[Freeswitch-users] Better results from mod_vmd

Michael Collins msc at freeswitch.org
Thu Aug 20 11:20:17 PDT 2009

On Thu, Aug 20, 2009 at 11:06 AM, Steve Underwood <steveu at coppice.org>wrote:

> On 08/20/2009 05:22 AM, Michael Collins wrote:
> >
> >     There is no noise on those 3 beeps. In fact, for something that's
> been
> >     through ulaw/alaw compression those beeps are very clean. They are
> >     quite
> >     short, though.
> >
> >
> > Heck yeah they're short! Steve, in your experience is there a
> > practical way to detect a beep that short without chewing up system
> > resources or having lots of false positives?
> > -MC
> >
> The tone samples I just looked at are about 130ms long. The problem is
> the detector is trying to be a very open ended detector of anything
> narrowband enough to be a single tone, and of any duration beyond some
> small minimum. Its difficult to make such a thing voice immune unless
> you can also count on a very large signal to noise ratio. With a digital
> trunk you can probably rely on a large SNR, but what happens when people
> use analogue lines? There is a reason why DTMF detectors try hard to
> work down to about 10dB SNR. :-)
> Steve

Thanks for the lesson uncle Steve! I'm guessing that the OP will need a new
strategy. Possibly waiting for silence? Not sure what's the best way to go
but I'm interested in hearing if someone has a solution.

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