Couple of issues: 1/ we don't want the codec to break down when the input audio is corrupted by tones and/or noise, or various other impairments like poor quality audio, echo, a siren, two voices etc. By "break" I mean render the wanted speech signal unintelligible or horrible to listen to. This is DSP problem with no impact on the bit rate.
2/ In some cases (e.g. DTMF, PSTN call progress tones), we would like to faithfully reproduce the tones at the output of the codec. In this case faithful reproduction of input speech is not required for the duration of the tone (we don't talk while we a dialing). This requires a trivial increase in the bit rate, like 1 bit/frame to say "this a DTMF frame or a speech frame". You then have every other bit at yr disposal to describe the tone for that frame - plenty. 3/ A corner case might be audio from an emergency services vehicle, where we would like to hear the siren in the background (perhaps at reduced level) as well as the voice of the person speaking. - David On 05/11/15 07:24, Bruce Perens wrote: > The difference between Codec2 and those older codecs for which mixed > tone and voice tests were written is that Codec2 is a pure voice codec. > That's one reason that Codec2 has so much lower bandwidth. I've gotten a > few tones through it, but only ones that sound like a voice. > > On Wed, Nov 4, 2015 at 12:13 PM, Steve <[email protected] > <mailto:[email protected]>> wrote: > > Well, disregard my last, as I was only thinking of DTMF tones, not > the tones you are describing. > > > > ------------------------------------------------------------------------------ > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > <mailto:[email protected]> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > ------------------------------------------------------------------------------ > > > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
