8th Generation 1-mic ENR Technology for Handsfree

8th Generation 1-mic ENR Technology for Handsfree
CVC
®
8th Generation 1-mic ENR Technology for
Handsfree
Tuning Guide
Issue 6
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Document History
Date
History
1
09 DEC 13
Original publication of this document
2
12 DEC 13
Minor editorial changes
3
6 March 14
Edit to the content into the current template
4
22 MAY 14
Editorial updates
5
28 MAY 14
Updated graphics
6
11 JUL 14
Updated for ADK 3.5
Contacts
General information
Information on this product
Customer support for this product
More detail on compliance and standards
Help with this document
www.csr.com
[email protected]
www.csrsupport.com
[email protected]
[email protected]
Trademarks, Patents and Licences
Unless otherwise stated, words and logos marked with ™ or ® are trademarks registered or owned by CSR plc
and/or its affiliates.
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 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Revision
Contents
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Document History ......................................................................................................................................................... 2
Contacts........................................................................................................................................................................ 2
Trademarks, Patents and Licences .............................................................................................................................. 2
Life Support Policy and Use in Safety-critical Compliance............................................................................................ 2
Performance and Conformance .................................................................................................................................... 2
Contents ....................................................................................................................................................................... 3
Tables and Figures ...................................................................................................................................................... 4
1. Introduction ............................................................................................................................................................ 5
1.1. General ........................................................................................................................................................... 5
1.2. Software Versions Supported ......................................................................................................................... 5
1.3. 8th Generation New Features......................................................................................................................... 6
1.4. Before You Begin ........................................................................................................................................... 6
2. Prerequisites .......................................................................................................................................................... 7
2.1. SPI Communication Protocol Drivers ............................................................................................................. 7
2.2. Hardware Interfaces ....................................................................................................................................... 7
2.3. Parameter Manager Tool and User Guide ...................................................................................................... 7
3. Tuning Overview .................................................................................................................................................. 10
3.1. Description of Tuning Stages:....................................................................................................................... 11
3.2. Tuning Flowchart .......................................................................................................................................... 12
4. Tuning Preparation .............................................................................................................................................. 13
4.1. Before You Start Tuning ............................................................................................................................... 13
4.2. Handsfree System In-vehicle ........................................................................................................................ 13
4.3. Phones Models and Network Types ............................................................................................................. 13
4.4. When Using the In-vehicle Audio System ..................................................................................................... 14
4.5. Level Speech Phrase ................................................................................................................................... 15
5. Instrumentation .................................................................................................................................................... 16
5.1. SPL Meter..................................................................................................................................................... 16
5.2. Head and Torso Simulator ............................................................................................................................ 16
6. Tuning Preparation Checklist ............................................................................................................................... 17
7. Quick Start Guide ................................................................................................................................................ 18
7.1. Set Receive Gain Path ................................................................................................................................. 18
7.2. Set Send Gain Path ...................................................................................................................................... 18
7.3. Echo/Doubletalk Performance ...................................................................................................................... 18
8. Tuning Procedures .............................................................................................................................................. 19
8.1. Objective Measurement ................................................................................................................................ 19
8.2. Receive Path Tuning .................................................................................................................................... 19
8.3. Send Path Tuning ......................................................................................................................................... 23
9. Fine-Tuning ......................................................................................................................................................... 32
9.1. Receive Path Fine Tuning ............................................................................................................................ 32
9.2. Send Path Fine Tuning ................................................................................................................................. 34
10.
Advanced Tuning ............................................................................................................................................. 35
10.1.
Advanced Tuning Features ....................................................................................................................... 35
Document References ................................................................................................................................................ 42
Terms and Definitions ................................................................................................................................................. 42
Tables and Figures
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Table 1.1: Part Number Matrix ...................................................................................................................................... 5
Table 5.1: Recommended Meter Settings................................................................................................................... 16
Figure 2.1: CSR ADK Software Setup Window with Driver Installation Option Selected .............................................. 7
Figure 2.2: Accessing Headset Parameter Manager from UFE .................................................................................... 8
Figure 2.3: Parameter Manager Window, Static Mode (Narrow Band Example) .......................................................... 9
Figure 3.1: Processing Blocks on the Parameter Manager Window, Monitoring Mode .............................................. 10
Figure 3.2: The Six CVC HF Tuning Stages ............................................................................................................... 10
Figure 3.3: Tuning Flowchart ...................................................................................................................................... 12
Figure 4.1: A Recorded Waveform of the English Phrase “one two three four five” .................................................... 15
Figure 8.1: Receive Path Processing Blocks .............................................................................................................. 19
Figure 8.2: Packet Loss Concealment Settings Window............................................................................................. 20
Figure 8.3: Receive Automatic Gain Control Settings, Default .................................................................................... 20
Figure 8.4: Adjusting the Speaker Gain ...................................................................................................................... 21
Figure 8.5: Headset Configuration Tool, Audio Gains ................................................................................................. 22
Figure 8.6: Figure Title: Receive Path Noise Suppression Settings Window .............................................................. 23
Figure 8.8: Microphone Gain Settings Window ........................................................................................................... 24
Figure 8.10: Send Path Noise Suppression Settings Window .................................................................................... 26
Figure 8.11: Acoustic Echo Cancellation Settings Window ......................................................................................... 27
Figure 8.12: Non-Linear Processing Settings ............................................................................................................. 29
Figure 8.13: Howling Control Settings......................................................................................................................... 30
Figure 9.1: Hard Clipper Setting Window .................................................................................................................... 33
Figure 9.2: Auxiliary Stream Mix Setting Window ....................................................................................................... 34
Figure 10.1: Noise Dependant Volume Control Settings ............................................................................................ 36
Figure 10.2: Adaptive Equalization Settings Window .................................................................................................. 37
Figure 10.3: Adaptive Equalisation Switching to Mid Noise Tier ................................................................................. 38
Figure 10.4: Adaptive Equalisation Switching to High Noise Tier ............................................................................... 38
1.
Introduction
This document is designed for the Handsfree device manufacturers' audio developers and describes how to tune
Clear Voice Capture (CVC) 1-mic Handsfree (HF) audio processing software running on BlueCore-Multimedia
Integrated Circuit (IC).
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 HF audio
processing block parameters to achieve optimal audio performance.
1.1.
General
The product developer may perform the CVC tuning process at several stages during the Handsfree system’s
development cycle. Typically, a developer fabricates a prototype Handsfree 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 HF application includes default settings that can be used for its audio processing. These defaults may
require gains adjustment 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 the CVC BCSW-CVC-HF-4-7-1 algorithm. 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
(Flash)
BCSW-CVC-HF-4-7-1
A00B
Yes
Yes
BCSW-CVC-HF-4-7-1
CSR8675
(Flash)
BCSW-CVC-HF-4-7-1
A00B
Yes
Yes
BCSW-CVC-HF-4-7-1
Table 1.1: Part Number Matrix
Notes:
CSR8670/CSR8675 support narrow band (NB) using CVSD and includes wide band
(16 kHz sample rate) using modified sub band coding (mSBC).
CSR86xx UFE installer is available at www.csrsupport.com for download.
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
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 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 Handsfree sound quality.
1.3.
8th Generation New Features
CVC’s 1-mic Handsfree solution is in constant development. CSR is adding features and making improvements
driven by the market place.
This section lists improvements made since the previous release (BCSW-CVC-HF-4-6-1, A008) that improve
performance and/or affect the tuning process.
New/improved features include:
CVC Generation 7 feature support

OMS re-factored processing to reduce MIPs

Updated AGC Module that improves tracking of target level

Updated CNG Module that enables selectable coloured noise

PEQ Master Gain independent form bi-quad stages

Tone volumes have been normalised between processing modes with and without CVC
1.4.
Before You Begin
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. Section 3.2
shows a flowchart to help you familiarise yourself with the tuning process.
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide

2.
Prerequisites
This section describes the prerequisites for CVC Handsfree tuning.
2.1.
SPI Communication Protocol Drivers
The CVC HF Parameter Manager tool requires the Serial Peripheral Interface (SPI) drivers. The appropriate drivers
are included in the CSR ADKs, if needed. CSR suggests that you install the ADK from www.csrsupport.com.
Note:
The SPI connection does not work if the SPI device drivers are missing.
Figure 2.1: CSR ADK Software Setup Window with Driver Installation Option Selected
2.2.
Hardware Interfaces
The Parameter Manager and PSTool require a SPI connection to communicate with the target hardware. The
handsfree device 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
Parameter Manager assists the tuning process in the following ways:

Provides 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-HF-4-7-1 Parameter Manager User Guide describes how to use the tool and explains the CVC
parameters, their configuration, valid parameter ranges and their number formats.
The Parameter Manager is accessible through the Universal Front End (UFE) Application.
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
To ensure these drivers are installed during the ADK installation, check the Install the SPI device driver option, see
Figure 2.1.
2.3.1.
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.
CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Figure 2.2: Accessing Headset Parameter Manager from UFE
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Figure 2.3 shows the 1-mic CVC-HF-4-7-1 Handsfree Parameter Manager window that appears when the application
is started i.e. the application is connected and in the Static mode. The application is in a connected mode for a NB
(narrow band, 8000 Hz sample rate) system.
CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Figure 2.3: Parameter Manager Window, Static Mode (Narrow Band Example)
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3.
Tuning Overview
This section describes the overall process for tuning the CVC HF audio processing subsystem and presents the
suggested sequence of the tuning process for CVC handsfree applications.
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 3.2 shows the six stages to the CVC HF tuning process:
TUNING
PREPARATION
OBJECTIVE
MEASUREMENT
(OPTIONAL)
RECEIVE
PATH
TUNING
SEND
PATH
TUNING
FINE
TUNING
ADVANCED
TUNING
(OPTIONAL)
Figure 3.2: The Six CVC HF 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 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Figure 3.1: Processing Blocks on the Parameter Manager Window, Monitoring Mode
3.1.
Description of Tuning Stages:
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 HF algorithm
(PLC, Receive AGC, Speaker Gain, and Noise Suppression).
4.
Send Path Tuning: Focuses on tuning the Send path processing blocks of the CVC HF algorithm
(Microphone Gain, Send AGC, Noise Suppression, Acoustic Echo Canceller and Comfort Noise).
5.
Fine Tuning: The fifth stage at which minor adjustments are made to the processing blocks as required
(Receive AGC, Receive EQ, Clipper, Auxiliary Stream Mix, Send EQ, Send AGC and Send Noise
Suppression)
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 8th Generation CVC.
The following features may be enabled and tuned to enhance the audio performance. However, power consumption
slightly increases as a result.
Enabling and tuning the following processing blocks should be made as required:

Adaptive EQ with Frequency Expansion

NDVC
See sections 4 through section 9 for instructions on successfully completing the six tuning stages.
Notes:
Use the CVC-HF-4-7-1 1-mic Handsfree Parameter Manager User Guide as a reference during the tuning
process.
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.
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
1.
3.2.
Tuning Flowchart
Figure 3.3 shows a suggested procedure to step through the tuning process. Section 7, section 8 and section 9
describe the steps in more detail.
Fine Tuning Process
(See Section 8)
Start cVc HF Tuning
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)
CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Enable PLC
(See Sect. 7.2.2)
Send Path Fine Tuning
Refine EQ, AGC, and Noise
Suppression
(See Sections 8.2.1 – 8.2.3)
Receive AGC
(See Sect. 7.2.3)
SPKR Gain
(See Sect. 7.2.4)
No
Satisfied with Audio
Performance?
Noise Suppression
(See Sect. 7.2.5)
Yes
Send Path Tuning
(See Section 7.3)
MIC Gain
(See Sect. 7.3.1)
Do you want
Advanced Audio
Features enabled?
No
Yes
Send AGC
(See Sect. 7.3.2)
NDVC
(See Sect. 9.1.1)
Noise Suppression and Wind
Noise Reduction
(See Sect. 7.3.3)
Adaptive EQ with Frequency
Expansion
(See Sect. 9.1.3)
Acoustic Echo Canceller
(AEC)
(See Sect. 7.3.4)
Comfort Noise
(See Sect. 7.3.5)
Satisfied with Audio
Performance?
Satisfied with Audio
Performance?
No
No
Yes
Receive Signal Path
Yes
Send Signal Path
End CVC Handsfree
Tuning Complete
Perform if needed
Figure 3.3: Tuning Flowchart
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4.
Tuning Preparation
This version of the CVC software is designed for use with Handsfree devices that have a one microphone input
channel.
Because each CVC software application has a unique acoustical, electrical and mechanical environment in which it
functions, you must 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.
Handsfree System In-vehicle
Before tuning the Handsfree system check the following:
1.
The Handsfree audio components and plastics are production-level or production-intent.
2.
Any microphone wind noise reduction filters are in place.
3.
The device should include SPI connectivity to a PC running the Parameter Manager software tool.
4.
The SPI breakout cabling does not obstruct or interfere with the Handsfree microphone and receiver.
5.
Before testing, the battery is fully charged or has an external power source.
6.
Pair the Handsfree kit to a mobile telephone supporting the Bluetooth Handsfree profiles.
7.
During testing, the Handsfree kit is positioned in its intended location.
8.
Make a short call with the default CVC HF parameters to check the performance before making any
adjustments.
4.3.
Phones Models and Network Types
It is important to understand the general performance of the phones that the Handsfree product will support:

Phone models and local networks vary and affect the sound quality, while also affecting the Handsfree
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 to 16:00 and 19:00 to 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
Handsfree 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 Handsfree 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
Handsfree microphone(s) and speakers.
Note:
Moving the Bluetooth-paired phone to different locations may degrade the Bluetooth link between the phone and
the Handsfree kit. This will affect the sound quality of the Handsfree call.
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
4.2.
For best interoperability between the phone and headset product, CSR recommends the Bluetooth Handsfree Profile
(HFP) with an implementation of AT commands for turning off the mobile phone’s noise reduction and echo
cancellation processing.
4.4.
When Using the In-vehicle Audio System
When using an audio/navigation head-unit, make sure all in-vehicle audio system settings are nominal, such as:

Customisable EQ is flat (Bass, Treble, Mid)

Positioning is set to middle (Fade, Balance)

DSP functions are off (such as concert hall effect, bass extension, and so on)

An eight-speaker premium system

A six-speaker mid-grade system

A non-branded six-speaker base system.
In such cases, CSR recommends first tuning the system that has the highest Sound Pressure Level (SPL) output at
the Handsfree microphone position. When this tuning is complete, check the other audio systems for any problems
in Handsfree sound quality.
Note:
To help minimise sound exposure, CSR recommends using earplugs when testing moderate to high sound
pressure levels.
4.4.1.
Vehicle HVAC Settings
Follow the Heating Ventilation and Air Conditioning (HVAC) fan settings guidelines for each tuning procedure. If the
HVAC setting is not listed, set the HVAC fan speed to either Low or Off. The wind direction should be set towards
the face and foot. Test other conditions when the initial tuning is complete.
4.4.2.
Automotive Factors
Many automotive factors contribute to Handsfree sound quality. When testing, take into consideration the following
conditions and any modifications required made to the tests:

Noise, Vibration, and Harshness effects

Wind Noise

Vehicle Camouflage (pre-production cars)

Engine location (Front/rear-mounted)

Tire Noise

Drive Train (AWD, FWD, RWD)

Body Type (Sedan, Coupe, Convertible, SUV)

Seat Type (Leather, Cloth)

Prototype plastics

Seat Position

Exhaust Noise

Road Condition (Wet, Dry, Bumpy)

Road Surface (Asphalt/Concrete)

Road Traffic

Driving Speed

Electromagnetic Effects, Wiring

Microphone position
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In automotive OEM solutions, it may be required to tune one Handsfree kit packaged with multiple types of audio
systems. For example, a vehicle may offer a Handsfree kit packaged with:

4.5.
Speaker position related to microphone position
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 proves a reasonably stable speech signal
and reduces the dependence on sophisticated test equipment.
Note:
For more precise tuning, a laboratory-based test is required. CSR can carry out laboratory-based tests on
request.
Figure 4.1 shows a recorded waveform of the near-end subject’s voice while speaking the test phrase “one two three
four five” twice.
Figure 4.1: A Recorded Waveform of the English Phrase “one two three four five”
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
When the near-end subject speaks the level speech phrase, measurement of the Sound Pressure Level should be
approximately “90 dB SPL Average (C) Weighted Fast” measured 25 mm from the near end subject’s mouth.
5.
Instrumentation
5.1.
SPL Meter
For measuring Sound Pressure Level (SPL), CSR recommends 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 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 using a Head and Torso Simulator (HATS) capable of electro-acoustic measurements on
telephones per ITU-T recommendations. The HATS system should be capable of testing send/receive frequency
response, send/receive loudness ratings and receive-path THD+N.
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Meter Measurements
6.
Tuning Preparation Checklist
Check
SPI communication to PC


Break-out SPI wiring does not obstruct or interfere with the Handsfree microphone and
receiver


Fully charged Handsfree 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 5.1


Calibrate the Sound Pressure Level Meter to a 1 kHz 94dB re 20μPa sine tone


Ensure all cables and power supplies are in proper working order


Parameter Manager tool connected to the Handsfree system

Accessories

Ear Plugs

Personal

Far-end (landside) subject


Near-end (headset) subject

Documentation

Parameter Manager User Guide
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
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Production or Production-intended Audio Components and Plastics
7.
Quick Start Guide
This section describes how to get started with your CVC algorithm and provide a simple tuning method to set
receive/send gain path and tune for acceptable noise/echo cancellation and doubletalk performance. You may need
to perform additional tuning to achieve optimal performance, depending on the hardware and design of the product.
Before you begin, you must have an active SCO connection, with SPI communication, using the UFE in Monitoring
Mode. To establish this, see Section 2..
7.1.
Set Receive Gain Path
7.2.
Set Send Gain Path
Determine if the echo path signal (loudspeaker at maximum volume) is louder that the speech signal at the
microphone.
If echo is louder than speech:
1.
Adjust the Mic Gain so that the echo signal does not exceed -6 dBfs as seen in the SND IN statistics.
2.
Monitor send speech level as seen in the SND IN statistics. Add Pre-Gain in the SND AGC so this level
enters the SND AGC at approximately -18 dBfs.
If the speech is louder than echo, adjust the microphone gain so speech signal is approximately -18 dBfs as seen in
the SND IN statistics.
See section 7.3.1 for more details on tuning the Mic Gain.
7.3.
Echo/Doubletalk Performance
If less echo is required, increase RER Power and/or decrease RER Adjustment.
If increased doubletalk is required, increase RER Adjustment and/or decrease RER power.
See section 7.3.4 for more details on tuning of the Acoustic Echo Canceller.
Note:
This could take several attempts to find the best ratio of RER Power/RER Adjustment to achieve optimal
doubletalk and echo performance.
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Adjust SPKR Gain to the required maximum volume of the HFK and measure the echo signal at the microphone with
a SPL meter or by measuring the Receive Loudness Rating (RLR). Maximum volume should not exceed 115 dB
peak measured at the microphone to prevent clipping of microphone. See section 7.2.4 for more details.
8.
Tuning Procedures
8.1.
Objective Measurement
After completing the tuning preparation process, the Handsfree device can be acoustically characterised using an
objective telephone sound quality test system. This system normally uses HATS, a PC audio interface, professionalgrade measurement microphones, reference phone system, and measurement software containing standardised test
methods, such as ITU-T and TIA/EIA.
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 .
8.2.
Receive Path Tuning
Figure 8.1 shows the CVC HF Receive Path processing blocks.
Figure 8.1: Receive Path Processing Blocks
Note:
Repeat all tuning measurements at least twice.
8.2.1.
Load Preset Parameters
If the Handsfree device is being tuned for the first time, begin tuning with the default parameters provided with the
CVC HF 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 Handsfree device 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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
8.2.2.
Packet Loss Concealment
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 8.2.
8.2.3.
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, and needs no additional tuning. If additional fine tuning is
required, see section 9.1.2.
Figure 8.3: Receive Automatic Gain Control Settings, Default
Note:
It is possible to bypass the Receive AGC by selecting Bypass Receive AGC. CSR does not recommend
bypassing the Receive AGC.
8.2.4.
SPKR Gain
Tuning the speaker involves determining the maximum receiver volume that the Handsfree device supports. As the
Handsfree 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.
Distortion cannot be eliminated, but efforts must be made to minimise 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.
The amount of distortion in the microphone and speaker determines the maximum volume. In general, limit the
maximum receiver volume to the microphone’s saturation level (approximately “110 dB SPL Average Fast Peek” at
the Handsfree microphone position).
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Figure 8.2: Packet Loss Concealment Settings Window
Before tuning, determine whether the Handsfree system controls the volume of the loudspeaker (via the Bluetooth
volume control) or if an external amplifier (such as an audio/navigation head-unit) controls the volume of the
loudspeaker.
Note:
In kits where the Handsfree system itself controls the volume of the loudspeaker, make sure that the Handsfree
system is at maximum volume when tuning the receive path output level.
In Handsfree kits where an external amplifier (such as an audio head-unit (radio)) controls the volume of the
loudspeaker, the Bluetooth phone should not affect the loudspeaker volume. For these product types, the Speaker
Gain level remains fixed across all phone volumes.
To tune the SPKR Gain:
Initiate a Handsfree 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.
Figure 8.4: Adjusting the Speaker Gain
If there is distortion:
5.
4.1.
The near-end subject lowers the SPKR Gain or enables and adjusts the Clipper:
4.2.
If the clipper is tried, follow the Clipper setup explained in section 9.1.4
4.3.
Optional: The near-end subject adjusts the Boost so that the desired receiver loudness is
maintained.
Headset Configuration Tool, select the Audio Gains tab to configure the required number of volume
steps and set the maximum volume.
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1.
To tune the SPKR Gain with Audio/Navigation Head-Unit Volume Control:
1.
Initiate a Handsfree call.
2.
The far-end subject speaks the level speech phrase.
3.
The near-end subject adjusts loudspeaker volume by clicking on the SPKR Gain block, selecting
Temporarily Override DAC, and adjusting the SPKR Gain to the highest level that does not overload the
audio input to the audio/navigation head-unit and cause distortion.
4.
The far-end subject speaks the level speech phrase.
5.
The near-end subject adjusts the audio/navigation head-unit’s volume level to a level that does not
cause distortion and passes subjective loudness judgment, no larger than “110 dB SPL Average Fast
Peek” at the Handsfree microphone.
Use the Headset Configuration Tool shown in Figure 8.5. Select the Audio Gains tab to configure the SPKR Gain [dB]
values in the VM volume table to be the highest level established in step 3. The SPKR Gain [dB] configuration should
be the same for all HFP Levels. Receive Noise Suppression
The 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 (recommended) and 100%
suppresses up to 20 dB of noise. However the receive signal has been processed by the cellular network and
transmitted over Bluetooth. To avoid over processing the voice, set the aggressiveness conservatively.
To tune for Noise Suppression:
1.
Initiate a Handsfree 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 Aggressiveness for more noise suppression (at the cost of voice quality). Decrease the
Aggressiveness for less noise suppression.
Note:
The far-end subject should avoid using the level speech phrase while tuning the Receive Noise Suppression
Aggressiveness.
Normal conversational speech or phonetically-balanced phrases and passages are better for judging speech
intelligibility in the presence of noise.
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Figure 8.5: Headset Configuration Tool, Audio Gains
High Quality Mode is checked (enabled) by default. This does not affect the noise suppression but provides
improved speech quality.
If voice quality is not critical this option can be un-checked to reduce the processing load. However, because high
quality mode only consumes about 1 MIPS, CSR recommends that it is left enabled.
8.3.
Send Path Tuning
Figure 8.7 shows the CVC software send path processing blocks. The send path processes speech, echo and noise
entering the Handsfree microphone. The echo signal is the result of acoustic coupling from the loudspeaker to the
Send In microphone.
Figure 8.7: Send Path Processing Block Diagram
8.3.1.
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 21.0 dB Pre-amp can be applied to
boost the signal to line level. Figure 8.8 shows a screenshot of the for Mic Gain window.
To tune the MIC Gain (HFK Mode):
1.
Initiate a Handsfree call.
2.
The near-end subject sets the vehicle’s HVAC Fan setting to either Low or Off.
3.
The near-end subject places the Handsfree microphone at the closest specified operating distance
from the near-end subject.
4.
If tuning a Bluetooth Handsfree kit whose volume is controlled by the mobile phone, set the phone’s
volume to maximum. If tuning a Bluetooth Handsfree kit integrated with the car’s stereo system, set the
audio head-unit’s volume to maximum.
5.
The far-end subject speaks the speech level phrase while the near-end subject monitors the MIC GAIN
Peak statistics.
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Figure 8.6: Figure Title: Receive Path Noise Suppression Settings Window
The near-end subject speaks the level speech phrase at approximately “90 dB SPL Average (C)
Weighted Fast” measured 25 mm from the speaker’s mouth and monitors the MIC GAIN Peak
statistics.
7.
Is the MIC GAIN Peak statistics larger during the far-end speech (echo) or the near-end speech? If the
far-end speech (echo) is greater continue. If not, go to step 10.
8.
The far-end subject speaks the speech level phrase while the near-end subject monitors the MIC GAIN
Peak statistics.
9.
The near-end subject adjusts the HFK Mode MIC GAIN so that the MIC GAIN Peak statistics reads no
more than -6 dBFS. End MIC GAIN tuning for far-end speech (echo) is larger than near-end speech.
10.
The near-end subject speaks the speech level phrase while the near-end subject monitors the MIC
GAIN Peak statistics.
11.
The near-end subject adjusts the HFK Mode MIC GAIN so that the MIC GAIN Peak statistics reads no
more than -9 dBFS (-15 to -9 dBFS). End MIC GAIN tuning for near-end speech is larger than far-end
speech (echo).
Figure 8.8: Microphone Gain Settings Window
8.3.2.
Send AGC
The Send AGC automatically adjusts the send path send out signal to a specific level determined by the AGC Target
Level parameter. This parameter compensates for variance in the send out signal levels.
By default, the AGC Target Level is -25 dB 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 Low Echo Coupled Systems (Near-End Send Speech > Speaker Echo):
1.
Initiate a Handsfree call.
2.
The near-end subject places the primary Handsfree microphone at the closest specified operating
distance from the near-end subject.
3.
The near-end subject sets the vehicle’s HVAC Fan setting to either Low or Off.
4.
Next, the near-end subject speaks the level speech phrase at approximately 90 dB SPL Average (C)
Weighted Fast, measured 25 mm from the speaker’s mouth.
5.
The near-end subject adjusts the AGC Target Level to achieve the required listening level at the far-end.
Ensure the speech is not clipping by monitoring the Send Out Peak statistic, avoid saturation. Typically,
the Send AGC should not be raised above -10 dB target scale to allow for overshoot, processing in the
event of saturation or clipping.
6.
The Maximum Gain that can be applied to the signal can also be limited.
7.
The Compression Ratio can also be specified to suit the needs of the application.
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6.
8.
Make sure that the far-end subject never hears clipped or saturated speech.
To tune the AGC Target Level for High Echo Coupled Systems (Loudspeaker Echo > Near-end Send Speech):
Initiate a Handsfree call.
2.
The near-end subject sets the vehicle’s HVAC Fan setting to either Low or Off.
3.
The near-end subject places the Handsfree microphone at the closest specified operating distance
from the loud speaker.
4.
The far-end subject speaks the level speech phrase at approximately “90 dB SPL Average (C)
Weighted Fast” measured 25 mm from the speaker’s mouth.
5.
The near-end subject monitors the Send In Peak MIC statistic.
6.
The near-end subject adjusts the Pre-Gain or Initial Gain so that the Send In Peak MIC statistic added to
the Pre-Gain or Initial Gain yields levels between (-15 to -9 dBFS).
7.
The near-end subject continues to speak the level speech phrase.
8.
The near-end subject adjusts the AGC Target Level to achieve the required listening level at the far-end.
Ensure the speech is not clipping by monitoring the Send Out Peak statistic, avoid Saturation. The
Send AGC Target Level is limited to -3 dB allowing for overshoot.
9.
The Maximum Gain that can be applied to the signal can also be limited.
10.
The Compression Ratio can also be specified to suit the needs of the application.
11.
Make sure that the far-end subject never hears clipped or saturated voices.
Figure 8.9: Send Automatic Gain Control Settings Window
Note:
The Send AGC has two statistics, the Send AGC Applied gain and the Active Speech Level, located directly
below the Send AGC tuning block. They are visible while in monitoring mode to aid in the tuning process.

App 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.

Act Spch: The Active Speech 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.
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1.
8.3.3.
Send Noise Suppression (includes Wind Noise Reduction)
Figure 8.10 shows the Send Path Noise Reduction Setting window. This interface controls both the noise
suppression and wind noise reduction (WNR) parameters.
To tune for 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.
1.
Initiate a Handsfree call.
2.
The near-end subject introduces background noise into the testing environment.
3.
The near-end subject continually repeats a test phrase or a normal conversational phrase,.
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.
High Quality Mode is checked (enabled) by default. This does not affect the noise suppression but provides improved
speech quality. If un-checked, MIPS will be reduced by ~1, but the voice quality will slightly degrade.
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Figure 8.10: Send Path Noise Suppression Settings Window
To tune for Wind Noise Reduction:
The WNR Aggressiveness is the primary tuning parameter. It controls the amount of wind noise reduction that is
applied to the send signal. The WNR Power Threshold controls the trigger point when wind is detected and the WNR
Onset Hold Time parameter determines how long to wait once wind is detected before WNR is applied.
The near-end subject stops, the background noise should be quiet.
2.
To begin tuning WNR, set the WNR Aggressiveness to 100%, set both WNR Power Threshold and WNR
Onset Hold Time to 0.
3.
The near-end subject adds wind using a controlled source (i.e. fan), attempting to maintain a constant
moderate wind speed of approximately 4 mph blowing directly onto the front face of the microphone.
4.
Decrease the WNR Power Threshold until the wind noise is removed. To ensure the threshold is correct,
the near-end subject should switch the WNR on and off by toggling the Bypass Wind Noise Reduction
button, and checking that the wind noise is removed when WRN is on.
5.
Stop the wind, the near-end subject speaks a test phrase or a normal conversational phrase,
continually.
6.
Record or subjectively evaluate the speech quality. If the speech quality (mainly the on-set of speech)
is noticeably degraded, raise the WNR Onset Hold Time until good audio is achieved. To ensure the hold
time is correct, the near-end subject should switch the WNR on and off by toggling the Bypass Wind
Noise Reduction button, and checking the speech quality when the WNR is on.
7.
Now the near-end subject combines both the moderate wind noise and speech phrases.
8.
You can decrease the WNR Aggressiveness until the required level of WNR is achieved, or you can
leave at maximum (100%).
9.
You may need to refine the parameter after the initial tuning.
Note:
Increasing WNR Aggressiveness and decreasing WNR Onset Hold Time achieves more wind noise reduction.
8.3.4.
Acoustic Echo Canceller
This section describes areas to fine-tune on the Acoustic Echo Cancellation Settings window.
Figure 8.11: Acoustic Echo Cancellation Settings Window
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1.
8.3.4.1. Acoustic Echo Cancellation Settings Fields Description

Bypass Residual Echo Reduction: The Bypass Residual Echo Reduction checkbox enables or disables
additional echo cancellation built into the AEC. The intent 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.

Bypass Cross Bin Averaging: This checkbox enables or disables additional calculations built into the
AEC. Bypassing Cross Bin Averaging makes RER attenuation in every frequency bin independent of
each other. Leaving this enabled provides inter-bin dependence, which generally improves double talk
performance.

Reference Delay: This feature compensates for any time delay of the send signal caused by additional

Reference Power Threshold: This is the level in which the receive energy must exceed for the AEC to
adapt. Increasing this value helps keep the AEC from diverging when only noise is present on the
receive path for long periods of time.

RER Adjustment: This is used to control the amount of attenuation when receive speech is present.
Increasing this value will increase double talk performance but can degrade the single talk echo
cancellation performance.

RER Power: This feature controls the number of times the RER attenuation is applied. Increasing this
parameter raises the number of times the RER attenuation is applied.
Tuning the Acoustic Echo Canceller:
1.
Initiate a Handsfree call, set the loudspeaker volume to maximum.
2.
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.
3.
If echo is heard on the far end, increase RER Power by 0.5 and recheck for echo. Increase as needed.
4.
The near end speaks continuous while the far-end speaks short bursts. The far end checks for double
talk attenuation.
5.
First step in tuning for attenuation during double talk is to raise RER Adjustment by steps of 0.5 and
retest. If no increase in performance is achieved, return RER Adjustment to default, which is a value of
10.
6.
If too much attenuation is still applied during double talk, uncheck the Bypass Cross Bin Averaging
check box and retest for double talk attenuation.
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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processing preceding the Acoustic Echo Canceller. This feature ensures that the AEC triggers at the
correct time. The default reference delay value is 2 ms.
8.3.5.
Non-linear Processing
The Non-linear Processing block removes residual echo that the primary AEC is not able to cancel due to a
distortion. It is also used to compensate for the nonlinearities introduced in the receive path. More often, the
reference signal to the AEC is before the volume control of the speaker. Changes in the volume that introduces nonlinear effects in the acoustic path is compensated for by using either the Tier 1 or Tier 2 set of heuristic non-linear
processing. The Tier 1 set can be used with lower speaker volume levels and the Tier 2 set at higher speaker
volume levels. In each of the tiers, the attenuation and the bandwidths, along with the number of bands, can be
selected to improve the compensation for the non-linearities introduced.
There are three tuneable bounds on the Non-linear Processing Settings window:
1.
Lower Bound
2.
Middle Bound
3.
Upper Bound
There is also a Number of Bands and an Attenuation field. The Non-linear Processing algorithm looks between the
Lower Bound and the Middle Bound for the average value and compares it to the internal threshold. Based upon this
average value, the value in the Attenuation field is applied between the Middle Bound and Upper Bound.
Non-linear processing is a two-tier system block. This means that for a receive volume range, two independent nonlinear processors can be used. For example, if the receive volume at the Handsfree microphone has a range of 65
dB SPL to 115 dB SPL, the non-linear processing can be set so that Tier One affects residual echo from 65 SPL to
95 dB SPL, and Tier Two from 95 dB SPL to 115 dB SPL. This is set using the setting Tier-2 Switching Threshold.
Figure 8.12: Non-Linear Processing Settings
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The Tier-2 Switching Threshold of volume level can be selected to transition from Tier 1 to Tier 2 processing.
Typically, non-linear processing needs to be tuned to compensate for poor quality speakers and coarse volume
control mechanisms. For good quality speakers and volume controls, the non-linear processing is turned off to
reduce processing load and improve doubletalk performance.
8.3.6.
Howling Control
When the echo signal surpasses a certain level, the Howling Control can force the CVC Handsfree device to
attenuate the send aggressively (half-duplex).
To fine-tune the Howling Control:
Initiate a Handsfree call.
2.
While the far-end subject checks for echo, the near-end subject increases the Handsfree system
volume until an echo that cannot be cancelled is heard at the far-end.
3.
The far-end subject speaks the level speech phrase while the near-end user monitors the Acoustic
Coupling statistic located below the Acoustic Echo Canceller block on the Parameter Manager window.
4.
To secure an average statistic, repeat this test several times.
5.
Click the Howling Control block to enter the average statistic in the Howling Suppression Coupling
Threshold field.
6.
The far-end subject checks that there is no echo heard at the volume level determined in Step 2. If
echo is present, the near-end reduces the Howling Suppression Coupling Threshold.
Figure 8.13: Howling Control Settings
8.3.7.
Comfort Noise
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.
Figure 8.14: Comfort Noise Settings Window
To tune the Comfort Noise Generator:
1.
Initiate a Handsfree 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.
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1.
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.
9.
Shape can be used to choose the weighting of the comfort noise spectrum.
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9.
Fine-Tuning
When the CVC Handsfree 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 Handsfree sound quality
requirements for the product. This section describes additional tuning instructions for fine-tuning CVC Handsfree
processing modules.
9.1.
Receive Path Fine Tuning
This section describes fine adjustments that can be made to the CVC HF receive path.
Setting Minimum Speaker Gain Loudness
The speaker gain tuning to obtain the maximum loudness setting is described in 8.2.4. 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 Handsfree 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 Headset Configuration Tool. Choose
the Audio Gains tab to configure desired number of volume steps as well as minimum.
9.1.2.
Receive AGC
See section 8.2.3 for information about the Receive AGC tuning.
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 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.
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 target level, while the slope of gain curve
below the target level is unity.
9.1.3.
Receive EQ
The receive path has a parametric equaliser for enhancing audio quality. By default, the parametric equalizer is set
as a high pass filter set to roll off below 125 Hz, 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 BCSW-CVC-HF-4-7-1 1-mic Handsfree Parameter Manager Users Guide for more details.
9.1.4.
Clipper
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. 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).
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9.1.1.
Note:
The Clipper’s Boost setting decreases the dynamic range of the receive signal, which degrades speech quality.
To tune the Clipper:
Initiate a Handsfree call.
2.
Adjust the Handsfree volume to the maximum.
3.
The far-end subject speaks the level speech phrase.
4.
The near-end subject listens for distortion in the Handsfree receiver.
5.
The near-end subject lowers the Clip Point by -3 dB steps, until additional distortion is heard.
6.
Remove the last -3 dB value of added Clip Point and set this as the new Clip Point. End tuning the
clipper.
Optional Steps:
7.
If the Clipper is enabled, the near-end subject can adjust the Boost so that the required receiver
loudness is maintained. Any boost will be hard clipped at the Clip Point.
8.
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 9.1: Hard Clipper Setting Window
9.1.5.
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
receive out signal. Changing a stream mix using a slider will inversely control the other to maintain 100% between
the channels.
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.
The auxiliary signal can be boosted by using the Auxiliary Gain parameter. The maximum limit on the auxiliary gain is
24 dB.
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1.
9.2.
Send Path Fine Tuning
This section describes fine adjustments to the CVC Handsfree send path.
9.2.1.
Send EQ
The send path has a parametric equaliser for enhancing audio quality. Normally, the parametric equalization 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 the
BCSW-CVC-HF-4-7-1 1-mic Handsfree Parameter Manager User Guide for more details.
Gain should be minimised (unity) through the EQ to avoid saturation and distortion.
9.2.2.
Send AGC
To fine-tune the Send AGC:
1.
Adjust the AGC Target Level to the required value. The default is -25 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.
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 target level, while the slope of gain curve
below the target level is unity.
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Figure 9.2: Auxiliary Stream Mix Setting Window
10.
Advanced Tuning
10.1. Advanced Tuning Features
For Handsfree products that offer adequate fidelity you can enable advanced CVC features that include the
Noise-Dependent Volume Control (NVDC) and AEQ.
10.1.1. Noise-Dependent Volume Control
The NDVC should be tuned after the MIC Gain. See section 8.3.1 for instructions on tuning the MIC Gain.
A properly tuned NDVC will result when the DAC proportionally increases with the near end noise level, creating a
constant SNR environment for the near end listener.
To tune the NDVC:
1.
Initiate a Handsfree 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 60 mph). Monitor the Noise Level statistic and
place this value in the Max noise level field.
6.
During the high “road” 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.
Note:

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. Under the
highest noise condition, the maximum loudness is limited to SPKR Gain at 0 dB or the highest level
defined in the Volume table.

The Total SPKR Gain = SPKR Gain + Maximum NDVC Gain Limit

The Total SPKR Gain is important when tuning the Send Path.

The NDVC gain change is quantised based on the DAC resolution of roughly 3 dB per step. For
example, setting the Maximum NDVC Gain Limit to 15 dB equals 5 steps on the DAC.
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 0.75.
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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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.
Note:
Figure 10.1 shows the default settings, however the Max noise level and Min noise level need to be adjusted for
your specific Handsfree device.
10.1.2. Adaptive EQ (AEQ)
There are three systems available for the CSR86xx:

Narrow Band plus High Frequency Emphasis: An AEQ (0 to ~3.5 kHz) plus the addition of an Emphasis
Band (~3.5 to 4 kHz).

Narrow Band plus Frequency Expansion: An AEQ (0 to ~3.5 kHz) plus the addition of Expanded Bands
(~3.5 to ~6.2 kHz).

Wide Band: An AEQ (0 to 8 kHz).
When Adaptive Equalization 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.
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.
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 Equalization also has the capability to compensate for variations in voice transmission channels, which
include far-end devices and telecommunication channels.
Note:
For the Handsfree device to benefit from this feature, the loudspeaker must provide adequate fidelity delivered
to the ear of the user and the NDVC has been enabled and tuned.
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Figure 10.1: Noise Dependant Volume Control Settings
CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
Figure 10.2: Adaptive Equalization Settings Window
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 and finally when the Mid to High Threshold is crossed the High Noise Target
Power Ratio curve is applied.
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Note:
There is the option to 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 10.3 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 10.4 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.
Figure 10.4: Adaptive Equalization Switching to High Noise Tier
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Figure 10.3: Adaptive Equalisation Switching to Mid Noise Tier
To tune the AEQ:
Initiate a Handsfree 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 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 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 approximately 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 use 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 approximately 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).
10.1.3. AEQ with High Frequency Emphasis or Expansion
10.1.3.1. 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 (781 Hz to 1969 Hz).
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 Equalzation, 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.
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1.
10.1.3.2. 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 (3469 Hz to 6156 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 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).
As with Adaptive Equalization 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 Handsfree call.
2.
Disable the High Frequency Emphasis by checking the Bypass High Frequency Emphasis option.
3.
The near-end user 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 listens to the original receive speech in a medium noise environment (as confirmed
by the AEQ noise level statistic).
9.
After listening to approximately thirty (30) seconds of receive speech, uncheck the Bypass High
Frequency Emphasis option and listen to the emphasis receive speech (again, for approximately 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 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 approximately 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.
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For example, if expanded bands has values of -16 dB (for 3469 Hz to 4469 Hz) and -26 dB (for 4469 Hz to 6156
Hz), the reconstructed high frequency signal added to the original speech signal is 16 dB and 26 dB lower than what
is found in the reference speech band, respectively.
To tune the Frequency Expansion Portion of AEQ:
Initiate a Handsfree call.
2.
Disable the Frequency Expansion by checking the Bypass Expanded Bands option.
3.
The near-end user 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 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 approximately 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 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 approximately 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 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
1.
Document References
Document
Reference
1-mic Handsfree Parameter Manager User Guide (BCSW-CVC-HF-4-7-1)
CS-309820-UG
Terms and Definitions
3rd Generation Partnership Project
ADC
Analogue to Digital Converter
ADK
Audio or Application Development Kit
AEC
Acoustic Echo Cancellation
AEQ
Adaptive Equalizer
AGC
Automatic Gain Control
AT
Attention (modem command prefix)
B&K
Bruel & Kjaer
BCSW
BlueCore Software
BlueCore
Group term for CSR’s range of Bluetooth wireless technology chips.
Bluetooth®
Set of technologies providing audio and data transfer over short-range radio connections.
CDMA
Code Division Multiple Access
CODEC
Coder Decoder
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
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CVC 8th Generation 1-mic ENR Technology for Handsfree Tuning Guide
3GPP
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