> >
> > + maybe a MPEG2 vbr should get a Xing header?
> > at least optional via a switch?
> >
>
> Can you get Xing to generate a MPEG2 VBR file? I tried once and
> it aways produced fixed bitrate output files. The problem is the
> Xing header is embedded in a 64kbs frame, but at MPEG2 samplerates, a
> 64kbs frame is not large enough to hold the full Xing header.
> Probably should just go to a 128kbs frame for the Xing header,
> but I'd like to find out what Xing does first.
I don't have a Xing encoder. I mentioned it, because I like seeking
in a mp3. Without such a Xing header seeking would be impossible.
>
>
> > + finally, whats the dynamic range of a MPEG2 layer3
> > stream at 24, 22 and 16 kHz? Is it half the
> > dynamic range of a 44 kHz MPEG1 layer3 stream?
> > the MDCT scaling of the ath should consider this.
> >
>
> good point, and it should be tested. But I think it shouldn't change
> much: The MDCT transform takes as input 576 samples (both mpeg1 and
> mpeg2, any sampling rate) and computes the coefficients without
> knowing anything about the samplerate. So the min and max energies
> that can be produced should be about the same, and the ATH is scaled
> so that it's minimum matches the min energy from the MDCT (minus our
> adjustment factor).
>
> Another way to think about this is that the in all cases, the input
> pcm data ranges from -32767..32767, so the dynamic range is always
> the same?
The question is, what kind are the quantizations lame makes at
differend sampling rates?
If ISO/IEC 13818-3 "table B.1 Possible quantization per subband, Layer II" can give a
hint,
the largest value is 16383 = 2^14 -1. A milk maid calculation gives
10*log10(2^(2*14)) = 84.3 db
Whereas the largest value in ISO/IEC 11172-3 "3-B.2 Layer II bit allocation tables"
is 65535 = 2^16-1. Above calculation gives
10*log10(2^(2*16)) = 96.3 db
So can we conclude, that for MPEG2 layer 2 the dynamic range is 12 db lower
than in MPEG1 layer 2, and likewise in layer 3?
>
>
> Mark
>
Robert
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