[Freeswitch-users] Better results from mod_vmd

[Eric des Courtis]

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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