TELECOM Digest OnLine - Sorted: Re: Invalid Number Tones

Re: Invalid Number Tones

L Hao (
Thu, 3 Feb 2005 11:25:08 -0800

Thanks Brad and other responders. Really helpful. It does sound like a
telemarketing system, doesn't it? : ). Well, it is not. I got people
asking me the same question in the DSP thread. It is a system for our
Pharmacy and Clinic customers to remind their patients more

Brad Houser <> wrote in message

> L. Hao <> wrote in message

>> I need to design an algorithm to detect call progress. For example, it
>> needs to figure out whether the call hits a live person, an answering
>> machine, a fax machine, and etc. But among all these things, I am
>> having trouble finding the spec for this so-called invalid
>> number. When you dial an invalid number, you normally get a tone
>> followed by " the number you just dialed ...".

>> Can anyone tell me where I can find the spec for this tone? Or
>> better yet, if anyone can share his/her methods of detecting it,
>> it'd be great.

> The Special Information Tone (SIT) is 950, 1400, 1800 (all tones +-
> 50 for 330 +- 70 ms.

> Brad Houser

[TELECOM Digest Editor's Note: Also see the other message in this
issue from Lisa Hancock talking about telemarketers who bother her
household at inconvenient times, etc. If nothing else, you can
measure these tones yourself using a device intended to scare away
the telemarketers. Inquire of

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