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