Proposed Conversational Gain Addendum for TSB-31-D
Whitesell Consulting LLC
Stephen R Whitesell
2 Shannon Ct
Howell, NJ 07731-8919
Phone: 732 751 1079
Intended Purpose of Document
For Incorporation Into TIA Publication
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 220.127.116.11 through 18.104.22.168 inclusive of the TIA Engineering Committee Operating Procedures dated May 2014, all of which provisions are hereby incorporated by reference.
It has been three years since TIA filed its petition (October 25, 2012) with the FCC to adopt the ANSI/TIA-4965 Conversational Gain standard into Part 68.317 of its rules to replace the severely outdated standards cited for measuring receive volume control as a change in ROLR level. TR-41.9 previously prepared and approved an addendum to TSB-31-D providing test procedures for showing compliance with ANSI/TIA-4965 (see TR41.9-13-09-007-MR1). Publication of the addendum was withheld until such time as the FCC issued an NPRM on adopting the standard. Authorization to publish was later withdrawn when it became desirable to go ahead with a different addendum that relied on some of the material contained in the approved text. The necessary material was transferred to the new addendum and the revised addendum for conversational gain (see TR41.9-14-08-007) was placed on hold.
Since the FCC had not yet issued an NPRM for adopting ANSI/TIA-4965, this addendum was prepared by the approach of adding conversational gain test procedures to TSB-31-D as a new Appendix F. It completely replaces the existing sub-clause 14.2 on volume control with new text that consolidates the original 14.2 text with the changes made to it by Addendum 1, which is thereby superseded. The new text also contains pointers to the new Appendix F and includes the statement that compliance with its conversational gain requirements is sufficient for demonstrating compliance with the existing Part 68.317 requirements.
This -LR1 revision was created because the FCC finally released the NPRM for adopting ANSI/TIA-4965 on October 30, 2015. A few tweaks have been added to take that into account.
Formulated under the cognizance of TIA Subcommittee TR-41.9
Technical and Administrative Regulatory Considerations
With the concurrence of TIA Engineering Committee TR-41
Performance and Accessibility for Communications Products
Table of Contents
2.MODIFICATIONS TO Existing tsb-31-d Text 9
3.Replacement Text for Sub-clause 14.2 10
4.Text for New Appendix F 15
FOREWORD (This foreword is not part of this Standard.)
This document is an addendum to TIA TSB-31-D, Telecommunications – Telephone Terminal Equipment – Rationale and Measurement Guidelines for U.S. Network Protection. It was developed to implement the use of conversational gain test procedures as described in ANSI/TIA-4965 for showing compliance with the receive volume control requirements in 47 CFR 68.317. It supersedes the information provided in TIA TSB-31-D-1 (Addendum 1).
This addendum was produced by Subcommittee TR-41.9, Technical and Administrative Regulatory Considerations. It was developed in accordance with TIA procedural guidelines, and represents the consensus position of the Subcommittee, which served as the formulating group. It also received the concurrence of Engineering Committee TR-41, Performance and Accessibility for Communications Products.
The leadership of the TR-41.9 Technical and Administrative Regulatory Considerations Subcommittee (Interim Chair: Jason Nixon, Industry Canada) acknowledges the written contributions provided by the following individuals in the development of this addendum.
Whitesell Consulting LLC
Stephen R Whitesell
Cisco Systems, Inc.
Suggestions for improvement of this standard are welcome. They should be sent to:
This addendum provides changes to TSB-31-D, Telecommunications – Telephone Terminal Equipment – Rationale and Measurement Guidelines for U.S. Network Protection. It supersedes the TSB-31-D-1 addendum to the above document.
Clause 2 of this document provides changes to clause 3, REFERENCES and to sub-clause 5.5, Suggested Equipment List (SEL) of TSB-31-D.
Clause 3 of this document provides completely new text for sub-clause 14.2 of TSB-31-D on test procedures for receive volume control. The new text incorporates the changes to the original text of sub-clause 14.2 that were made by TSB-31-D-1 and adds additional text referencing conversational gain test procedures in accordance with ANSI/TIA-4965.
Clause 4 of this document provides the actual conversational gain test procedures in the form of a new Appendix F to be added to TSB-31.D.
The other clauses and sub-clauses in TSB-31-D are not affected.
For the changes provided in Clause 2, additions to the text are shown underlinedand deletions are shown using strikeout. The new text provided for sub-clause 14.2 in Clause 3 is a complete replacement for the existing text and is not otherwise marked. Likewise, the completely new Appendix F text in Clause 4 is not otherwise marked. Words that appear in underlined italicsare intended as instructions to the reader.
For the changes provided in Clause 2, additions to the text are shown underlined and deletions are shown using strikeout. The new text provided for sub-clause 14.2 in Clause 3 is a complete replacement for the existing text. Changes resulting from combining that existing text with the text previously provided in Addendum 1 are not marked. Only the additional changes made by this Addendum are shown using underlining and strikeout. Likewise, the completely new Appendix F text in Clause 4 is not otherwise marked. Words that appear in underlined italicsare intended as instructions to the reader.
2.MODIFICATIONS TO Existing tsb-31-d Text
Changes to clause 3, REFERENCES
Add the following references to Section 3:
ANSI/TIA-4965-2012, Telecommunications – Telephone Terminal Equipment – Receive Volume Control Requirements for Digital and Analog Wireline Handset Terminals
IETF RFC 3551 (2003), RTP Profile for Audio and Video Conferences with Minimal Control
ITU-T Recommendation G.722 (2012-09), 7 kHz audio-coding within 64 kbit/s
Changes to sub-clause 5.5, Suggested Equipment List (SEL)
Modify item (74) as follows:
(74) G.711 Reference codec: A zero-level encoder/decoder pair providing analog-to-digital and digital-to-analog conversion in opposite directions of transmission in the same piece of equipment whose performance approaches the ideal characteristics for conversion to and from the bit format appropriate for the digital interface under test and meets the requirements for a zero level decoder in TIA-968-B. Characteristics such as attenuation versus frequency distortion (frequency response), idle channel noise, and quantization distortion should be considered. For example, ideal characteristics for PCM codecs are described in ITU-T Recommendation G.712.
Add items 78 and 79 as follows:
(78) L16-256 reference wideband linear, sixteen bit, 256 kbit/s codec. See IETF RFC 3551 and ANSI/TIA-4965.
(79) ITU-T G.722 reference wideband codec (0 dBm0 = 9 dB below full scale).
3.Replacement Text for Sub-clause 14.2
Replace sub-clause 14.2 in its entirety with the following:
Hearing Aid Compatibility - Volume Control 47 CFR, 68.317
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. 47 CFR, 68.317 cites industry standards dating back to 1987 for its volume control specification. A modified version of those requirements is discussed as an alternative method in 14.2.6.
An entirely new volume control measure, known as Conversational Gain, is discussed in Appendix F. Compliance with the Conversational Gain requirements is sufficient for showing compliance with the existing 47 CFR, 68.317 requirements.
The FCC has released an NPRM for adopting Conversational Gain into 47 CFR, 68.317 to replace the current receive volume control requirements. They have proposed to allow a two-year transition period during which compliance with either the either the old or new requirements will be acceptable. After that transition period ends, the testing guidance provided in sub-clause 14.2 will become obsolete and only the guidance provided in the new Appendix F will apply.
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. Procedures are provided for both telephones with an analog interface (analog telephones) and for telephones with a digital interface (digital telephones).
(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) Reference codec SEL#74.
Note: Refer to subclause 5.5 for equipment details.
Equipment States Subject To Test
Normal off-hook talking condition.
Connect the telephone under test as shown in Figure 14.2-1 for analog telephones and as shown in Figure 14.2-2 for digital 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.
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.
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.
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.
The generator output is to be adjusted to an open circuit voltage of 0.316 volt (i.e., -10 dBV) from a 900 ohm source for analog telephones. For digital telephones apply a signal level of -16 dBm0 to the input of the reference codec.
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) 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.
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.
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 digital telephones since the receive level is independent of loop length.
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 22.214.171.124 of ANSI/TIA-579 for digital 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.
Adjust the volume control of the telephone under test to its maximum volume setting and repeat steps (5) through (8).
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.
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 a level less than 18 dB above the normal unamplified level.
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.
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
This relationship was derived from measurements of the G-type handset used on the Western Electric 500-type telephone and measured with an ITU-T Recommendation P.57 Type 1 artificial ear (IEC 318 coupler). The relationship may differ when testing other types of handsets that do not seal on the knife-edge of the Type 1 ear or when a Type 3.3 artificial ear with a flexible rubber pinna is used for the testing as required by current industry standards. In this case, both the ROLR and RLR values should be calculated from the same measured frequency response curve to determine the appropriate relationship between the two for the specific combination of handset geometry and artificial ear. The resulting relationship may then 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.
For digital telephones, the sinewave generator and reference codec may be replace by a means for directly generating a digital bit stream in the appropriate format that is equivalent to the digital bit stream that would be produced from the reference codec with the specified sinewave signal applied.
Also see Appendix F for an entirely new measure known as Conversational Gain that may be used to show compliance with the 47 CFR, 68.317 volume control requirements.
Also see Appendix F for an entirely new measure known as Conversational Gailn that may also be used to show compliance with the 47 CFR, 68.317 ROLR-based volume control requirements. At some point in the future, the use of Conversational Gain is expected to replace the ROLR method in 47 CFR, 68.317. When that occurs, the test methods described in 14.2 will no longer be applicable and the new procedures provided in Appendix F should be used.
Suggested Test Data
State the type of artificial ear used for the tests.
If the test results were determined as ITU-T P.79 RLR values, show those values and the conversion to ROLR values.
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 digital 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.
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.
If the gain at the maximum receive volume control setting exceeds 18 dB, state if the amplified receive capability automatically resets to a level less than 18 dB above the normal unamplified level when the telephone is forced to pass through a proper on-hook transition.
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.
This requirement applies to telephones with receive volume control.
ROLR is a loudness rating value expressed in dB of loss. More positive values of ROLR represent lower receive levels.
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 subjective listening test. If an objective measurement is used, greater than 10% total harmonic distortion might be considered significant clipping.
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 a level less than 18 dB above the normal unamplified level if certain warning information is provided. See FCC Memorandum Opinion and Order DA 01-578.
Note: The generator output is to be adjusted to an open circuit voltage of 0.316 V (i.e.,10 dBV) from a 900 ohm source.
FIGURE 14.2-2 SETUP FOR TESTING 47 CFR, 68.317 HAC VOLUME CONTROL
FOR DIGITAL TELEPHONES
4.Text for New Appendix F
Add a new Appendix F as follows:
APPENDIX F, CONVERSATIONAL GAIN, AN ALTERNATIVE VOLUME CONTROL MEASURE
In 1996 the Commission adopted rules for volume control based on Receive Objective Loudness Rating (ROLR) values as specified in two industry standards: ANSI/EIA-470-A-19087 for analog telephones and ANSI/EIA/TIA-579-1991 for digital telephones. Although the analog standard has been revised or amended four times and the digital standard has been revised or replaced by a new standard five times, the 47 CFR, 68.317 rules have never been updated.
The changes in the industry standards have included replacing the Type 1 artificial ear (IEC 318 coupler), which has a circular knife-edge interface on which most modern handsets do not properly seal, with a Head and Torso Simulator (HATS) using a Type 3.3 human pinna simulator made of rubber that is appropriate for all types of handsets. They have also included replacing the IEEE Std 661-1979 based ROLR measure with an ITU-T Recommendation P.79 based Receive Loudness Rating (RLR) measure. These changes are reflected in the alternative method provided in 14.2.6.
The outdated industry standards currently cited in 47 CFR, 68.317 cover a whole gamut of performance issues related to telephones, only a small portion of which are relevant to the specification of receive level and receive volume control. To address this issue and to take advantage of a better measure for receive volume control known as Conversational Gain, TIA developed a new standard, ANSI/TIA-4965-2012. Simply stated, conversational gain is the measure of how loud speech sounds relative to a normal face-to-face conversation at a distance of 1 m. TIA has petitioned the FCC to adopt this new standard into 47 CFR, 68.317 in place of its existing outdated volume control requirements.
The current 47 CFR, 68.317 volume control requirements have three major aspects:
(1) A requirement that the ROLR level at the normal unamplified volume control setting of the handset or headset comply with limits specified in the cited industry standards. These tolerance limits allow the actual ROLR level to be as much as 5 dB belowquieter than the specified mean level.
(2) A requirement to provide at least 12 dB of gain as measured by the change in ROLR level between the normal unamplified level and the maximum volume control setting. This gain is to be provided without causing significant clipping of the test signal.
(3) If the maximum gain exceeds 18 dB, a requirement to reset the gain to a level less than 18 dB when the telephone is caused to pass through a normal on-hook transition.
Item (1) above allows the possibility of biasing the ROLR for the normal unamplified level toward the low quieter side of the allowed tolerance in order to more easily meet the 12 dB gain requirement without significant clipping. The TIA-4965 standard eliminates this possibility by defining the normal unamplified acoustic output level as 76 dBSPL for single ear listening. This value corresponds to 6 dB of conversational gain and is based on measurements of the typical output level of Western Electric 500-type telephones and their corresponding GTE model 80 counterpart. None of these telephones have volume controls, but their ROLR values are near the mean level cited in the referenced ANSI/EIA-470-A-19087 standard (see Annex A.6 of TIA-4965). This is the “nominal” value for the “normal unamplified level” to which 47 CFR 68.317 refers.
Since the 76 dBSPL normal unamplified level of these older reference telephones without volume controls corresponds to 6 dB of conversational gain, the 47 CFR 68.317 requirement to provide 12 dB of gain above this level corresponds to a conversational gain of 18 dB. Likewise, the 47 CFR, 68.317 requirement to reset the volume control when the gain exceeds 18 dB corresponds to 24 dB of conversational gain.
To determine that the receive volume control of a telephone with a handset or headset meets the following ANSI/TIA-4965 requirements when tested using conversational gain as the loudness measure:
(1) Provide at least 18 dB of conversational gain without causing significant clipping of the test signal.
(2) If the maximum conversational gain exceeds 24 dB, to reset the conversational gain to a level less than 24 dB when the telephone is caused to pass through a normalproper on-hook transition.
If the telephone complies with these requirements, it complies with the 47 CFR 68.317 requirement to provide 12 dB of gain above a normal unamplified level that has an ROLR within the limits specified in the cited ANSI/EIA-470-A-19087 and ANSI/EIA/TIA-579-1991 standards, to do so without significant clipping, and to reset the gain if it is more than 18 dB above the normal unamplified level. Procedures are provided for both telephones with an analog interface (analog telephones) and for telephones with a digital interface (digital telephones).
(1) Signal source with IEEE Std 269 real male speech SEL#75.
(2) Real-Time Analyze SEL#77.
(3) Head and Torso Simulator (HATS) SEL#76.
(4) Type 3.3 Artificial ear SEL#69.
(5) Microphone amplifier SEL#53.
(6) Test loop or commercially available artificial loop equivalent to 2.7 km #26 AWG non-loaded cable SEL#50.
(7) G.711 Reference codec SEL#74.
(8) L16-256 Reference codec SEL#78.
(9) G.722 Reference codec SEL#79.
Note: Refer to subclause 5.5 for equipment details.
F.4 Equipment States Subject To Test
Normal off-hook talking condition.
The measurement methods for receive volume control for both analog and digital telephones are in clause 4.4.2 of ANSI/TIA-4965-2012.
F.6 Alternate Methods
F.7 Suggested Data
(1) If the EUT is a wideband digital telephone, state the type of codec used.
(2) State the measured dBSPL.
(3) State the calculated conversational gain as defined in ANSI/TIA-4965.
(4) If the conversational gain at the maximum receive volume control setting exceeds 24 dB, state if the amplified receive capability automatically resets to a level of 24 dB or less when the telephone is forced to pass through a proper on-hook transition.
(5) State whether significant clipping was detected at the maximum gain setting. If so, state if there was a lower volume control setting that provided at least 18 dB of conversational gain without producing significant clipping.
(1) This requirement applies to telephones with receive volume control.
(2) The measurement is done with the telephone’s volume control set to the maximum.
(3) Test circuits for analog telephones are in clause 4.2 of ANSI/TIA-4965-2012.
(4) Test circuits for digital telephones are in clause 4.3 of ANSI/TIA-4965-2012.
(5) The sound pressure as measured by the HATS artificial ear is translated to free field conditions.
(6) Conversational gain is calculated by subtracting 70 dB from the measured dBSPL.