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[Freeswitch-users] Better results from mod_vmd

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mattdfong at gmail.com
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Posted: Thu Aug 20, 2009 7:41 pm Post subject: [Freeswitch-users] Better results from mod_vmd

I changed

/*! Minimum time for a beep. */
#define MIN_TIME 8000

to 6500 and it seemed to work, but I'm not sure how many false positives I will get in a real-world environment. at 4000 it fired the event like 5 times in a session, but 6500 only once. Do you think I should expect a lot of false positives after changing this value?

--matt
http://www.hellohunter.com

On Thu, Aug 20, 2009 at 4:54 PM, Eric des Courtis <eric.des.courtis@gmail.com (eric.des.courtis@gmail.com)> wrote:

Quote:

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@gmail.com (eric.des.courtis@gmail.com)> wrote:

Quote:

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@freeswitch.org (msc@freeswitch.org)> wrote:

Quote:

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

Quote:

On 08/20/2009 05:22 AM, Michael Collins wrote:

Quote:

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. Smile

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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eric.des.courtis at gm...
Guest

Posted: Thu Aug 20, 2009 9:02 pm Post subject: [Freeswitch-users] Better results from mod_vmd

Matt,

I think the only way to know for sure is to try it. I would try to get
the value as high as possible while still detecting that 738Hz sine
(with a small margin of error). Lowering the value increases false
positives rapidly.

Eric des Courtis

On Thu, Aug 20, 2009 at 8:36 PM, Matthew Fong<mattdfong@gmail.com> wrote:

Quote:

I changed

/*! Minimum time for a beep. */
#define MIN_TIME 8000
to 6500 and it seemed to work, but I'm not sure how many false positives I
will get in a real-world environment. at 4000 it fired the event like 5
times in a session, but 6500 only once. Do you think I should expect a lot
of false positives after changing this value?

--matt
http://www.hellohunter.com

On Thu, Aug 20, 2009 at 4:54 PM, Eric des Courtis
<eric.des.courtis@gmail.com> wrote:

Quote:

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

Quote:

On 08/20/2009 05:22 AM, Michael Collins wrote:

Quote:

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. Smile

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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gabe at gundy.org
Guest

Posted: Thu Aug 20, 2009 10:23 pm Post subject: [Freeswitch-users] Better results from mod_vmd

On Thu, Aug 20, 2009 at 6:36 PM, Matthew Fong<mattdfong@gmail.com> wrote:

Quote:

/*! Minimum time for a beep. */
#define MIN_TIME 8000
to 6500 and it seemed to work, but I'm not sure how many false positives I
will get in a real-world environment. at 4000 it fired the event like 5
times in a session, but 6500 only once. Do you think I should expect a lot
of false positives after changing this value?

YES.

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UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
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gabe at gundy.org
Guest

Posted: Thu Aug 20, 2009 10:25 pm Post subject: [Freeswitch-users] Better results from mod_vmd

On Thu, Aug 20, 2009 at 9:16 PM, Gabriel Gunderson<gabe@gundy.org> wrote:

Quote:

On Thu, Aug 20, 2009 at 6:36 PM, Matthew Fong<mattdfong@gmail.com> wrote:

Quote:

YES.

Err, NO.

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