Subject: [AVT] RFC 2833 tones payload and modulation

From: Tom Taylor <[email-masked]>
Date: Thu, 04 Dec 2003 09:46:11 -0500

The RFC 2833 tones payload type provides for both summation of 
frequencies and modulation by another frequency.  However, the 
modulation is missing a piece of information, because modulation of 
tones in practice isn't just a matter of multiplication.

My particular example is the V.8 ANSam tone.  This is modulated by a 15 
Hz envelope.  However, the specification of that envelope says that the 
amplitude of the total ANSam waveform varies from a minimum of 80% of 
the nominal value to 120%.

Obviously the payload description has been long established and it would 
be difficult to add the missing information now.  I see two alternatives:
   -- Recommend that modulation be applied the way it is for ANSam (i.e. 
with precisely the same 80% and 120% limits).  I'd justify this on the 
grounds that ANSam will be the most common case.  The other cases are 
tones intended for human consumption, so my second justifying argument 
is that using the ANSam boundaries might be close enough to what the 
tones have to sound like.
   -- Alternatively, recommend that the receiving gateway be aware of 
the nature of any tone presented with modulation, so it can construct 
the right envelope.

Any opinions, or is this something no one has implemented anyway?

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