[Freeswitch-users] Better results from mod_vmd
Eric des Courtis
eric.des.courtis at gmail.com
Thu Aug 20 16:54:52 PDT 2009
As is mod_vmd will not detect tones shorter then 138ms. However I
could get that value down to ~30ms at best by making a few
modifications to the algorithm.
Eric des Courtis
On Thu, Aug 20, 2009 at 7:51 PM, Eric des
Courtis<eric.des.courtis at gmail.com> wrote:
> For your information the tones you gave me are exactly 738Hz. If you
> want to try that tone detection thing.
> Eric des Courtis
> On Thu, Aug 20, 2009 at 2:20 PM, Michael Collins<msc at freeswitch.org> wrote:
>> On Thu, Aug 20, 2009 at 11:06 AM, Steve Underwood <steveu at coppice.org>
>>> 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. :-)
>> 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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