Download 15 hearing aid compatibility - Telecommunications Industry

Telecommunications Industry Association
TR41.9-08-05-012-L
Document Cover Sheet
Project Number
PN-3-3602-AD1 (to become Addendum 1 to TSB-31-C)
Document Title
Proposed Changes for Section 15 on Hearing Aid Compatibility
Source
VTech Communications
Contact
Stephen R Whitesell
2 Shannon Ct
Howell, NJ 07731
Distribution
TR-41.9
Intended Purpose
of Document
(Select one)
X
Phone: 732 751 1079
Fax:
Email: [email protected]
For Incorporation Into TIA Publication
For Information
Other (describe) -
The document to which this cover statement is attached is submitted to a Formulating Group or
sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the
provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of
which provisions are hereby incorporated by reference.
Abstract
Contribution TR-41.9-07-05-014 by Glenn Hess of MWM Acoustics pointed out that the hearing aid
compatibility (HAC) magnetic field test procedures in Clause 15.1 of then draft TSB-31-C required
acoustic tests to determine the input signal level to be used for certain types of digital telephones but
failed to described the artificial ear to be used. It also suggested a broadband signal be used instead a
1000 Hz tone for this purpose. Further discussion during the May 2007 TR-41.9 meeting suggested some
additional changes might be needed in both Clauses 15.1 and 15.2.
Contribution TR-41.9-07-11-010-L provided the initial draft of specific changes to these two clauses.
The addition of information on the artificial ear was added to Clause 15.1, but the use of a broadband test
signal was not addressed. Several additional changes were proposed from the viewpoint of organization,
clarity, and correctness. A number of questions were included in that draft and discussed during the
November 2007 meeting, with comments captured in an MR1 revision during the meeting. There was a
continued interest expressed in incorporating broadband test signals for the measurements, but no specific
text has been forthcoming.
This draft incorporates the results of the November 2007 discussions. Some changes have been made in
the Suggested Equipment List (SEL) items identified for each test, including the addition of SEL#70 for a
level recorder previously shown in the figures but not otherwise identified. The use of the high leak
condition instead of the low leak condition has been specified for the Type 3.3 artificial in keeping with
changes being made to other standards by TR-41.3. Broadband test signals are not included, but the
author recommends going ahead to ballot with the addendum document as it now stands.
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5.5 Selected Equipment List (SEL)
. . . . .
(70) Level recorder: device used in conjunction with a sinewave frequency generator
(SEL#27 or SEL#54) and frequency selective voltmeter (SEL#28) or true rms ac
voltmeter (SEL#40) to produce a graphical representation of the variation of signal
level (in dB) vs. frequency displayed on a logarithmic axis.
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15 HEARING AID COMPATIBILITY
15.1 Hearing Aid Compatibility – Magnetic Field Intensity 47 CFR, 68.316
15.1.1 Background
The United States Congress enacted legislation requiring that persons using hearing
aids with magnetic pickups have reasonable access to the National Telephone Network.
Telephones imported and manufactured after August 16, 1989 have to be hearing aid
compatible (HAC) as defined in 47 CFR, 68.316. Cordless telephones were initially
exempted but also have to be HAC if imported or manufactured after August 16, 1991.
Secure telephones approved by the U.S. Government for transmission of classified or
sensitive voice communications are exempt. HAC requirements for mobile phones, as
found in 47 CFR Part 20, are not covered by the testing procedures described below.
15.1.2 Purpose
To determine the magnetic field characteristics of hearing aid compatible handsets to
ensure adequate magnetic coupling of voice signals.
15.1.3 Equipment
(1)
Sinewave frequency generator SEL#54.
(2)
Frequency selective voltmeter SEL#28.
(3)
Hearing aid probe assembly SEL#29.
(4)
Level recorder SEL#70
(5)
Artificial ear SEL#51 for testing telephones with handsets that seal on this type of
artificial ear.
(6)
Artificial ear SEL#69 for testing telephones with handsets that do not seal on artificial
ear SEL#51.
(7)
Standard microphone SEL#52.
(8)
Microphone amplifier SEL#53.
(9)
Zero level encoder/decoder for all digital interface types under test (e.g. T1, ISDN)
SEL #32
Note: Refer to subclause 5.5 for equipment details.
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15.1.4 Equipment States Subject To Test
Normal off-hook talking condition.
15.1.5 Test procedure
15.1.5.1 Axial Field Intensity and Frequency Response (Reference Figure 1, EIA504 as contained in 47 CFR, 68.316).
(1) Connect the telephone under test as shown in Figure 15.1-1 for analog telephones,
Figure 15.1-2 for ISDN telephones, Figure 15.1-3 for proprietary and special use
telephones, or Figure 15.1-4 for IP-based telephones.
(2) Set the input at 1000 Hz across the 10 ohm resistor of the matching pad to -10 dBV
for analog telephones or -3 dBV for ISDN telephones.
(3) For proprietary, special use and IP-based telephones, an appropriate input test level
that produces an equivalent acoustic level to analog sets (nominally 0 dBPa) with
the receive volume control set to its nominal gain level needs to first be determined.
(a) Connect the telephone under test as shown in Figure 15.2-3 for proprietary
and special use telephones or Figure 15.2-4 for IP-based telephones. The
test arrangements are the same as in Figures 15.1-3 and 15.1-4 except that
the acoustic output of the handset is measured instead of the magnetic
output. The reference codecs and the analog telephone / IP terminal adapter
shown in these figures need to be capable of encoding or decoding analog
signals with zero loss.
(b) Place the handset receiver on artificial ear SEL#69 using the high leak
condition specified in ANSI/TIA-470.110-C-1 for analog telephones and in
ANSI/TIA-810-B for digital telephones. Alternatively, the handset receiver
may be placed on artificial ear SEL#51 if a seal can be achieved between the
handset surface and the rim of the artificial ear without the use of sealing
putty or similar materials.
(c) Use the laboratory standard pressure microphone for measuring the sound
pressure generated in the artificial ear. Feed the output of the microphone
through the microphone amplifier to the frequency selective voltmeter.
(d) Apply a 1000 Hz input signal from the sinewave generator and measure the
microphone output signal using the frequency selective voltmeter. Determine
the sound pressure produced in the artificial ear taking into account the
microphone sensitivity (in dBV/Pa), the gain (if any) of the microphone
amplifier, and the reading of the frequency selective voltmeter (in dBV).
Adjust the input level to produce 0 dBPa at 1000 Hz. Use the input level thus
determined for the magnetic field measurement.
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(4) Measure the axial component of the magnetic field 10 mm in front of the reference
plane defined by the handset earcap and along a measurement axis parallel to and
displaced no more than 10 mm from the reference axis running through the center of
the earcap hole pattern. Position the telephone handset receiver and probe coil for a
maximum axial reading subject to the above constraints and measure the output of the
probe coil with the frequency selective voltmeter. Determine the magnetic field
intensity taking into account the probe coil sensitivity (in dBV/(A/m)) and the reading of
the frequency selective voltmeter (in dBV).
(5) Using the same axial probe coil location and input signal level as in (4), vary the
frequency of the sinewave signal generator from 300 to 3300 Hz. Measure the probe
coil voltage output with the frequency selective voltmeter and record the probe coil
voltage frequency response using the level recorder. When testing IP-based
telephones (e.g. VoIP telephones), ensure the duration of the test signals are longer
than the packet delay (generally ranging from 100 ms to 300 ms) so the frequency
selective voltmeter can capture the maximum axial field intensity readings at each of
the measurement frequencies.
(6) Compare the recorded frequency response with the appropriate template (Figure 4A or
4B, EIA 504 as contained in 47 CFR 68.316) based on the level of the axial 1000 Hz
field intensity determined in (4).
15.1.5.2
Radial Field Intensity (Reference Figure 1, EIA-504 as contained in 47
CFR, 68.316).
(1)
Connect the telephone under test as shown in Figure 15.1-1 for analog telephones,
Figure 15.1-2 for ISDN telephones, Figure 15.1-3 for proprietary and special use
telephones, or Figure 15.1-4 for IP-based telephones.
(2)
Set the input at 1000 Hz across the 10 ohm resistor of the matching pad to -10 dBV
for analog telephones or -3 dBV for ISDN telephones.
(3)
For proprietary, special use and IP-based telephones, an appropriate input test level
that produces an equivalent acoustic level to analog sets (nominally 0 dBPa) with the
receive volume control set to its nominal gain level needs to first be determined.
(a) Connect the telephone under test as shown in Figure 15.2-3 for proprietary
and special use telephones or Figure 15.2-4 for IP-based telephones. The
test arrangements are the same as in Figures 15.1-3 and 15.1-4 except that
the acoustic output of the handset is measured instead of the magnetic
output. The reference codecs and the analog telephone / IP terminal adapter
shown in these figures need to be capable of encoding or decoding analog
signals with zero loss.
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(b) Place the handset receiver on artificial ear SEL#69 using the high leak
condition specified in ANSI/TIA-470.110-C-1 for analog telephones and in
ANSI/TIA-810-B for digital telephones. Alternatively, the handset receiver
may be placed on artificial ear SEL#51 if a seal can be achieved between the
handset surface and the rim of the artificial ear without the use of sealing
putty or similar materials.
(c) Use the laboratory standard pressure microphone for measuring the sound
pressure generated in the artificial ear. Feed the output of the microphone
through the microphone amplifier to the frequency selective voltmeter.
(d) Apply a 1000 Hz input signal from the sinewave generator and measure the
microphone output signal using the frequency selective voltmeter. Determine
the sound pressure produced in the artificial ear taking into account the
microphone sensitivity (in dBV/Pa), the gain (if any) of the microphone
amplifier, and the reading of the frequency selective voltmeter (in dBV).
Adjust the input level to produce 0 dBPa at 1000 Hz. Use the input level thus
determined for the magnetic field measurement.
(4)
Measure the radial component of the magnetic field at four points 90 degrees apart
in a plane 10 mm above and parallel to the reference plane defined by the handset
earcap, and at a distance greater than or equal to 16 mm from the measurement
axis used for the axial component measurement in 15.1.5.1 (4). Position the
telephone handset receiver and probe coil for a maximum radial reading at one of
the radial measurement points subject to the above constraints and measure the
output of the probe coil with the frequency selective voltmeter. Determine the
magnetic field intensity taking into account the probe coil sensitivity (in dBV/(A/m))
and the reading of the frequency selective voltmeter (in dBV). Repeat the
measurement for the three additional radial measurement points.
15.1.6 Alternative Methods
None suggested.
15.1.7 Suggested Test Data
(1)
Input applied to the telephone in dBV.
(2)
For proprietary, special use, and IP-based telephones, identify the type of artificial
ear used for determining the input level.
(3)
Axial field intensity and frequency response
(a) Output of probe coil at 1000 Hz in dBV.
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(b) 1000 Hz sensitivity of probe coil in dBV/(A/m).
(c) Calculated 1000 Hz field intensity in dB relative to 1 Ampere/meter.
(d) Frequency.
(e) Output of probe coil in dBV for each frequency other than 1000 Hz.
(f) Normalized frequency response (Net change in dBV output of probe coil
relative to 1000 Hz output for each frequency.)
(g) Plot of normalized frequency response relative to appropriate template
limits.
(4)
Radial field intensity
(a) Measurement angle.
(b) Output of probe coil at 1000 Hz in dBV.
(c) 1000 Hz sensitivity of probe coil in dBV/(A/m).
(d) Calculated 1000 Hz field intensity in dB relative to 1 Ampere/meter.
15.1.8 Comments
(1)
The probe coil output may be amplified, if needed.
(2)
For telephone sets that provide the ability to adjust the receive level, the volume
control may be adjusted to any available setting when checking for compliance with
the magnetic coupling hearing aid compatibility requirement. For proprietary, special
use and IP-based telephones, the volume control may be readjusted after the input
level necessary to produce 0 dBPa acoustic output has first been established with
the volume control gain set to its nominal level.
(3)
A Helmholtz coil, built in accordance with IEEE standard 1027 is required to calibrate
the hearing aid probe. The calibration procedure in clause 5 of IEEE Standard 1027
is recommended.
(4)
The integrator described in subclause 4.3 and Annex A of IEEE Standard 1027 are
not used when making the frequency response measurements. The frequency
response templates (Figure 4A and 4B, EIA 504 as contained in 47 CFR 68.316)
include the 6 dB per octave characteristic of the hearing aid probe coil. Any deviation
from the 6 dB per octave slope noted during the calibration procedure using the
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Helmholtz coil is to be included in the measurements. The hearing aid voltage at
1000Hz is to be used as the 0 dB level in the templates. In other words, the
frequency response curve passes through the 0 dB, 1000 Hz point of the figures.
(5)
The requirements in 47 CFR, 68.316 only address characteristics applicable to the
desired voice signal. Informal FCC complaints about digital cordless telephones in
the 2004 time-frame led to the development of standard TIA-1083, which also
provides requirements related to undesired noise signals.
Feeding Circuit
890 ohm
1 F
Analog Telephone
Under Test
2H
400 ohm
Telephone Handset
Receiver
-10 dBV
Sinewave
Generator
10 ohm
1250 ohm
2W
ProbeCoil
48 V
Level
Recorder
Frequency Selective
Voltmeter
Figure 15.1-1 Setup for testing 47 CFR, 68.316 HAC for Analog Telephone
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890 ohm
-3 dBV
Sinewave
Generator
10 ohm
ISDN Telephone
Under Test
ISDN
Telephone
Reference
Codec
ISDN
Telephone
Interface
Telephone Handset
Receiver
ProbeCoil
Level
Recorder
Frequency Selective
Voltmeter
Figure 15.1-2 Setup for testing 47 CFR, 68.316 HAC for ISDN Telephone
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Circuit “A”
Feeding Circuit
2 F
Circuit “B”
Loop Simulator
Circuit “C”
DC Blocking Circuit
2 F
2H
400 ohm
2 F
TR41.9-08-05-012-L
48 V
2 F
2H
400 ohm
2 F
2 F
Proprietary
Telephone
Reference Codec
Proprietary Telephone
Under Test
Host System
Circuit
“C”
T1 Zero Loss
Codec
Telephone Handset
Receiver
T1 Interface
Sinewave
Generator
ProbeCoil
Proprietary
Telephone
Interface
Circuit
“A”
Loop Start
Interface
Circuit
“B”
Analog Telephone
Interface
Level
Recorder
Frequency Selective
Voltmeter
Figure 15.1-3 Setup for testing 47 CFR, 68.316 HAC for Proprietary and Special
Use Telephone
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Circuit “A”
Feeding Circuit
Circuit “B”
Loop Simulator
2 F
2 F
2H
400 ohm
48 V
2 F
Circuit
“C”
Sinewave
Generator
Circuit “C”
DC Blocking Circuit
2 F
2H
400 ohm
2 F
TR41.9-08-05-012-L
2 F
T1 Zero Loss
Codec
T1 / IP
Gateway
Circuit
“A”
Loop Start / IP
Gateway
Circuit
“B”
Analog Telephone
IP Terminal
Adapter
IP-Based Telephone
Under Test
10/100/1000
Base-T
Ethernet
Hub
Telephone Handset
Receiver
ProbeCoil
Level
Recorder
Frequency Selective
Voltmeter
Figure 15.1-4 Setup for testing 47 CFR, 68.316 HAC for IP-based Telephone
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15.2 Hearing Aid Compatibility - Volume Control 47 CFR, 68.317
15.2.1 Background
The HAC Act required the FCC to establish regulations that would ensure reasonable
access to telephone service by persons with hearing disabilities. The FCC requires
hearing aid compatible telephones to provide volume control.
15.2.2 Purpose
To determine that the receive volume control of a telephone with a handset or headset
meets specified requirements for loudness at its normal unamplified level and provides
the required amount of gain at its maximum volume setting. Loudness is measured in
terms of Receive Objective Loudness Rating (ROLR), and gain is measured in terms of
change in ROLR.
15.2.3 Equipment
(1)
Sinewave frequency generator SEL#54.
(2)
Frequency selective voltmeter SEL#28.
(3)
Level recorder SEL#70.
(4)
Artificial ear SEL#51 for testing telephones with handsets that seal on this type of
artificial ear.
(5)
Artificial ear SEL#69 for testing telephones with handsets that do not seal on artificial
ear SEL#51.
(6)
Standard microphone SEL#52.
(7)
Microphone amplifier SEL#53.
(8)
Test loops or commercially available artificial loop equivalent to 2.7 km and 4.6 km
#26 AWG non-loaded cable SEL#50.
(9)
Zero level encoder/decoder for all digital interface types under test (e.g. T1, ISDN)
SEL #32
Note: Refer to subclause 5.5 for equipment details.
15.2.4 Equipment States Subject To Test
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Normal off-hook talking condition.
15.2.5 Test procedure
(1)
Connect the telephone under test as shown in Figure 15.2-1 for analog telephones,
Figure 15.2-2 for ISDN telephones, Figure 15.2-3 for proprietary and special use
telephones, or Figure 15.2-4 for IP-based telephones. The reference codecs and the
analog telephone / IP terminal adapter shown in these figures need to be capable of
encoding or decoding analog signals with zero loss.
(2)
Place the handset receiver on artificial ear SEL#69 using the high leak condition
specified in ANSI/TIA-470.110-C-1 for analog telephones and in ANSI/TIA-810-B for
digital telephones. Alternatively, the handset receiver may be placed on artificial ear
SEL#51 if a seal can be achieved between the handset surface and the rim of the
artificial ear without the use of sealing putty or similar materials.
(3)
Use the laboratory standard pressure microphone for measuring the sound pressure
generated in the artificial ear. Feed the output of the microphone through the
microphone amplifier to the frequency selective voltmeter.
(4)
The ROLR of the telephone under test is to be determined first with the receive
volume control at its normal unamplified level. If the manufacturer does not define a
normal unamplified level, either by some marking on the phone (e.g., label at a slide
switch detent position) or by some explanation in the user manual, the minimum
volume control setting is to be used as the normal unamplified level.
(5)
Set the sinewave generator to 1000 Hz and adjust its output to produce -10 dBV
across the 10 ohm resistor of the matching pad for analog telephones or -3 dBV for
ISDN telephones. For proprietary, special use and IP-based telephones, adjust the
sinewave generator to produce an equivalent acoustic level to analog sets (nominally
0 dBPa) with the receive volume control set to its nominal gain level.
(6)
With the output level of the sinewave generator held constant, logarithmically sweep
the frequency range from 200 to 4000 Hz at a rate of one complete sweep in
approximately 8 to 10 seconds. When testing the IP-based telephones (e.g. VoIP
telephones), the effects of packet delay (generally ranging from 100 ms to 300 ms) in
the 10/100/1000 Base-T Ethernet hub or the IP network need to be taken into
account. The test signal from the sinewave frequency generator should be
synchronized correctly with the frequency selective voltmeter and level recorder to
capture the maximum readings at each of the measuring frequencies.
(7)
Determine the sound pressure produced in the artificial ear taking into account the
microphone sensitivity (in dBV/Pa), the gain (if any) of the microphone amplifier, and
the reading of the frequency selective voltmeter (in dBV). Record the sound
pressure on the level recorder.
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(8)
Determine the ROLR of the telephone under test by calculating the ROLR from the
measured frequency response as specified in IEEE 661-1979 (R1998).
Measurements of ROLR for analog telephones are to be made for loop conditions
represented by 0, 2.7 and 4.6 km of 26 AWG non-loaded cables or equivalent. No
variation in loop conditions is required for ISDN, proprietary and special use, and IPbased telephones since the receive level of ISDN, proprietary and special use, and
IP-based telephones are independent of loop length.
(9)
Verify that the ROLR falls between the upper and lower limits defined in subclause
4.1.2 of ANSI/TIA-470-A for analog telephones or defined in subclause 4.3.2.2 of
ANSI/TIA-579 for ISDN, proprietary and special use, and IP-based telephones. If the
manufacturer has not defined a normal unamplified level and if the telephone does
not meet the ANSI/TIA-470-A / ANSI/TIA-579 requirements at its minimum volume
control setting, the setting should be increased and steps (5) through (8) repeated to
find the minimum volume control setting that does meet the requirements. This
setting is then taken as defining the normal unamplified level.
(10)
Adjust the volume control of the telephone under test to its maximum volume
setting and repeat steps (5) through (8).
(11)
Subtract the ROLR value determined for the maximum volume control setting in
step (10) from that determined for the nominal volume control setting in step (8) or
step (9) to determine compliance with the gain requirement. Verify that the minimum
gain requirement is achieved without significant clipping of the test signal.
(12)
If the gain exceeds 18 dB, force the telephone to pass through a proper on-hook
transition and repeat steps (5) through (8) to determine if the gain automatically
resets to the normal unamplified level.
(13)
If significant clipping is detected at the maximum gain setting, and if the gain is
greater than the minimum required value, the volume control of the telephone under
test should be adjusted to a lower setting and steps (5) through (8) and (11) repeated
to determine if the minimum required gain relative to the normal unamplified level
can be achieved without significant clipping of the test signal.
15.2.6 Alternative Methods
Although 47 CFR, 68.317 specifies the receive volume control requirement in terms of
ROLR as defined in IEEE 661-1979 (R1998), current industry standards TIA-470.110-C
(replaces TIA-470-A) and TIA-810-B (replaces TIA-579) have shifted to measuring receive
loudness in terms of Receive Loudness Rating (RLR) as defined by ITU-T
Recommendation P.79. Annex G of TIA-470.110-C provides the following relationship
between these two loudness rating measures:
ROLR (IEEE 661) = RLR (ITU-T P.79) + 51 dB
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This relationship may be used to determine if RLR values obtained according to the
methods in TIA-470.110-C and TIA-810-B comply with Part 68 criteria specified in terms
of ROLR.
15.2.7 Suggested Test Data
(1)
State the type of artificial ear used for the tests.
(2)
If the test results were determined as ITU-T P.79 RLR values, show those values
and the conversion to ROLR values.
(3)
State the ROLR level measured with the gain setting at the normal unamplified level.
For analog telephones state the ROLR levels separately for each of the 0, 2.7 and
4.6 km test conditions. Indicate whether the ROLR level complies with the upper and
lower ROLR limits required by of ANSI/TIA-470 for analog telephones or by
ANSI/TIA-579 for ISDN, proprietary and special use, and IP-based telephones. If the
manufacturer did not indicate the gain setting for the normal unamplified level, state
whether the minimum gain setting or some other gain setting was used for
determining compliance with this requirement.
(4)
State the ROLR level measured at the maximum receive volume control setting and
the amount of gain relative to the normal unamplified level. For analog telephones,
state the ROLR levels and gains separately for each of the 0, 2.7, and 4.6 km test
conditions. Indicate if the EUT provides the required minimum gain.
(5)
If the gain at the maximum receive volume control setting exceeds 18 dB, state if the
amplified receive capability automatically resets to the nominal unamplified level
when the telephone is forced to pass through a proper on-hook transition.
(6)
State whether significant clipping was detected at the maximum gain setting. If so,
state if there was a lower volume control setting that provided the minimum required
gain without producing significant clipping.
15.2.8 Comments
(1)
This requirement applies to telephones with receive volume control.
(2)
ROLR is a loudness rating value expressed in dB of loss. More positive values of
ROLR represent lower receive levels.
(3)
47 CFR, 68.317 indicates the minimum gain requirement is to be met without
significant clipping of the test signal, but it does not specify what constitutes
significant clipping. Compliance with this requirement may be determined by a
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subjective listening test. If an objective measurement is used, greater than 10% total
harmonic distortion might be considered significant clipping.
(4)
The FCC has established a streamlined waiver process to allow telephones primarily
intended for use by hard of hearing people to have an override switch that allows the
gain to exceed 18 dB without automatically resetting to the normal unamplified level
if certain warning information is provided. See FCC Memorandum Opinion and
Order DA 01-578.
Feeding Circuit
890 ohm
Artificial Line
(0, 2.7, or 4.6 km
26 AWG non-loaded)
1 F
2H
400 ohm
Telephone Handset
Receiver
-10 dBV
Sinewave
Generator
10 ohm
Analog Telephone
Under Test
400 ohm
2W
Artificial Ear
& Microphone
48 V
Microphone
Amplifier
Level
Recorder
Frequency Selective
Voltmeter
Figure 15.2-1 Setup for testing 47 CFR, 68.317 HAC volume control for Analog
Telephone
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890 ohm
-3 dBV
Sinewave
Generator
10 ohm
ISDN Telephone
Under Test
ISDN
Telephone
Reference
Codec
ISDN
Telephone
Interface
Telephone Handset
Receiver
Artificial Ear
& Microphone
Microphone
Amplifier
Level
Recorder
Frequency Selective
Voltmeter
Figure 15.2-2 Setup for testing 47 CFR, 68.317 HAC volume control for ISDN
Telephone
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Circuit “A”
Feeding Circuit
2 F
Circuit “B”
Loop Simulator
Circuit “C”
DC Blocking Circuit
2 F
2H
400 ohm
2 F
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48 V
2 F
2H
400 ohm
2 F
2 F
Proprietary
Telephone
Reference Codec
Proprietary Telephone
Under Test
Host System
Circuit
“C”
T1 Zero Loss
Codec
Telephone Handset
Receiver
T1 Interface
Sinewave
Generator
Artificial Ear
& Microphone
Proprietary
Telephone
Interface
Circuit
“A”
Loop Start
Interface
Circuit
“B”
Analog Telephone
Interface
Level
Recorder
Microphone
Amplifier
Frequency Selective
Voltmeter
Figure 15.2-3 Setup for testing 47 CFR, 68.317 HAC volume control for
Proprietary and Special Use Telephone
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Circuit “A”
Feeding Circuit
Circuit “B”
Loop Simulator
2 F
2 F
2H
400 ohm
48 V
2 F
Circuit
“C”
Sinewave
Generator
Circuit “C”
DC Blocking Circuit
2 F
2H
400 ohm
2 F
TR41.9-08-05-012-L
2 F
T1 Zero Loss
Codec
T1 / IP
Gateway
Circuit
“A”
Loop Start / IP
Gateway
IP-Based Telephone
Under Test
10/100/1000
Base-T
Ethernet
Hub
Telephone Handset
Receiver
Artificial Ear
& Microphone
Analog Telephone
IP Terminal
Adapter
Circuit
“B”
Microphone
Amplifier
Level
Recorder
Frequency Selective
Voltmeter
Figure 15.2-4 Setup for testing 47 CFR, 68.317 HAC volume control for IP-based
Telephone
19