[Asterisk-Dev] Voice energy detection: coder wanted

[Stephen Davies]

On Fri, 7 Nov 2003, John Todd wrote:

> I have a requirement from one of my customers (in the emergency 
> services arena, I am told) to develop a voice energy detection system 
> for Asterisk.  This would be to detect the difference between an 
> answering machine, and a human.  This detection need only be very 
> basic, and probably will hook into the existing routines in dsp.c 
> (unless you have a cadence and tonal module already built.)

So I'm curious as to the algorithms used.  All I can think of is that
an answering machine talks for longer than a real human caller.

dsp.c can already detect voice as opposed to various tones.  So
wouldn't answering machine detection go something like:

if <start detecting voice for the first time>
  note that the call is answered
  if you don't hear say 1sec silence within 5 secs then
    note that it was probably an answering machine

I'd allow the possibility that people talk "differently" when
recording an announcement - ie in "posh telephone voice" which perhaps
has a different spectrum to their usual voice - but seeing you dont
know their usual voice I'm not sure how you could use that.

Steve