Dear Frank, All, > > > > TwinVQ is recommended by MPEG for bitrates of 6 Kbits/s where it showed > > performance of 8 Kbits/s MP3 - for higher bitrates TwinVQ might be worse > > (and it is, usually) than MP3. > > > The target of TwinVQ are bitrates between 24 and 64 kbit/s, not 6...8 kbit/s. > This very low bitrate range is target for CELP and other parametric codecs, > not for transformation based codecs. >
Sorry - my mistake, I was drawing conclusions from http://www.iis.fhg.de/amm/techinf/mpeg4/scalable.html [snip] MPEG-4 TwinVQ Coder An audio coder optimized for audio coding at ultra low bitrates around 8 kbps. Hierarchical coding (scalability) is also possible. [/snip] However, conclusions reported on W2776 MPEG document were clear, so Frank was right: On the material used in this test Twin VQ at 6 kbps performed worse than G.723.1 and NB CELP with the exception of some music items. TwinVQ is known to have lower quality for speech signals and also for speech+music, probably because speech signals are dominant when the bandwidth is limited below 4 kHz. Note that the TwinVQ under test directly quantizes input signals sampled at 24 kHz for the purpose of simple connection to AAC scaleable system. According to previous experience, it can be assumed that TwinVQ will achieve higher quality at the same bitrate if a lower sampling rate is used in the unscaled mode. > Also note that at such low bitrate the task is not to transmit audio, but > human voice, and it should be still possible to understand the human voice. > It can be sound fully different from the original, but it must be possible > to understand it. > > 5 kbps: CELP > 25 kbps: MPEG-2 AAC + SBR (MPEG-4 should be a little bit better) > 64 kbps: MPEG-2 Layer 3 + SBR > 96 kbps: MPEG-4 AAC MP > I would stay out of nonstandard extensions, like SBR - until they are (if!) accepted by MPEG. Regards, -- Ivan _______________________________________________ mp3encoder mailing list [EMAIL PROTECTED] http://minnie.tuhs.org/mailman/listinfo/mp3encoder
