Re: [codec] #5: Mention DTMF in requirements

["Kevin P. Fleming" <[e-mail]>]

Raymond (Juin-Hwey) Chen wrote:

> 2. Did you ever test your CODEC for other telephony signals, such as
> /ANSam, ANS, CED, and CI tones? These tones are needed in order to
> detect modems and fax machines and switch to an appropriate payload.
> What about progress tones?
> [Raymond]: No, we didn’t.  However, if these are single-frequency tones,
> I would expect that it should be easier for a typical codec to pass
> these tones than to pass the dual-frequency DTMF signals without causing
> significant degradation in the subsequent processing of these tones.

This is pretty much a dead-end based on the other comments on this list,
but in general, no, most of these tones are *not* single-frequency
simple tones. ANSam, for example, is a single frequency, but is
amplitude modulated. There are also variants that have phase reversals,
and these must be preserved for them to be discriminated from the
non-phase-reversal versions.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
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