[Speex-dev] Voice activity detection

zmorris at mac.com zmorris at mac.com
Fri Feb 15 19:08:13 PST 2008

On Feb 15, 2008, at 2:09 PM, Jean-Marc Valin wrote:

>> Anyway, my request is, can you build in a pre and post buffer into  
>> the
>> VAD?  In mine, if I detect voice any time between now and say a  
>> quarter
>> second later, I start sending, and then I wait a half second or  
>> whatever
>> after I stop detecting.  You pretty much have to have this, or people
>> start getting anxious talking over an internet stream.  They have to
>> enunciate expressions like "ya probably" because the ya isn't  
>> detected,
>> only the probably.  By sending a bit of padding around the  
>> detection, it
>> also prevents the detector from dropping out mid-sentence.  It  
>> takes it
>> from being a screaming contest over a walkie talkie, to a normal
>> telephone conversation.
>> You might be reluctant to do this, because you have to add in some  
>> state
>> information instead of just focusing on the current buffer, but the
>> quality improvement is enormous.  I'd just like to be able to pass  
>> a pre
>> and post value to the VAD in milliseconds, defaulting to either 0 or
>> values similar to what I quoted above.  And I realize this can add  
>> some
>> delay, but even detecting a single extra syllable makes a world of
>> difference.
> If you like to buffer speech, just do it. There's no reason you need  
> to
> have the buffer in the VAD itself.

Well, what I am actually asking for is to have the VAD report  
detection a little before and after the sound.  This is pretty easy  
conceptually, but really messes up the code if every single user has  
to re-create it.  I faked it by just queuing up a FIFO of buffers, and  
if the VAD detects something, I begin sending a little before that  
point, and then I continue sending a little after.  I know this is old  
hat for the devs hear, but this is a pretty complex thing for joe  
blow, and honestly I don't see many people ever doing it.  People may  
get the perception that they really have to enunciate to get speex to  
work, but that's due more to the VAD's approach than to any limitation  
in speex itself.


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