TR-41.3.3/99-05-003
TITLE:
Project:
CONTACT:
DATE:
Homework: Ref Codec, Loudness Ratings, Handsfree
PN-4352
Ron Magnuson - Siemens
1-512 - 990 - 6097
Fax: 6342
ron.magnuson@ieee.org
5 May 99 (For Portland Meeting)
(Updated 10 May 99 with STMR corrections and improved drawings)
Abstract:
Document contains:
New drawings and text regarding Reference Codec.
Equations for Loudness Rating Calculation.
Calculation of transmit and receive frequency response.
Suggested Handsfree volume control range and loudness ratings.
NOTICE: The proposals in this submission have been formulated to assist Subcommittee TIA TR-41.3.3. This
document is offered to the subcommittee as a basis for discussion and is not binding on Siemens. Siemens
specifically reserves the right to add to, or amend, the quantitative statements made herein. Nothing contained
herein shall be construed as conferring by implication, estoppel, or otherwise any license or right under any patent,
whether or not the use of information herein necessarily employs an invention of any existing or later issued patent.
The contributor grants a free, irrevocable license to the Telecommunications Industry Association (TIA) to
incorporate text contained in this contribution and any modifications thereof in the creation of a TIA standards
publication; to copyright in TIA’s name any standards publication even though it may include portions of this
contribution; and, at TIA’s sole discretion, to permit others to reproduce in whole or in part the resulting TIA
standards publication.
1
Contribution for Section 4.3 Reference CODEC
A codec approaches an ideal codec and has superior, well-defined characteristics. A
reference codec is used for testing digital telephone terminals with analog test equipment.
When a 0 dBm (0.775 volt) analog signal is applied to the coder input a 0 dBm0 digital level is
present at the digital reference.
When a 0 dBm0 digital level is applied to the decoder a 0 dBm analog signal appears at the
decoder output.
This implementation of a reference codec eliminates the 600 ohm source and load resistors
specified by other standards. The Coder input impedance is high relative to the generator and
the decoder output impedance is low relative to the measuring voltmeter.
NOTES TO EDITOR:
1. Visio file supplied. Image is pasted here for convenience.
2. Sm and Se are replaced by PM and PE. S is sensitivity (V/Pa or Pa/V) P is sound
pressure.
3. This drawing may be generic enough to be used as a base for all test setup
drawings handset, headset, handsfree receive, send, sidetone, TCL etc.
Digital Reference
Point
(Junction j)
Send
pM
v
Decoder
Mouth Sound
Pressure
Digital
Set
Interface
pE
Ear Sound
Pressure
vSEND
Coder
Receive
vRCV
Reference Codec
Figure 1 – Digital Telephone Set Test Arrangement with Reference Codec
2
Contribution for Section 5.1.1: Handset Send Frequency Response (Sensitivity)
Note to Editor: Propose to add the following text:
Send frequency response (Send sensitivity) is the ratio of the voltage output of the reference codec to the sound
pressure at the Mouth Reference Point (MRP) for each frequency or frequency band (Fi) as shown in the equation
below:
SMJ = 20 log (VSEND / PM)
dB rel 1 V / Pa
Where
SMJ
PM
VSEND
= Send Sensitivity, Mouth to Junction, at frequency Fi .
= Sound pressure at the MRP at frequency Fi.
= RMS output voltage of the reference codec at frequency Fi
The handset shall be mounted in the LRGP (Loudness Guard-Ring Position).
Measurements should be done in 1/12 octave intervals or smaller.
Contribution for Section 5.1.2 Handset Receive Frequency Response (Sensitivity)
Note to Editor: Propose to add the following text:
Receive frequency response (Receive sensitivity) is the ratio of the sound pressure measured in the ear simulator to
the voltage input to the reference codec for each frequency or frequency band (Fi) as shown in the equation below:
SJE = 20 log (PE / VRCV) dB rel 1 Pa / V.
Where
SJE
PE
VRCV
= Receive Sensitivity, Junction to Mouth, at frequency Fi.
= Sound pressure measured by ear simulator at frequency Fi.
= RMS Input voltage to the reference codec at frequency Fi
Measurements should be done in 1/12 octave intervals.
3
Contribution: Calculation of Loudness Ratings
NOTE to Editor: It may be clearer to add these equations to the document as well as referring
to P.79 (Maybe as an appendix). The equations are specific to this document.
Send Loudness Rating:
Band 17
SLR = - 57.1 log10

10(0.1 * 0.175 * (SMJ - Wsi)
i = Band 4
Where:
SMJ
Frequency bands from Table 1 of ITU_T P.79-1993, bands 4-17.
Send Frequency response data (Sensitivity, Mouth to Junction) in dB V/Pa
measured per this standard.
Wsi
Send weighting factor from Table 1 of ITU-T P.79-1993.
i
Receive Loudness Rating:
Band 17
RLR = - 57.1 log10

10(0.1 * 0.175 * (SJE - Wri - LE )
i = Band 4
Where:
SJE
Frequency bands from Table 1 of ITU_T P.79-1993, bands 4-17.
Receive Frequency response data (Sensitivity, Junction to Ear) in dB Pa/V
measured per this standard.
Wri
Receive weighting factor from Table 1 of ITU-T P.79-1993.
LE
Leakage correction from Table 2 of ITU-T P.79-1993. Only used when handset is
sealed to IEC-318 ear. Not used with Handsfree, Headsets, or when using ear
simulators with controlled leakage.
i
Sidetone Masking Rating:
Band 20
STMR = - 44.4 log10

10(0.1 * 0.225 * (SmeST - WMSi)
i = Band 1
Where:
SmeST
Frequency bands from Table 3 of ITU_T P.79-1993, bands 1-20.
Sidetone Frequency response data (Sensitivity, Mouth to Ear) in dB Pa/Pa
measured per this standard.
WMSi
Sidetone weighting factor from Table 3 of ITU-T P.79-1993.
i
4
HOMEWORK: HANDSFREE VOLUME CONTROL
I’d like to investigate this further but based on testing of four ISDN telephones, the following
seems appropriate:
RLR – Default Volume Control
RLR – Maximum Volume Control
RLR – Minimum Volume Control
Volume Control Range
SLR
5
2 dB
- 6 dB or louder
18 dB or quieter
>= 24 dB
15 dB