[Freeswitch-users] Better results from mod_vmd

Eric des Courtis eric.des.courtis at gmail.com
Thu Aug 20 16:51:01 PDT 2009


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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