. The Minimum Gain and the Maximum Gain defines the
dynamic range of the gain factor of the AGC.
4.
Adjust the Compression Ratio, which defines the slope of the compression curve, above the target
level. The gain factor follows the compression curve above the Compression Threshold, while the
slope of gain curve below the Compression Threshold is unity.
8.1.3.
Receive EQ
The receive path has a parametric equaliser for enhancing audio quality. By default, the parametric equaliser is
set flat, but may be used to troubleshoot loudspeaker distortion at specific frequencies or to pass standard
measurements (ITU-T). If required, the receive EQ can be used for frequency shaping to fit an appropriate
response curve. The GUI allows the Receive EQ parameters to be graphically selected, see Headset Parameter
Manager Users Guide.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
When the CVC headset receive and send paths are tuned, minor parameter changes may be required to reach a
good performance level. Some products have unique acoustic designs or require special headset sound quality
requirements for the product. This section describes additional tuning instructions for fine tuning of CVC headset
processing modules.
8.1.4.
Clipper
Note:
The Clipper’s Boost setting decreases the dynamic range of the receive signal, which degrades speech
quality.
To tune the Clipper:
1.
Initiate a headset call.
2.
Adjust the headset volume to maximum.
3.
The far-end subject speaks the level speech phrase.
4.
The near-end subject listens for distortion in the headset receiver.
5.
The near-end subject adjusts the Clip Point until distortion is no longer heard.
6.
Optional: If the Clipper is enabled, the near-end subject can adjusts the Boost so that the required
receiver loudness is maintained. Any boost will be hard clipped at the Clip Point.
7.
Optional: If the Clipper is enabled, the near-end subject can adjust the Boost Clip Limit enforcing the
maximum digital limit allowed in the path prior to the DAC.
Figure 8.1: Hard Clipper Setting Window
8.1.5.
Auxiliary Stream Mix
This feature is always enabled and stream mixing only occurs during a stream mix event (e.g. tone play). It mixes
an auxiliary signal with the SCO input signal. The auxiliary signal could be tones or another source such as voice
prompts. The ratio of the mixture is controlled by using the slider controls to achieve the required balance on the
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The Clipper prevents the receive path signal from exceeding a specified maximum level (Clip Point). If the
dynamic range of the receive signal is large and causes receiver distortion, the Clipper can be used to limit this
distortion. First, a Clip Point is selected in the Clipper settings to achieve a receive signal limit. The optional Boost
adds compression to the clipped signal (such as a loudness boost).
receive out signal. Changing a stream mix using a slider will inversely control the other to maintain 100%
between the channels.
The auxiliary signal can be boosted by using the Auxiliary Gain parameter. The maximum limit on the auxiliary
gain is 24 dB.
Figure 8.2: Auxiliary Stream Mix Setting Window
8.2.
Send Path Fine Tuning
This section describes fine adjustments to the CVC Headset send path.
8.2.1.
Send EQ
The send path has a parametric equaliser for enhancing audio quality. Normally, the parametric equaliser is set
flat, but may be applied to the send path signal at specific frequencies or used to pass standard measurements
(ITU-T).
If required, the Send EQ can be used to perform some frequency shaping to fit a required response curve. The
graphical user interface allows the Send EQ parameters to be graphically selected, see
Headset BCSW-CVC-HS-5-6-1 CVC- HS Parameter Manager User Guide.
Gain should be minimised (unity) through the EQ to avoid saturation and distortion.
8.2.2.
Send AGC
To fine-tune the Send AGC:
1.
Adjust the AGC Target Level to required value. The default is -20 dB, which provides a good
dynamic range with almost full-scale value.
2.
Adjust the Minimum Gain, which sets the low threshold level for the gain factor. The gain factor will
not fall below the Minimum Gain.
3.
Adjust the Maximum Gain, which sets the high threshold level for the gain factor. The gain factor will
not exceed above the maximum gain. The Minimum Gain and the Maximum Gain defines the
dynamic range of the gain factor of the AGC.
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If the Decouple Gains is checked, the user may separately adjust the mix ratios of the SCO and Auxiliary Streams
but caution should be taken if the percentage sums >100% as saturation could occur.
4.
8.2.3.
Simple Speech Recognition (SSR Mode)
8.2.3.1.
Simple Speech Recognition (SSR) Aggressiveness
The secondary tuning parameter in the Noise Suppression block, SSR Aggressiveness, controls the amount of
noise suppression applied to the send signal during SSR mode. Setting this parameter to 100% suppresses up to
20 dB of noise. In the SSR mode, the CVC-enabled headset acts as a speech capture device used for voice
recognition applications. The SSR mode gain should be adjusted to the specific demands of the voice recognition
application.
CSR recommends using 95% SSR Aggressiveness as this provides a good balance of having superior noise
suppression with minimal voice distortion.
8.2.4.
Dual Mic Signal Separation (DMSS)
To fine-tune the DMSS:
1.
Select Bypass Mic Gain Differential Compensation if the Mic Separation Distance is greater than 50mm.
The greater the distance between microphones, the less impact MGDC will have.
CSR recommends leaving the MGDC active.
2.
Select Bypass Pre-Processing if the Mic Separation Distance is greater than 50mm. Pre-Processing
generally increases the rejection of noise from behind the headset user, and trading off noise
rejection from in front of the user.
3.
Choose a Post-Processing Control other than default if the Mic Separation Distance is greater than
50mm. A preset is already created for "Wide Mic". Other presets may be created by choosing
alternative tuning, typing into the Presets box, and selecting "Add".
4.
Select Wide Mic Mode if the Mic Separation Distance is greater than 50mm.
5.
Unselect Repeat Post Processing if the Mic separation Distance is greater than 50mm.
6.
Increase the Front Mic Bias to achieve more aggressive Noise Reduction.
7.
Increase the Step Size to achieve more aggressive Post Processing.
8.
Increase the Threshold to achieve more aggressive Post Processing.
9.
Increase the Control Bias to achieve less aggressive Post Processing.
10.
Select Bypass Residual Noise Reduction to limit the aggressiveness of the DMSS.
11.
Increase the SNR Bias to achieve less aggressive Residual Noise Reduction.
12.
Increase the SNR Transition to achieve more aggressive Residual Noise Reduction.
13.
Increase the Gain Adjustment to achieve more aggressive Residual Noise Reduction.
14.
On Threshold controls the point at which the Noise-Dependent Power Saving (NDPS) switches On.
Increase the On Threshold to switch NDPS On sooner (during times with more noise).
15.
Increase the OFF Threshold to switch NDPS Off later (during times with more noise). It is important to
keep some amount of separation (hysteresis) between the On and OFF settings.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Adjust the Compression Ratio, which defines the slope of the compression curve, above the target
level. The gain factor follows the compression curve above the Compression Threshold, while the
slope of gain curve below the Compression Threshold is unity.
Advanced Tuning
9.1.
Advanced Tuning Features
For headset products that offer adequate fidelity the user can enable advanced CVC features that include the
NDVC, AEQ and Side tone.
9.1.1.
Noise-Dependent Volume Control
The Noise-Dependent Volume Control (NDVC) should be tuned after the MIC Gain. See section 7.3.1 for
instructions on tuning the MIC Gain.
The NDVC automatically increases or decreases the loudspeaker volume depending on the level of noise in the
environment. The gain added from NDVC to the SPKR Gain should not exceed the maximum output level
determined in section 7.2.4.
To tune the NDVC:
1.
Initiate a headset call.
2.
Click on the NDVC processing block and remove the checkmark from the Bypass NDVC check box.
This enables the NDVC.
3.
Increase the noise floor inside the vehicle to the required level at which the NDVC should start to
adjust the volume (for example, driving at a speed of 20 mph).
4.
Monitor the Noise Level statistic and type this value in the Min noise level field.
5.
Increase the noise floor inside the vehicle to the required maximum level at which the NDVC should
remain turned on (for example, driving at a speed of 55 mph). Monitor the Noise Level statistic and
place this value in the Max noise level field.
6.
During the high noise condition, the near-end subject determines the maximum gain that the NDVC
can apply and enters this number in the Maximum NDVC Gain Limit field.
Notes:

The NDVC does not adjust the SPKR Gain over 0 dB. For example, if the SPKR Gain is -12 dB and the
Maximum NDVC Gain Limit is 15 dB, the NDVC does not apply more than 12 dB of gain. The maximum
loudness is limited to 0 dB under the highest noise condition.

The Total SPKR Gain = SPKR Gain + Maximum NDVC Gain Limit

The Total SPKR Gain is important when tuning the Send Path.
7.
Set the Hysteresis to a value between zero and one. Higher values reduce the NDVC sensitivity
when reacting to changes in the background noise and lower values increase the sensitivity. The
default value is 0.0 and should be changed.
8.
Adjust the Increasing Noise Attack Time Constant and Decreasing Noise Decay Time Constant to a
required level. High time constant values cause the NDVC to react more slowly to changes in the
background noise and lower values cause a quicker reaction.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
9.
NDVC Defaults Settings
NDVC Example Alternate Tune
Note:
Figure 9.1 shows the default settings. You must adjust the Max noise level and Min noise level for your
specific headset.
9.1.2.
Adaptive EQ (AEQ)
There are three systems available for the CSR68xx:
1.
Narrow Band plus High Frequency Emphasis: consists of AEQ (0 to ~3.5 kHz) plus the addition of
an Emphasis Band (~3.5 to 4 kHz).
2.
Narrow Band plus Frequency Expansion: consists of an AEQ (0 to ~3.5 kHz) plus the addition of
Expanded Bands (~3.5 to ~6.2kHz).
3.
Wide Band: consists of an AEQ (0 to 8 kHz).
When Adaptive Equalisation block is enabled, it improves the intelligibility of the receive path voice signal in the
presence of near end noise. It does this by altering the spectral shape of the receive path signal while
maintaining the overall power level. Both High Frequency Emphasis and Frequency Expansion are described in
section 9.1.3.
It has been empirically observed that consonants, which are dominantly high frequency based and much lower in
amplitude than vowels, significantly contribute to the intelligibility of the voice signal. In the presence of noise, the
lower amplitude consonants become masked by this noise. Therefore, by increasing the frequency components
that contribute to the consonants while in the presence of noise, the intelligibility can be improved.
In order to maintain a consistent amplitude level, the Adaptive Equalization block adaptively increases the high
frequencies relative to the middle frequencies while reducing low frequencies accordingly.
The adaptive equaliser also has the capability to compensate for variations in voice transmission channels, which
include far-end devices and telecommunication channels.
Note:
In order for the headset to benefit from this feature, the loudspeaker must provide adequate fidelity delivered
to the ear of the user. Good examples are headsets fitted with a gel ear bud that seals the ear canal,
conversely an open air, hard plastic speaker headset is not a good design for use with the AEQ.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Figure 9.1: Noise- Dependent Volume Control Settings
CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Figure 9.2: Adaptive Equalization Settings Window
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Note:
You can bypass application of the Adaptive EQ in quiet situations by checking the Low Noise Disable LB & HB
option. If this option is selected the adaptive EQ in Mid and High noise situations is still applied.
The AEQ uses the NDVC step (shown as Vol Step: x in the Parameter Manager monitor window) statistic to
determine the switch points from the Low, Mid to High Noise Target Power Ratio curves. CSR recommends that
the step transitions be placed evenly across the range of NDVC steps available (in this case 0 to 5).
Figure 9.3 shows the NDVC at Vol Step: 2, which triggers the Low to Mid Threshold switching from the Low to Mid
Noise Target Power Ratio curve.
Figure 9.3: Adaptive Equalisation Switching to Mid Noise Tier
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
The AEQ applies one of three user shaped curves. These curves are shown as the Low, Mid and High Noise
Target Power Ratio. The user is allowed to shape the curves by setting the low and high band goals in dB. In quiet
conditions the Low Noise Target Power Ratio curve is applied. When the Low to Mid Threshold is crossed, the Med
Noise Target Power Ratio curve is applied. Finally, when the Mid to High Threshold is crossed, the High Noise
Target Power Ratio curve is applied.
Figure 9.4 shows the NDVC at Vol Step: 3, which triggers the Mid to High Threshold switching from the Medium to
the High Noise Target Power Ratio curve.
To tune the AEQ
1.
Initiate a headset call.
2.
To isolate the Adaptive Equalisation, disable any high frequency expansion/enhancement by
checking the Bypass Expanded Bands or Bypass High Frequency Emphasis options (bypassed
throughout the Adaptive Equalisation tuning).
3.
Disable the Adaptive Equalisation by checking the Bypass Adaptive Equalisation option.
4.
The near-end user, while wearing the headset, listens to the original receive speech in a low noise
environment (as confirmed by the AEQ Noise Level statistic).
5.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass Adaptive
Equalisation box and listen to the receive speech (again, for about 30 seconds).
6.
Adjust the spectral shape of the low and high bands by raising/lowering the Low Noise Target Power
Ratio parameters under the appropriate low/high band column(s).
7.
The low and high bands can be disabled for low noise by checking the Low Noise Disable LB & HB
box.
8.
Disable the Adaptive Equalisation by checking the Bypass Adaptive Equalisation option.
9.
The near-end user, while wearing the headset, listens to the original receive speech in a medium
noise environment (as confirmed by the AEQ Noise Level statistic).
10.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass Adaptive
Equalisation box and listen to the equalised receive speech (again, for about 30 seconds).
11.
Adjust the spectral shape of the low and high bands by raising/lowering the Mid Noise Target Power
Ratio parameters under the appropriate low/high band column(s).
12.
Disable the Adaptive Equalisation by checking the Bypass Adaptive Equalisation option.
13.
The near-end user, while wearing the headset, listens to the original receive speech in a high noise
environment (as confirmed by the AEQ Noise Level statistic).
14.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass Adaptive
Equalisation box and listen to the equalised receive speech (again, for about 30 seconds).
15.
Adjust the spectral shape of the low and high bands by raising/lowering the High Noise Target Power
Ratio parameters under the appropriate low/high band column(s).
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Figure 9.4: Adaptive Equalisation Switching to High Noise Tier
AEQ with High Frequency Emphasis or Expansion
9.1.3.1.
Narrow Band plus High Frequency Emphasis
High Frequency Emphasis can be turned on by un-checking the Bypass High Frequency Emphasis option.
High Frequency Emphasis repairs speech information (3469 Hz to 4000 Hz) lost due to low pass filtering
occurring on the PSTN, Cellular Network and Bluetooth connection. Information contained in the original speech
from 281 Hz to 3469 Hz is used to reconstruct the lost high frequency content.
Controls are provided in the column emp. band to adjust the amount of reconstructed high frequency content that
is added to the original speech signal relative to the amount found in the reference speech band (781Hz to
1969Hz).
For example, if emp. band has a value of -16 dB, the reconstructed high frequency signal added to the original
speech signal is 16 dB lower than what is found in the reference speech band.
As with Adaptive Equalisation, the amount of reconstructed high frequency speech can be adjusted depending on
the level of the acoustic background noise. Adjusting the Noise Target Power Ratios defines how much of the
reconstructed speech signal is added based on what the NDVC has set the value of Vol. Step to.
9.1.3.2.
Narrow Band plus Frequency Expansion
When running a system including Frequency Expansion, the AEQ component operates as described in 9.1.2.
Frequency Expansion can be turned on by un-checking the Bypass Expanded Bands option.
Frequency Expansion repairs speech information (3469Hz to 6156Hz) lost due to low pass filtering occurring on
the PSTN, Cellular Network and Bluetooth connection. Information contained in the original speech from 281Hz
to 3469Hz is used to reconstruct the lost high frequency content.
Controls are provided in the expanded bands columns to adjust the amount of reconstructed high frequency
content that is added to the original speech signal relative to the amount found in the reference speech band (781
Hz to 1969 Hz).
For example, if expanded bands has values of -16 dB (for 3469 Hz to 4469Hz) and -26dB (for 4469Hz to
6156Hz), the reconstructed high frequency signal added to the original speech signal is 16dB and 26dB lower
than what is found in the reference speech band, respectively.
As with Adaptive Equalisation the amount of reconstructed high frequency speech can be adjusted depending on
the level of the acoustic background noise. Adjusting the Noise Target Power Ratios defines how much of the
reconstructed speech signal is added based on what the NDVC has set the value of Vol. Step to.
To tune the High Frequency Emphasis Portion of AEQ:
1.
Initiate a headset call.
2.
Disable the High Frequency Emphasis by checking the Bypass High Frequency Emphasis option.
3.
The near-end user, while wearing the headset, listens to the original receive speech in a low noise
environment (as confirmed by the AEQ Noise Level statistic).
4.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass High Frequency
Emphasis option and listen to the receive speech (again, for about 30 seconds).
5.
Adjust the spectral shape of the emphasis band by raising/lowering the Low Noise Target Power
Ratio parameters under the appropriate emp. band column.
6.
The Emphasis Band can be disabled for low noise by checking the Low Noise Disable EBs option.
7.
Disable the High Frequency Emphasis by checking the Bypass High Frequency Emphasis option.
8.
The near-end user, while wearing the headset, listens to the original receive speech in a medium
noise environment (as confirmed by the AEQ Noise Level statistic).
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
9.1.3.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass High Frequency
Emphasis option and listen to the emphasis receive speech (again, for about 30 seconds).
10.
Adjust the spectral shape of the emphasis band by raising/lowering the Mid Noise Target Power Ratio
parameters under the appropriate emp. band column.
11.
Disable the High Frequency Emphasis by checking the Bypass High Frequency Emphasis option.
12.
The near-end user, while wearing the headset, listens to the original receive speech in a high noise
environment (as confirmed by the AEQ Noise Level statistic).
13.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass High Frequency
Emphasis option and listen to the emphasis receive speech (again, for about 30 seconds).
14.
Adjust the spectral shape of the emphasis band by raising/lowering the High Noise Target Power
Ratio parameters under the appropriate emp. band column.
To tune the Frequency Expansion Portion of AEQ:
1.
Initiate a headset call.
2.
Disable the Frequency Expansion by checking the Bypass Expanded Bands option.
3.
The near-end user, while wearing the headset, listens to the original receive speech in a low noise
environment (as confirmed by the AEQ Noise Level statistic).
4.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass Expanded Bands
option and listen to the receive speech (again, for about 30 seconds).
5.
Adjust the spectral shape of the expanded bands by raising/lowering the Low Noise Target Power
Ratio parameters under the appropriate expanded bands column(s).
6.
The expanded bands can be disabled for low noise by checking the Low Noise Disable EBs option.
7.
Disable the Frequency Expansion by checking the Bypass Expanded Bands option.
8.
The near-end user, while wearing the headset, listens to the original receive speech in a medium
noise environment (as confirmed by the AEQ Noise Level statistic).
9.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass Expanded Bands
option and listen to the expanded receive speech (again, for about 30 seconds).
10.
Adjust the spectral shape of the expanded bands by raising/lowering the Mid Noise Target Power
Ratio parameters under the appropriate expanded bands column(s).
11.
Disable the Frequency Expansion by checking the Bypass Expanded Bands option.
12.
The near-end user, while wearing the headset, listens to the original receive speech in a high noise
environment (as confirmed by the AEQ Noise Level statistic).
13.
After listening to about thirty (30) seconds of receive speech, uncheck the Bypass Expanded Bands
option and listen to the expanded receive speech (again, for about 30 seconds).
14.
Adjust the spectral shape of the expanded bands by raising/lowering the High Noise Target Power
Ratio parameters under the appropriate expanded bands column(s).
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
9.
9.1.4.
Side Tone
The CVC HS Side Tone block has a Sidetone Gain setting used to increase or decrease the amount of side tone
heard at the receiver. CVC maintains the same side tone level as the headset user adjusts the volume up or
down setting by the Gain Adjustment Limit. The Sidetone Clip can be set to limit side tone gain that could cause
DAC saturation. A high pass filter can be controlled by the Filter State Off / On radio control, and response set by
the Filter Corner Frequency and Filter Q fields.
To tune the Side Tone:
1.
Initiate a headset call.
2.
Set the mobile phone volume to the maximum.
3.
Set the headset’s volume to the maximum.
4.
Uncheck the Bypass Sidetone and set the Filter State to Off.
5.
The near-end subject speaks a test phrase or a normal conversational phrase, continually.
6.
The near-end subject listens to the side tone signal during single-talk and double-talk conditions at
the far-end.
7.
The near-end subject adjusts the Sidetone Gain parameter to achieve the required amount of side
tone gain.
Note:
Too little side tone may cause the headset to appear to work improperly. Too much side tone can cause
discomfort to the headset user, including a howling/feedback condition.
8.
Would the near-end like to have the side tone increase with changes? If no, skip this field,
otherwise adjust the Gain Adjustment Limit parameter to achieve the required amount of side tone
gain based on volume changes.
9.
Do you want to filter the side tone (for example to reduce road noise)? If no, skip this field,
otherwise set the Filter State to On.
10.
The filter comprises three cascaded bi-quad stages, with each stage user configurable. The GUI
allows the side tone filter EQ parameters to be graphically selected, see Headset Parameter
Manager Users Guide for a more detailed instruction on the EQ.
11.
Figure 9.5, shows a recommended band pass configuration, were low frequency (road noises) and
high frequency (hisses) are rolled-off. The filter helps the side tone from saturating by reducing
unwanted noise while maintaining adequate speech.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Side Tone is the signal picked up by the headset’s microphone and reproduced at the headset’s receiver.
12.
Is the RCV out Peak statistic saturating with near-end speech at maximum volume? If no, skip this
field; otherwise adjust the Sidetone Clip until the saturation is avoided.
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Figure 9.5: Side Tone Generation Settings Window
Document References
Reference
CVC 7th Generation 2-mic Parameter Manager User Guide (BCSW-CVC-HS-5-6-1, B10A)
CS-224237-UG
2-mic Headset Design Guidelines
CS-218321-DC
Terms and Definitions
3GPP
3rd Generation Partnership Project
ADK
Application or Audio Development Kit
AEC
Acoustic Echo Cancellation
AEQ
Adaptive Equaliser
AGC
Automatic Gain Control
AT
Attention (modem command prefix)
B&K
Bruel & Kjaer
BlueCore
Group term for CSR’s range of Bluetooth wireless technology chips.
BlueLab®
CSR’s development toolset for building applications to run in the firmware’s VM.
Bluetooth®
Set of technologies providing audio and data transfer over short-range radio connections.
CDMA
Code Division Multiple Access
CSR
Cambridge Silicon Radio
CVC
Clear Voice Capture DSP audio processing software
CVSD
Continuous Variable Slope Delta Modulation
DAC
Digital to Analogue Converter
DMSS
Dual Microphone Signal Separation
DSP
Digital Signal Processor
DUT
Device Under Test
e.g.
exempli gratia, for example
EQ
Equaliser
GSM
Global System of Mobile Communications
GUI
Graphical User Interface
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
Document
Head and Torso Simulator
HFK
Headset Mode
HS
Headset
HSP
Headset Profile
HTML
HyperText Markup Language
i.e.
Id est, that is
IC
Integrated Circuit
IEC
International Electrotechnical Commission
ITU
International Telecommunication Union
ITU-T
International Telecommunication Union-Telecommunication
MIC
Microphone
MIPS
Million Instructions Per Second
NDVC
Noise-Dependent Volume Control
NS
Noise Suppression
PC
Personal Computer
PLC
Packet Loss Concealment
PS Key
Persistent Store Key
RMS
Root Mean Square
SCO
Synchronous Connection-Oriented Link
SPI
Serial Peripheral Interface
SPKR
Loudspeaker
SPL
Sound Pressure Level
STMR
Side Tone Masking Rating
THD+N
Total Harmonic Distortion + Noise
UFE
Universal Front End
VM
Virtual Machine
© Cambridge Silicon Radio Limited 2012
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CVC 7th Generation Two Microphone ENR Technology for Headsets Tuning Guide
HATS
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