Electro-Acoustic Recommended Minimum Performance

Electro-Acoustic Recommended Minimum Performance
3GPP2 C.S0056-0
Version 1.0
Date: July 22, 2005
Electro-Acoustic Recommended Minimum Performance
Specification for cdma2000 Mobile Stations
COPYRIGHT
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Requests for reproduction of this document should be directed to the 3GPP2
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Organizational Partner’s documents should be directed to that Organizational Partner.
See www.3gpp2.org for more information.
Revision History
Revision
C.S0056-0 v1.0
Description
Initial Publication
Date
July 22, 2005
3GPP2 C.S0056-0 v1.0
CONTENTS
NORMATIVE REFERENCES................................................................................................ vii
INFORMATIVE REFERENCES............................................................................................ viii
1
2
Introduction ................................................................................................................ 1-1
1.1
Scope .................................................................................................................... 1-1
1.2
Terms.................................................................................................................... 1-1
Electro-Acoustic Requirements ................................................................................... 2-1
2.1
Receive Audio Interface ......................................................................................... 2-1
2.1.1
2.1.1.1
Definition.................................................................................................. 2-1
2.1.1.2
Method of Measurement ........................................................................... 2-1
2.1.1.3
Minimum Standard .................................................................................. 2-1
2.1.2
2.2
Definition.................................................................................................. 2-2
2.1.2.2
Method of Measurement ........................................................................... 2-2
2.1.2.3
Minimum Standard .................................................................................. 2-2
Send Audio Interface............................................................................................. 2-2
Send Audio Frequency Response .................................................................... 2-2
2.2.1.1
Definition.................................................................................................. 2-2
2.2.1.2
Method of Measurement ........................................................................... 2-3
2.2.1.3
Minimum Standard .................................................................................. 2-3
2.2.2
Send Audio Sensitivity .................................................................................... 2-4
2.2.2.1
Definition.................................................................................................. 2-4
2.2.2.2
Method of Measurement ........................................................................... 2-4
2.2.2.3
Minimum Standard .................................................................................. 2-4
2.2.3
3
Receive Audio Sensitivity ................................................................................ 2-2
2.1.2.1
2.2.1
2.3
Receive Audio Frequency Response ................................................................ 2-1
Weighted Terminal Coupling Loss................................................................... 2-4
2.2.3.1
Definition.................................................................................................. 2-4
2.2.3.2
Method of Measurement ........................................................................... 2-4
2.2.3.3
Minimum Standard .................................................................................. 2-5
Loudness Contrast ................................................................................................ 2-5
2.3.1
Definition ........................................................................................................ 2-5
2.3.2
Method of Measurement ................................................................................. 2-5
2.3.3
Minimum Standard ........................................................................................ 2-5
Electro-acoustic Standard Test Conditions ................................................................. 3-1
3.1
Reference Base Station Simulator Requirements .................................................. 3-1
3.1.1
Receive Level................................................................................................... 3-1
3.1.2
Send Level ...................................................................................................... 3-1
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3.1.3
Other Requirements........................................................................................ 3-1
3.2
Ear Simulators...................................................................................................... 3-1
3.3
Acoustic Test Signals ............................................................................................ 3-2
3.3.1
Normal Test Signal ......................................................................................... 3-2
3.3.2
Echo-Loss Test Signal..................................................................................... 3-2
3.4
Standard Test Conditions ..................................................................................... 3-2
ANNEX A:
Loudness Rating Conversions ....................................................................... A-1
ANNEX B:
Maximum Acoustic Pressure Level ................................................................ B-1
ANNEX C:
Ear Simulator................................................................................................ C-1
C.1
Artificial Ears........................................................................................................ C-1
C.2
Type 1................................................................................................................... C-1
C.3
Type 2................................................................................................................... C-2
C.4
Type 3................................................................................................................... C-2
C.4.1
Type 3.2.......................................................................................................... C-2
C.4.2
Type 3.3.......................................................................................................... C-3
C.4.3
Type 3.4.......................................................................................................... C-3
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TABLES
Table 2.1-1. Receive Frequency Response Mask ............................................................... 2-1
Table 2.2-1. Send Frequency Response Mask ................................................................... 2-3
Table 3.2-1. Acceptable Ear Simulators ............................................................................ 3-1
Table C.1-1. Ear Simulator Types ..................................................................................... C-1
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FIGURES
Figure 2.1-1 Receive Frequency Response Mask ............................................................... 2-2
Figure 2.2-1 Send Frequency Response Mask................................................................... 2-4
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Notes
1. “Base station” refers to the functions performed on the land side, which are typically
distributed among a cell, a sector of a cell, and a mobile communications switching
center.
2. This standard uses the following verbal forms: “Shall” and “shall not” identify
requirements to be followed strictly to conform to the standard and from which no
deviation is permitted. “Should” and “should not” indicate that one of several
possibilities is recommended as particularly suitable, without mentioning or excluding
others; that a certain course of action is preferred but not necessarily required; or that
(in the negative form) a certain possibility or course of action is discouraged but not
prohibited. “May” and “need not” indicate a course of action permissible within the
limits of the standard. “Can” and “cannot” are used for statements of possibility and
capability, whether material, physical, or causal.
3. The following operators define mathematical operations:
x indicates multiplication.
/ indicates division.
+ indicates addition.
- indicates subtraction.
* indicates complex conjugation.
∈ indicates a member of the set.
x indicates the largest integer less than or equal to x: 1.1 = 1, 1.0 = 1.
|x| indicates the absolute value of x: |-17|=17, |17|=17.
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NORMATIVE REFERENCES
The following standards contain provisions which, through reference in this text,
constitute provisions of this Standard. At the time of publication, the editions indicated
were valid. All standards are subject to revision, and parties to agreements based on
this Standard are encouraged to investigate the possibility of applying the most recent
editions of the standards indicated below. ANSI and TIA maintain registers of currently
valid national standards published by them.
1.
ANSI S1.4-1983 (R2001), American National Standard Specification for Sound
Level Meters.
2.
ANSI S1.4A-1983 (R2001), Amendment 1 - American National Standard
Specification for Sound Level Meters.
3.
IEEE Std 269-2002, Standard Method for Measuring Transmission Performance of
Analog and Digital Telephone Set, Handsets and Headset.
4.
ITU-T Recommendation G.122, Influence of National Systems on Stability and
Talker Echo in International Connections, 1993.
5.
TIA/EIA-690, Recommended Minimum Standards for 800 MHz Subscriber Units,
November 2000.
6.
3GPP2 C.S0014-0, Enhanced Variable Rate Codec (EVRC), December 1999.
7.
3GPP2 C.S0011-C, Recommended Minimum Performance Standards cdma2000
Spread Spectrum Mobile Stations, 2005.
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INFORMATIVE REFERENCES
At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this Standard are encouraged to
investigate the possibility of applying the most recent editions of the standards
indicated below. ANSI and TIA maintain registers of currently valid national standards
published by them.
8.
IEEE Std 661-1979, IEEE Standard Method for Determining Objective Loudness
Ratings of Telephone Connections.
9.
ITU Recommendation P.79, Calculation of loudness ratings for telephone sets,
September 1999.
10.
TIA/EIA-810-A, Telecommunications - Telephone Terminal EquipmentTransmission Requirements for Narrowband, December 2000.
11.
TIA/EIA-579-A, Telecommunications Telephone Terminal Equipment Transmission
Requirements for Digital Wireline Telephones, November 1998.
12.
IEC 60950-1, Information Technology Equipment – Safety –Part 1: General
Requirements, October 2002
13.
ITU Recommendation P.501, Test signals for use in telephonometry, May 2000.
14.
TIA-470.110-C, Telecommunications — Handset Acoustic Performance
Requirements for Analog Terminal Equipment Connected to the Public Switched
Telephone Network.
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1.1
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1.2
INTRODUCTION
Scope
This document details definitions, methods of measurement, and minimum electroacoustic performance characteristics for Code Division Multiple Access (CDMA) mobile
stations. These standards are intended to ensure a level of electro-acoustic performance
approaching that defined by the ITU-T for PSTN circuits. These electro-acoustic
requirements are applicable to all Speech Service Options supported by the mobile
station. These requirements are applicable to mobile station handsets. Requirements for
loudspeaker, headset, and hands-free configurations are not addressed in the current
document and are for further study. Test methods are recommended in this document;
however, methods other than those recommended may suffice for the same purpose.
Terms
Base Station. A station in the Domestic Public Cellular Radio Telecommunications
Service, other than a mobile station, used for radio communications with mobile
stations.
Codec. The combination of an analog-to-digital encoder and a digital-to-analog decoder
in series (encoder/decoder).
dBA. A-weighted sound pressure level expressed in decibels obtained by the use of a
metering characteristic and the weighting A specified in [1] and [2].
dBm. A measure of power expressed in terms of its ratio (in dB) to one milliwatt.
dBm0. Power level expressed in dBm relative to an arbitrarily defined reference point
called the zero transmission level point, or 0 TLP [3].
dBPa. A measure of sound pressure level expressed in terms of its ratio (in dB) to one
Pascal, 20 log10 (Pressure/1 Pa). 1 Pa = 1Newton/m2.
dBSPL. A measure of Sound Pressure Level expressed in terms of its ratio in (dB) to 20
µPa, 20 log10 (Pressure/20µPa). dBPa is preferred.
Drum Reference Point (DRP). Point located at the end of the ear canal, corresponding
to the ear-drum position.
Decoder. A device for the translation of a signal from a digital representation into an
analog format, for the purposes of this standard, a cdma2000®1 compatible device.
Ear Reference Point (ERP). See section 3.20 of [3].
Encoder. A device for the coding of a signal into a digital representation, for the
purposes of this standard, a cdma2000 compatible device.
Mobile Station. A station in the Domestic Public Cellular Radio Telecommunications
Service. It is assumed that mobile stations include portable units (for example, handheld personal units) and units installed in vehicles.
Mouth Reference Point (MRP). See section 3.30 of [3].
Nominal Volume Control Setting. Reference Receive Volume Control Setting, see
section 3.38 of [3].
1 cdma2000® is the trademark for the technical nomenclature for certain specifications and
standards of the Organizational Partners (OPs) of 3GPP2. Geographically (and as of the date of
publication), cdma2000® is a registered trademark of the Telecommunications Industry Association
(TIA-USA) in the United States.
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RLR. Receive Loudness Rating, a measure of receive audio sensitivity.
SLR. Send Loudness Rating, a measure of transmit audio sensitivity.
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2.1
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2.1.1
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2.1.1.1 Definition
ELECTRO-ACOUSTIC REQUIREMENTS
Receive Audio Interface
Receive Audio Frequency Response
The audio frequency response of the mobile station earpiece is defined as the variation
of the ratio of the acoustic output of the earpiece to the signal input at a reference base
station as a function of frequency. For this measurement, the manufacturer shall
specify whether the measurement is referred to ERP or to DRP.
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2.1.1.2 Method of Measurement
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2.1.1.3 Minimum Standard
The receive audio frequency response shall be measured according to [3], using a
speech-like test signal as described in 3.3.1.
The receive audio frequency response shall lie within the floating mask defined by the
mandatory upper and the mandatory lower boundary limits specified in Table 2.1-1.
The receive audio frequency response should lie within the floating mask defined by the
desired upper and the desired lower boundary limits specified in Table 2.1-1. The
points in the table shall be interpolated linearly on a log frequency scale to form
piecewise linear upper and lower bounds. The manufacturer shall specify whether the
measurement is referred to ERP or to DRP. The receive frequency response mask shall
apply at the nominal volume control setting, see 2.1.2.3.
Table 2.1-1. Receive Frequency Response Mask
Frequency
(Hz)
Mandatory Upper
Limit
(dB)
200
0
300
400
0
800
+9
Mandatory Lower
Limit
(dB)
Desired Upper
Limit
(dB)
0
-34
-14
-9
-8
1000
0
1600
+6
3000
3400
Desired Lower
Limit
(dB)
-9
+9
-8
+6
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Figure 2.1-1 Receive Frequency Response Mask
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2.1.2
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2.1.2.1 Definition
Receive Audio Sensitivity
The receive audio sensitivity is the ratio of the acoustic output of the mobile station
earpiece to the electrical input at a reference base station expressed as a Receive
Loudness Rating (RLR). The reference point shall be ERP for this measurement.
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2.1.2.2 Method of Measurement
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2.1.2.3 Minimum Standard
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2.2.1
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2.2.1.1 Definition
The measurements shall be performed at both nominal and maximum volume settings.
RLR is measured according to the procedure given in [3] using a speech-like test signal
as described in 3.3.1.
RLR shall be between -5 dB and +5 dB, and the nominal target value should be 0 dB2 .
Where a user controlled receive volume control is provided, the nominal volume control
setting is the setting that results in an RLR value closest to the nominal RLR. In cases
where consecutive volume control settings result in RLR values that are equally far from
the nominal RLR, the louder setting shall be selected. With the receive volume control
set to maximum, the RLR shall not be less than (louder than) -18 dB.
Send Audio Interface
Send Audio Frequency Response
The audio frequency response of the mobile station transmitter is defined as the
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In a future revision of this document, the nominal value may be changed to +2 dB to be
consistent with other electro-acoustic specifications.
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variation of the ratio of the output from a reference base station to the acoustic input at
the mobile station microphone as a function of frequency.
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2.2.1.2 Method of Measurement
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The send audio frequency response shall be measured according to [3], using a speechlike test signal as described in 3.3.1 and using the mouth simulator as specified in [3].
2.2.1.3 Minimum Standard
The send audio frequency response shall lie within the floating mask defined by the
mandatory upper and the mandatory lower boundary limits specified in Table 2.2-1.
The send audio frequency response should lie within the floating mask defined by the
desired upper and the desired lower boundary limits specified in Table 2.2-1. The
points in the table shall be interpolated linearly on a log frequency scale to form
piecewise linear upper and lower bounds.
Table 2.2-1. Send Frequency Response Mask
Frequency
Mandatory Upper
Limit
Mandatory Lower
Limit
Desired Upper
Limit
Desired Lower
Limit
(Hz)
(dB)
(dB)
(dB)
(dB)
200
+3
300
+3
-12
-5
500
-3
1000
+3
-3
+3
2000
+10
-3
+8
3000
3400
-11
+10
-3
+8
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Figure 2.2-1 Send Frequency Response Mask
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2.2.2.1 Definition
Send Audio Sensitivity
The send audio sensitivity is the ratio of the acoustic sound pressure input at the
mobile station microphone to the resulting output of a reference base station expressed
as a Send Loudness Rating (SLR).
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2.2.2.2 Method of Measurement
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2.2.2.3 Minimum Standard
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2.2.3.1 Definition
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2.2.3.2 Method of Measurement
SLR is measured according to the procedure given in [3] using a speech-like test signal
as described in 3.3.1 and using the mouth simulator as specified in [3].
The SLR shall fall within the range +19 to +6 dB, and the nominal target value should
be +11 dB3.
Weighted Terminal Coupling Loss
The weighted terminal coupling loss (TCL W) is the ratio of the rms spectrum of the
electrical input signal to the rms spectrum of the output signal of a reference base
station simulator in conjunction with the mobile station under test. The echo signal
results from acoustic coupling between the mobile station earpiece and the mobile
station microphone.
The echo frequency response in a mobile handset is measured in accordance with [3]
using a speech-like test signal as described in 3.3.2. An alternative signal may be used
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In a future revision of this document, the nominal value may be changed to +8 dB to be
consistent with other electro-acoustic specifications.
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provided that its crest factor is low enough to allow sufficient dynamic range for the
measurement.
The weighted terminal coupling loss is calculated from the echo
frequency response according to [4] Annex B, Clause B.4.
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2.2.3.3 Minimum Standard
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2.3
With the receive volume control set to maximum, the weighted terminal coupling loss
shall be at least 45 dB during single talk conditions.
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2.3.3
Loudness Contrast
Definition
Loudness contrast is defined for both send and receive paths. Send loudness contrast
is the difference between analog send loudness and digital send loudness. Receive
loudness contrast is the difference between analog receive loudness and digital receive
loudness. This test applies only to mobile stations that support operation in both
analog mode and digital mode.
Method of Measurement
The measurements shall be performed at both nominal and maximum volume settings.
Analog measurements will be performed applying a –50 dBm RF signal and a 6000 Hz
SAT at ±2.0 kHz peak frequency deviation [5].
Measure and record receive sensitivity per section 2.1.2 for digital and analog operation.
Measure and record send sensitivity per section 2.2.2 for digital and analog operation.
Minimum Standard
The contrast in send and receive loudness ratings between analog and digital modes for
a given mobile station shall not exceed 3 dB.
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3.1
ELECTRO-ACOUSTIC STANDARD TEST CONDITIONS
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3.1.2
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3.2
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Reference Base Station Simulator Requirements
Receive Level
A Digital Test Sequence (DTS) representing the reference base station simulator’s codec
equivalent of an analog sinusoidal signal whose rms value is 3.17 dB below the fullscale sinusoid capacity of the codec shall generate a level of 0dBm0 at the PSTN
network [6], [3].
In analog operation, the reference base station simulator shall set the audio level so
that a received 1004 Hz tone with a ±2.9 kHz peak frequency deviation produces a level
of –18dBm0 at the PSTN network.
All signal levels will have a tolerance of ±0.5 dB as specified in [3].
All levels are specified in a 600 Ohm system [3].
Send Level
A sinusoidal signal with a level of 0dBm0 shall produce the digital test sequence (DTS)
representing the codec equivalent of an analog sinusoidal signal whose rms value is
3.17 dB below the full-scale sinusoidal capacity of the codec [6], [3].
In analog operation, the reference base station simulator shall set the send level so that
a 1004 Hz tone with a level of -18 dBm0 at the PSTN network produces a ±2.9 kHz
peak frequency deviation of the transmitted carrier.
All signal levels will have a tolerance of ±0.5 dB as specified in [3].
All levels are specified in a 600 Ohm system [3].
Other Requirements
Other requirements for the reference base station simulator are defined in 6.4.3 of [7].
In analog operation the reference base station simulator shall support the compandor,
pre-emphasis, and de-emphasis defined in [5] as necessary to perform the
measurements defined in 2.3.
Ear Simulators
One of the ear simulators listed in Table 3.2-1 shall be used.
Table 3.2-1. Acceptable Ear Simulators
Ear Simulator
Type 3.2 Simplified pinna simulator, low leak
Notes
[3]
Type 3.2 Simplified pinna simulator, high leak
[3]
Type 3.3 Anatomically shaped soft pinna
[3]
Type 3.4 Simplified soft pinna
[3]
If using the Type 3.2 Simplified Pinna Simulators, care must be taken to ensure that
there is no additional leakage other than that provided by the simulator. Care must also
be taken to ensure that the cavity size of the simulator is unchanged when sealed to the
handset. A customized mold may be used to achieve this seal. An adapter made out of
flexible sealing material may be used provided that the above criteria are met.
Meticulous care should be taken, with any method, to ensure consistent repeatable
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results.
The manufacturer shall specify the ear simulator to be used for testing. The specified
ear simulator shall be used for all tests.
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3.3.1
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3.3.2
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3.4
Acoustic Test Signals
The test stimuli for the level, gain, frequency-response, and echo-loss measurements in
this document are based on natural speech. The use of natural-speech based stimuli is
predicated by the inherent nature of CDMA vocoders, which were designed for speech
signals. Modified-IRS speech was used, since that weighting has been the default for
recent CDMA-vocoder Selection and Characterization tests. In addition, this weighting
provides for a spectrally “flatter” signal.
Normal Test Signal
The default test stimulus for the level, gain, and frequency-response measurements is
Normal.pcm (alternatively Normal.wav).
This Modified-IRS weighted, multi-talker
speech signal consists of four male and four female talkers, each presenting a different
sentence-pair from a Harvard phonetically-balanced list. The presentation of the
talkers is alternated by gender. The resulting activity factor of the composite signal is
77.4%. The level for each talker is coarsely normalized, and the overall active level of
the composite signal is finely adjusted to a level of –19 dBm0 (the default nominal
speech level used in recent CDMA-vocoder Selection and Characterization tests). A
1004 Hz calibration tone at this level is also provided to assist in setup of the
measurement facility. This stimulus has been shown to provide for very good level,
gain, and frequency-response measurement capability, in an appropriately configured
measurement facility.
Echo-Loss Test Signal
The default test stimulus for the echo-loss measurement is EchoLoss.pcm (alternatively
EchoLoss.wav). The basis for this specific stimulus is the Normal.pcm signal described
above, level adjusted to an active level of –20 dBm0 (the native nominal level for the
following process system). The –20 dBm0 Normal.pcm signal was peak-compressed
using a 16-bit 2’s-complement digitally-implemented parametric amplifier, which
provided for a programmed level of instantaneous gain above a set digital threshold,
and a unity gain below the threshold value. Compression was used to limit the
peak/active-rms factor of the stimulus, allowing for further resolution in the echo-loss
measurement. The compressor threshold was set at a digital level of |3620|, and the
compression factor was set at 4.2 dB/dB. This processing provided for an initial
nominal pk/active-rms ratio of 10 dB, which, following filtering to the analysis
bandwidth, resulted in a usable pk/active-rms of nominally 12.5 dB. The active-level of
the resulting modified composite signal is finely adjusted to a level of -10 dBm0. This
stimulus has been shown to provide for echo-loss measurement capability in excess of
50 dB, in an appropriately configured measurement facility.
Standard Test Conditions
All tests shall be performed with a call set up using RC3 and service option 3 unless
otherwise specified. See 6.5.2 of [7] for comments that apply to all tests unless
otherwise specified.
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ANNEX A: Loudness Rating Conversions
This annex is informative.
The loudness ratings defined in [8] may be approximated from those defined in [9], as
described by [10], as follows:
SLR ([11]) = TOLR ([8]) + 57
RLR ([11]) = ROLR ([8]) - 51
Results obtained with the above conversions should be used for reference only. These
conversions are based upon approximated frequency response curves as specified in
[10]. Proper conversions may depend on actual measurements being made with each
measurement standard where frequency responses deviate significantly from the norm.
This section has been referenced from Annex T3 of [3].
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ANNEX B: Maximum Acoustic Pressure Level
This annex is informative.
Maximum acoustic pressure requirements are defined in [12]. A test signal appropriate
for use with the codecs employed by cdma2000 mobile stations is needed.
The recommended test stimulus for the short-duration measurement is PeakLevel.pcm
(alternatively PeakLevel.wav). It is based on the 12burshp.pcm artificial signal that was
provided as a potential candidate for general use as a stimulus in the measurements
specified in this document. This 12-tone signal consists of the 65 lines of the P.501 [13]
signal, broken into 12 vocals played in a random sequence. Each vocal consists of 5 or
6 lines that are harmonics of the fundamental. The vocals were additionally spectrally
shaped to be more quasi-speech-like in nature.
While this signal proved less than satisfactory for use as a general stimulus in this
MPS, a clipped version of this signal can be used as a stimulus for the specific peak
acoustic level test. The signal is level adjusted in a hard limiting digitally-implemented
amplifier such that the peak level of the composite signal is at the digital limits of the
amplifier. The signal is then given a 25 dB gain. The resulting 25 dB clipped composite
signal has 72.5% of its samples at the digital limits of the output of the amplifier.
When this stimulus is appropriately interfaced to the system, a measurable portion of
the acoustic output of the mobile terminal will potentially be at the peak output level.
An appropriately interfaced peak-sampling sound-pressure level meter can then be
used to measure such peak acoustic transitions.
An appropriate test signal for the long-duration measurement is for further study.
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ANNEX C:
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C.1
Ear Simulator
Artificial Ears
Measurements on telephone handsets have been traditionally done using the ITU-T
P.57 Type 1 ear simulator. This ear simulator includes the IEC 318 coupler, which was
introduced to the market nearly three decades ago. The Type 1 ear simulator is a
rather coarse simulation of the human ear, and the conditions under which it is
designed to be used are not achievable for many modern small or unusually shaped
handsets. Therefore, some new ear simulators have been specified by ITU (International
Telecommunication Union) which better simulate the acoustical load of the human ear
when using modern telephone handsets. The various types of ear simulators are
provided in Table C.1-1.
Table C.1-1. Ear Simulator Types
ITU-T P.57
Ear Type Earphone Types
Measuring point
1
Supra-aural, supra-concha
close to ERP
2
Insert earphones
DRP
3.1
Intra-concha earphones
DRP
3.2
Supra-aural, supra-concha
DRP
3.3
Supra-concha
DRP
3.4
Supra-concha
DRP
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Type 1
The coupler in the Type 1 ear simulator is further specified in IEC Publication 318. It is
recommended that the Type 1 ear simulator be used for measurements on supra aural
and supra-concha earphones, sealed, intended for normal telephone bandwidth (100Hz
to 4 kHz) applications. The acoustic input impedance and frequency sensitivity
response of the Type 1 artificial ear are referred directly to the Ear Reference Point
(ERP) using an individual calibration curve. The Type 1 ear simulates the acoustic load
of the human ear under no leakage conditions, and is therefore only applicable when
the telephone handset is held completely sealed to the ear. This is not a very realistic
situation for normal use of handsets. Therefore, a correction curve LE is used for
Loudness Rating calculations according to ITU-T P.79 to simulate a leak condition.
However, this correction factor has been derived for old telephone handsets where the
leak was rather small. The leak obtained with modern handsets is often very different
from the nominal LE correction curve. In addition, it is extremely difficult to seal the
handset to the coupler and the use of a custom “form” or some pliable putty is required
for smaller handsets common in cellular telephony. Repeatability, when using pliable
putty to seal the handset to the artificial ear, can be very good if only small amounts of
putty are required, but may be poor if the handset does not fit well to the artificial ear
and large amounts of putty are required.
ADVANTAGES: Simple; long history of use.
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DISADVANTAGES: Does not model typical leakage encountered in real life use of
modern telephones; less accurate representation of real ear; repeatability problems may
exist where sealing to the handset is difficult; inappropriate for modern low impedance
or wideband handsets;
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C.4.1
Type 2
The Type 2, also referred to as the IEC711 ear simulator, is used for measurements on
insert earphones, both sealed and unsealed, such as hearing aids and headsets. The
sound pressure measured by the Type 2 ear simulator is referred to the ear-drum
reference point (DRP). Therefore a correction function (ITU-T P.57) is used for converting
data to the ear reference point (ERP) when it is required to calculate loudness ratings or
check results against specifications based on measurements referred to ERP. Type 2
couplers are only appropriate for testing insert type headsets.
Type 3
Type 3.24
All Type 3 artificial ears consist of the Type 2 IEC 711 occluded-ear simulator, to which
an ear canal extension terminated with a pinna simulation device is added. The Type
3.2 ear simulator uses a simplified pinna simulator. In this simulator, a well-defined
leak (available in two grades) from the cavity to the exterior simulates the average real
ear loss for telephone handsets which are held either comfortably (low-leak version) or
loosely (high-leak version) against the human ear. Type 3.2 ear simulator is
recommended for measurements on supra-aural and supra-concha earphones, sealed
and unsealed, and of both high and low impedance (practically covering all kinds of
earphone acoustic designs provided it fits the mechanical design). It can be used in the
wide frequency range from 100 Hz to 8 kHz. The Type 3.2 ear simulator was made with
the anatomically shaped Type 3.3 ear simulator as a reference. The acoustical behavior
of the Type 3.2 high leak ear simulator is therefore very close to that of the Type 3.3.
Measurements with Type 3.2 ear simulator are done at the eardrum position (DRP). By
using the individually calibrated frequency response supplied with the ear simulator,
the measurements can be referred to ERP, when it is required to calculate loudness
ratings or check results against specifications based on measurements referred to ERP.
It should be noted that the normal calibration of this device is performed with reference
to ERP at 1 kHz. The Type 3.2 coupler is a much more accurate representation of the
human ear than the Type 1 coupler, in terms of impedance, and provides a realistic and
repeatable leak. It shares with the Type 1 coupler the phone to coupler sealing
problem, that is, the handset must still be sealed to the coupler (so that the defined
leak is the only leak) and this necessitates the use of putty or other sealing material.
This again may affect measurement repeatability if the handset does not fit well to the
artificial ear and large amounts of putty are required. An alternative is to provide an
adaptor for the phone which attaches directly to the coupler and provides a mirror
image of the telephone earpiece, sealing completely and repeatably.
ADVANTAGES: Realistic representation of ear acoustical impedance, and “real world”
leak
DISADVANTAGE: Repeatability problems may exist where sealing to the handset is
difficult
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An earlier wide band coupler, using the Type 1 IEC coupler and an adaptor, the so called
“German Leak Ring” has been used for some years. Not standardized, it is seldom used today.
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C.4.3
Type 3.3
The Type 3.3 ear simulator is a very close simulation of a real human ear realized by
terminating the ear canal extension with an anatomically shaped pinna simulator as
described in IEC959. The pinna simulator is made of a high-quality elastomer with a
well specified shore-A hardness.
It is recommended that the Type 3.3 ear simulator is used for measurements on supra
concha earphones, sealed and unsealed and especially those which, due to their
peculiar shape, do not fit the circular rims of Type 1 or Type 3.2 ear simulators,
whichever is applicable. The sound pressure measured by the Type 3.3 ear simulator is
referred to DRP. Therefore a correction curve (same as for Type 2) is used to convert
data to the ERP when it is required to calculate loudness ratings or check results
against specifications based on measurements referred to the ERP. The Type 3.3 ear
has several advantages. First it is, arguably, the most accurate representation of real
use of a telephone. It also allows the same fixture to be used for handsfree telephony
and headset testing. There is no need for any sealing material to be used, as the leak
provided is “natural”. Even with mechanical positioning systems to aid the user, it does
require meticulous care in fixing the telephone in place to provide repeatable results.
Some testing has shown that this can be difficult, leading to variation in measurements
from test to test and from lab to lab. In addition, the pinna is somewhat fragile, and
requires care in handling in order to maintain its integrity. Several versions of pinna
hardness have historically been available causing possible confusion. The
recommended guidelines for placing a handset against the Type 3.3 ear may not match
with how a real user would position the handset against his ear.
ADVANTAGES: Most flexible and realistic representation of use
DISADVANTAGES: Repeatability may be poor.
Type 3.4
The pinna simulation is realized in Type 3.4 ear simulator by terminating the drum
reference plane of the Type 2 ear simulator with an ear canal extension and a simplified
pinna made of an elastomer with a well defined shore-A hardness. It is suggested that
Type 3.4 can be used as a simplified alternative to Type 3.3 for measurements on
supra-concha and supra-aural handsets, where the pressure dependent
characterization of receiving performance is considered important. It is not
recommended for headsets. The sound pressure measured by the Type 3.4 ear
simulator is also referred to DRP and therefore the DRP-ERP correction curve (the same
as for Type 2 and Type 3.3) must be used when comparing data with measurements
obtained. The Type 3.4 pinna provides somewhat better repeatability than the Type 3.3
pinna, but is less accurate in its simulation of the acoustic impedance and volume of
the human ear.
ADVANTAGES: Repeatability is easier than Type 3.3.
DISADVANTAGES: Less accurate representation of real ear acoustic impedance.
Cannot be used for headsets.
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