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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. v1.0 – 20050426 Telecommunications Industry Association TR41.9-08-05-012-L 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. v1.0 – 20050426 Telecommunications Industry Association TR41.9-08-05-012-L 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. 3 Telecommunications Industry Association TR41.9-08-05-012-L 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. 4 Telecommunications Industry Association TR41.9-08-05-012-L (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. 5 Telecommunications Industry Association TR41.9-08-05-012-L (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. 6 Telecommunications Industry Association TR41.9-08-05-012-L (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 7 Telecommunications Industry Association TR41.9-08-05-012-L 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 8 Telecommunications Industry Association TR41.9-08-05-012-L 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 9 Telecommunications Industry Association 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 10 Telecommunications Industry Association 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 11 Telecommunications Industry Association TR41.9-08-05-012-L 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 12 Telecommunications Industry Association TR41.9-08-05-012-L 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. 13 Telecommunications Industry Association TR41.9-08-05-012-L (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 14 Telecommunications Industry Association TR41.9-08-05-012-L 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 15 Telecommunications Industry Association TR41.9-08-05-012-L 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 16 Telecommunications Industry Association TR41.9-08-05-012-L 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 17 Telecommunications Industry Association 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 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 18 Telecommunications Industry Association 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