Voice Signal Level in H323 Terminal/Gateway

Sakae OKUBO okubo at GITI.WASEDA.AC.JP
Mon Jul 3 22:09:36 EDT 2000


At 14:14 -0400 00/06/30, Shan Lu wrote:

>I'd like to start a discussion on how to set speech signal level in an
>H323 environment.

For the H.320 system, a similar situation arose. After the initial version
of H.320 had been approved in December 1990, audio level setting problem
was raised and specifications were added in the March 1996 revision as
section 4.2.1 referring to P-series Recommendations. For your convenience
an excerpt is attached at the end of this message.

I hope this is also applicable to the H.323 system or becomes at least a
good starting point.

Best regards,

Sakae OKUBO
***********************************************************
Waseda Research Center
Telecommunications Advancement Organization of Japan (TAO)
5th Floor, Nishi-Waseda Bldg.
1-21-1 Nishi-Waseda, Shinjuku-ku, Tokyo
169-0051 Japan
       Tel: +81 3 5286 3830 (to be transferred)
            +81 3 3204 8194 (direct)
       Fax: +81 3 5287 7287
       e-mail: okubo at giti.or.jp
***********************************************************

Excerpt from H.320
(this has been converted to text from Word file)

4       Terminal requirements

4.1     Environments
Under study.

4.2     Audio and video arrangements

4.2.1   Audio arrangements

A terminal can have one or more of three different arrangements:

        - handset function;
        - handsfree function for a small group of users (up to three users);
        - handsfree function for more than three users (conference terminal).

The audio characteristics are defined for each of these functions.
Furthermore, the bandwidth of the transmitted speech is taken into
consideration.

The principles used are identical with those for telephony terminals. That
is, the sensitivity for handset function and handsfree function designed
for personal use or for a small group of users is specified in loudness
ratings, and the sensitivity for conference terminals is specified as
output levels.

4.2.1.1 Test principles

4.2.1.1.1       Handset function

The sensitivity measurement of a terminal when a handset is used shall be
based on the principles described in Recommendation P.64. The loudness
rating shall be calculated as described in Recommendation P.79.

4.2.1.1.2       Handsfree function for a small group of users

The sensitivity measurement of the handsfree function of a terminal
designed for a small group of users shall be based on the principles
described in Recommendation P.34. The applied test signal level at the
digital input when measuring receive sensitivity shall be -30 dBm0.

The user position for a visual telephone terminal depends on the design of
the terminal. The real user position as recommended by the supplier might
be different compared with the position used for measurements. A correction
factor shall be used. The correction factor is:

        F(dB) = 20 log10 {Ds/D0}

where Ds is the distance between the recommended user position and the
terminal and D0 is the reference distance of 50 cm.

The loudness rating shall be calculated as described in Recommendation P.79.

4.2.1.1.3       Handsfree function for a conference terminal

The principles described in Recommendation P.30 shall be used.

  4.2.1.2       Sensitivity

4.2.1.2.1       General

For handset terminals and handsfree terminals designed for a small group of
users, the sensitivity shall be specified as loudness ratings: Send
Loudness Rating (SLR) and Receive Loudness Rating (RLR). The definitions of
SLR and RLR are found in Recommendation P.10.

For conference terminals, the sensitivity shall be specified in terms of
input and output levels.

4.2.1.2.2       Receive volume control

For handsfree and loudspeaking terminals, a volume control shall be provided.

Where a manual receive volume control is provided, the minimum control
range shall be to -15 dB from the test position.
Where an automatic receive volume control is provided, the RLR value
obtained with a line level of -15 dBm0 shall not exceed that RLR value
which is obtained with a line level of -30 dBm0 by more than 15 dB.

4.2.1.2.3       Handset function

The requirements of Table 4 shall be met.

Table 4/H.320 - Sensitivity of the handset function
        3.1 kHz bandwidth(Note) 7 kHz bandwidth
SLR     8       8
RLR     2       7

NOTE - 3.1 kHz bandwidth includes both G.711 and G.728 coding.

The manufacturing tolerances are +/-3 dB.

4.2.1.2.4       Handsfree function

The requirements of Table 5 shall be met.

Table 5/H.320 - Sensitivity of the handsfree function
        3.1 kHz bandwidth(Note) 7 kHz bandwidth
SLR     13 - F  13 - F
RLR     -7 - F  -5 - F

NOTE - 3.1 kHz bandwidth includes both G.711 and G.728 coding.

The receive RLR requirement shall be met when the receive volume control is
in its maximum position. The manufacturing tolerances are +/- 4 dB.

4.2.1.2.5       Conference terminals

The procedures and values specified in Recommendation P.30 shall be used.

  4.2.2 Video arrangements

Under study.

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