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

The distinction between use case and testing makes sense to me.

DTMF is a real use case. For example some PSTN gateways still don't  
support out-of-band DTMF.

It's unclear what to test about DTMF though. The Codec will support a  
range of sample rates and bitrates. The requirements specify coding of  
music at near-transparent quality. I don't see how a such a codec  
could not provide sufficient quality for in-band DTMF. At the same  
time, the requirements talk about bitrates down to 8 kbps, where it  
may be quite tricky to get DTMF to work well. Therefore, specifying  
that the codec SHOULD or MUST encode DTMF with sufficient quality is  
meaningless. If anything, the bitrate settings that allow in-band DTMF  
could be characterized after the Codec is formed.

Nevertheless it's good to be aware of these use cases during  
development. For instance, with SILK we included DTMF signals in the  
LSF quantizer training database.

Similarly, I see tandem coding as a use case to keep in mind during  
development, but again don't see a need for testing or MUST/SHOULD  
requirements.

koen.

Quoting stephen botzko:

> I agree that there is a pretty strong consensus that carriage of "analog"
> fax and modem signals is a non-requirement.  If by "payload switching" we
> are talking about switching codecs, then that is beyond the charter scope.
>
> I am thinking that we are getting a bit too focused on testing methods.  In
> my view it would be more efficient to capture use cases, and derive MUST and
> SHOULD requirements from them first.  Then go back and figure out what we
> will test and how we will test it.
>
> Stephen Botzko
>
>
>
> On Tue, Apr 6, 2010 at 7:47 AM, Kevin P. Fleming <kpfleming@digium.com>wrote:
>
>> 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
>> 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
>> skype: kpfleming | jabber: kfleming@digium.com
>> Check us out at www.digium.com & www.asterisk.org
>>
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