[Freeswitch-users] Detecting the origin of voice activity using VAD

[Steve Underwood]

Hi,

mod_vmd is a bit more sophisticated than that. It looks for the signal 
being narrowband energy. However, mod_vmd isn't very reliable, as it 
takes a rather high SNR for its narrowband detector to work. So high 
that a lossy codec like G.711 can barely manage it.

Regards,
Steve

Anthony Minessale wrote:
> i think that's what mod_vmd does
>
> On Mon, Mar 2, 2009 at 11:16 AM, Andy Spitzer <woof at nortel.com 
> <mailto:woof at nortel.com>> wrote:
>
>     Woof!
>
>     On Sun, 01 Mar 2009 21:28:18 -0500, Brian West
>     <brian at freeswitch.org <mailto:brian at freeswitch.org>> wrote:
>
>     > NO.  You want something that people THINK exists and works well...
>     > Reliable human/voice detection doesn't exist in ANY form.
>
>     I beg to differ.  See
>     http://www.freepatentsonline.com/5521967.html for one way to do
>     it.  It works rather well and can quickly descriminate between
>     voice and tone.  I've no idea who owns that patent now (not me,
>     for sure).
>
>     There is a simpler, less reliable way of differentiating voice
>     from tone, that as far as I know isn't patented.  If you compare
>     the RMS power levels of sequential 40 mS periods, call progress
>     tones will have very consistent power levels from sample to
>     sample.  So if 5 or more 40 mS periods have about the same power
>     measurement (within say, 2%), it's a tone.  Voice will have
>     dramatic power level differences over that same period.  This
>     works very well in today's telephony environment, where tones are
>     computer generated.  In the old days when ringback tone was
>     generated off the audio hum from the 20 Hz ring voltage
>     generator...not so well.
>
>     --Woof!
>
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