[Freeswitch-users] Better results from mod_vmd

[Eric des Courtis]

Matt,

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.

Cheers.

Eric des Courtis


On Thu, Aug 20, 2009 at 7:51 PM, Eric des
Courtis<eric.des.courtis at gmail.com> wrote:
> Matt,
>
> For your information the tones you gave me are exactly 738Hz. If you
> want to try that tone detection thing.
>
> Cheers.
>
> 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>
>> 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.
>>
>> -MC
>>
>>
>>
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>