From: tan (tan@dia.janis.or.jp)
Date: Fri Apr 04 2003 - 04:53:52 GMT-3
Scott, I had the same questions about VAD and comfort noise last week. The
confusing part at first was the similarity in the descriptions of sending
packets during times of silence with VAD or comfort-noise ect..
VAD is required to use the comfort-noise feature. Comfort-noise and a few
other features are a subset of VAD. VAD is Voice Activation Detector or
something like that. If you disable VAD, comfort-noise it disabled too along
with the other subset features.
Without VAD, your phone works like a normal analog phone, always "sending"
silent analog signals. So, if conversation has a pause, your router still
collects those empty analog signals, converts silent analog to digital,
packets them and sends off. With VAD and its voice detection turned on, the
router detects the silence and turns off the conversation so to speak, and
does not send the analog silent packets.
Next, comfort noise is a subset feature of VAD, the sending of a rumble to
give impression of open phone line. The other half of the feature is that
rumble would be annoying during the conversation, so it turns itself off
when speaking starts, and this is where the VAD part is necessary to
recognize when the speaking starts/stops.
Points...
VAD off equals same as analog conversation. Continual flow. No extra
features (like comfort-noise).
Vad on equals no "packets of silence" on the wire, less bandwidth used up,
traffic on wire is stop and go.
Comfort-noise equals packets of rumble on wire during silence. More
bandwidth than with both vad and comfort-noise turned off.
You can also tell when speaking that VAD is on, there is a micro second
delay in reverb back through the ear piece.
I experimented with comfort-noise, but my stack of routers were so loud in
the background it cancelled out any affect. Not to mention trying to talk to
yourself between two phones feels a bit foolish.
M
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Scott M. Livingston
> Sent: Wednesday, April 02, 2003 10:07 PM
> To: ccielab@groupstudy.com
> Subject: VOICE Feature Questions
>
>
> Anyone have any deep dark secrets on when and how best to use the
> following features? I don't have much practical experience in
> this area
> and no VIC's at the house. Basically, I am concerned with gotchya's
> related to these features.
>
> VAD
> COMFORT-NOISE
> MUSIC-THRESHOLD
>
> I understand the following:
>
> VAD: Configured on dial-peer only. On by default. When
> enabled it stops
> the sending of packets during silence. VAD should be enabled
> on low BW
> connections, but disabled for high BW links.
>
> COMFORT-NOISE: Configured on voice ports only. On by default. When
> enabled it is used to send "subtle" background noise during the silent
> periods.
>
> MUSIC-THRESHOLD: Configured on voice ports only. Not on by default???
>
>
> Question: VAD and COMFORT-NOISE seem to contradict one
> another. Or is it
> the fact that COMFORT-NOISE will send far LESS background
> noise compared
> to having VAD disabled? COMFORT-NOISE is just sending enough
> background
> noise to keep the listener on the other end happy in that they know
> someone is still on the line even if they stop speaking.???
>
> Thank You,
> scott
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