Turn off VAD? (Voicing Activity Detection)

Posts: 76 · Vonage Forum Senior Joined: Oct 17, 2005 Posts: 76

Does anyone else find it a pain hearing the audio starting and stopping each time a person speaks? I'm talking about that fact that no audio whatsoever is passed when you (or the other party) are not speaking. Personally I can hear it coming in and out and it just bugs me a bit.

Anyone know if it can it be turned off? (i.e. Audio is transmitted all the time).

Posts: 282 · Posted: Fri Nov 11, 2005 12:25 pm Post subject:

Silence Suppresion is part of how VoIP works to limit bandwidth requirements. I'm not certain if all three codecs use it, but they propbably do. What Bandwidth Saver setting are you using (which is really a Codec selection)? I don't hear anything like you describe using the 90Kbps setting.

Posts: 605 · Posted: Fri Nov 11, 2005 12:59 pm Post subject:

I can sorta hear it with 90k and the volume cranked all the way up. Doesnt really bother me. If I turn the phone volume down it seems to go away.

Posts: 2257

bassplayer wrote:

Does anyone else find it a pain hearing the audio starting and stopping each time a person speaks? I'm talking about that fact that no audio whatsoever is passed when you (or the other party) are not speaking. Personally I can hear it coming in and out and it just bugs me a bit.

Anyone know if it can it be turned off? (i.e. Audio is transmitted all the time).

Doesn't particuarly bother me, though it is funny - occasionally I'll get someone on the other end saying "are you still there?" because the line went absolutely stone-cold silent. But that also happens with my GSM cell phone, and for the same reason. My breathing is not worth the bandwidth to transmit it. (grin)

Posts: 40 · Posted: Fri Nov 11, 2005 9:12 pm Post subject:

This maybe something they have to change once E911 fully rolls out.

Many times people have to wispher to the operator. Even if the VAD activates with wisphering..

Many times, it's huge help for 911 operators to hear breathing on the other end.

Just a thought,

Dan

Posts: 76 · Vonage Forum Senior Joined: Oct 17, 2005 Posts: 76

I'm on the 90k codec. Have to say, its sometimes more noticeable than others. It does make sense that you can save bandwidth by not transmitting silence but equally, if you cannot hold the sustained bandwidth required by the codec, you are going to experience poor audio quality anyway. Rather, I suspect this is for the benefit of reducing bandwidth requirements at the Vonage side of the connection. With thousands of users on calls at once, they get a sustained reduction in required bandwidth by only transmitting speech. Unless of course, everyone on a Vonage call speaks at the same time. (As an aside, I wonder if this contributes to occasional dip in voice quality I experience?!?! Can't really imagine it somehow given how high the number of users probably is - central limit theorum and all that). One thing I think is interesting here is that many phone lines using VAD also employ 'comfort noise'. This is a level of noise added artificially to a line to reassure callers that the connection is still active. Perhaps Vonage either don't use comfort noise or need to tweak it a little.

Posts: 37 · Vonage Forum Junior Joined: Nov 16, 2005 Posts: 37

VAD is definately NOT something that is required for VoIP to work. With the 30k setting, which is most likely the G729r8 codec VAD is probably turned off. G729 uses about 8k for voice. With the IP overhead and everything the packets come out to be around 26k. With VAD turned on you use a little bit less.

I would be very surprised if the 90k codec, or whatever they are calling G711ulaw has VAD turned on, that would just be silly. Easiest way to find out, do a packet capture on your ATA and look in the SIP SDP information.

Posts: 76 · Vonage Forum Senior Joined: Oct 17, 2005 Posts: 76

Interesting info Celeron - I'll have a look on my ipcop machine and see if I can see a dip in bit rate for silence.

If their is no VAD, perhaps the box just does some really nasty noise reduction which sounds like VAD to me. Worse still, perhaps their is a noise gate implemented which just cuts audio completely when the average audio signal falls below a certain level.

Posts: 37 · Vonage Forum Junior Joined: Nov 16, 2005 Posts: 37

I confirmed last night that the 30k "normal" bandwidth setting is in fact G729r8. Note, Vonage calls this "normal" quality. G729r8 is a very high compression codec. In actuality, the 90k setting, which is going to be the G711ulaw codec, is the "normal" setting. Your standard line from the telephone company has no compression, aka G711ulaw (or alaw if you live outside the US). If you truely want "normal" you need to use Vonage's "highest" quality setting.

Looks like VAD is off on the 30k setting. There really isn't any purpose in running it unless you are trying to conserve bandwidth across really slow WAN type connections. Its unfortunately that Vonage locks the users out of the voice settings on the ATAs because VAD has many configurable options that can make its presence undetectable.