Re: Pathetic audio at 28.8 on Mac

Jan Engvald LDC (Jan.Engvald@LDC.lu.se)
Fri, 07 Apr 1995 12:26:12 +0200


>>...28.8 kbs modem...Audio STINKS
>
>This is a known feature of audio over low-bandwidth links, such as modems.

The Intel DVI 32 kb/s audio, which is the default for CU-SeeMe,
loads a link to a lot more than 28.8 kb/s. So even if you close
the video window and just listen to the sound, there will be dropped
packets causing interruptions and timing problems with the audio.
If you look at the video too, it will be worse.

>The delta-mod compression works for some folks, but not for others.

The delta-mod "16 kb/s" audio actually produces 21 kb/s data. Then
add UDP and IP headers and it will just fit into 28.8 kb/s (V.34).

BUT: You are not shure you get 28800 bps, often you get one step
down, i e 26400 bps. I have found that this small change is enough
to casue some interruptions in the audio. Note, that even if you get
28800 bps speed when you connect, this can dynamically be lowered
(and rised) during the time of the connection.

Also note that it is the SENDER that has the choice of selecting
among the different audio compression versions, the receiver can
do nothing about it.

What the receiver can do is to choose if he wants to receive video,
audio or video+audio (however, the current PC version 0.34b4 requests
audio even though it can not play it, so you always overloads a
modem link; the next version will be better).


Jan Engvald, Lund University Computing Center
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