Hello Mark,
Tuesday, May 23, 2000, 8:14:18 PM, you wrote:
MT> Actually, there really are 22 "critical bands" or "scale factor bands"
MT> used by MP3. I guess we should stick to the C convention, and call the
MT> last band the 21'st band. Here are the frequency ranges,
MT> along with the ATH:
MT> sfb= 0 freq(khz): 0.00 .. 0.15 ATH=-93.46
MT> sfb= 1 freq(khz): 0.15 .. 0.31 ATH=-103.59
MT> sfb= 2 freq(khz): 0.31 .. 0.46 ATH=-106.77
MT> sfb= 3 freq(khz): 0.46 .. 0.61 ATH=-108.40
MT> sfb= 4 freq(khz): 0.61 .. 0.77 ATH=-109.43
MT> sfb= 5 freq(khz): 0.77 .. 0.92 ATH=-110.16
MT> sfb= 6 freq(khz): 0.92 .. 1.15 ATH=-111.02
MT> sfb= 7 freq(khz): 1.15 .. 1.38 ATH=-111.76
MT> sfb= 8 freq(khz): 1.38 .. 1.68 ATH=-112.81
MT> sfb= 9 freq(khz): 1.68 .. 1.99 ATH=-114.04
MT> sfb=10 freq(khz): 1.99 .. 2.37 ATH=-115.84
MT> sfb=11 freq(khz): 2.37 .. 2.83 ATH=-117.92
MT> sfb=12 freq(khz): 2.83 .. 3.45 ATH=-118.98
MT> sfb=13 freq(khz): 3.45 .. 4.21 ATH=-118.92
MT> sfb=14 freq(khz): 4.21 .. 5.13 ATH=-116.48
MT> sfb=15 freq(khz): 5.13 .. 6.20 ATH=-113.20
MT> sfb=16 freq(khz): 6.20 .. 7.50 ATH=-111.72
MT> sfb=17 freq(khz): 7.50 .. 9.11 ATH=-110.10
MT> sfb=18 freq(khz): 9.11 ..11.03 ATH=-106.49
MT> sfb=19 freq(khz): 11.03 ..13.09 ATH=-98.69
MT> sfb=20 freq(khz): 13.09 ..16.00 ATH=-84.16
MT> sfb=21 freq(khz): 16.00 ..22.05 ATH=-48.04
aha... I thought the downside of mp3 was that the heritage of L1 and L2
was that there was a linear distribution in freq ranges, but this
doen't look linear to me ... So instead of 32 linear just 22 log.
thanks, I'll do some reading-up...
MT> The ATH is given in db, normalized so that the loudest possible 3khz
MT> sine wave is about 1db. (normalization is a little different than the
MT> db used in your plot) The value of the ATH in band 21 means that
MT> humans cannot hear a 16khz signal which is weaker than -48db.
sounds plausible, because I did some highpass filter hearing tests on
my music ("can I hear artifacts, or is it just imagination"), and
roughly perceived I could hear -40dB...
MT> ...
MT> inaudible. So the claim is that original + inaudible_error
MT> sounds the same as the original.
MT> ...
I'll have to think about what you said concerning the error etc...
thanks for the lengthy explanation.
My idea was just: does it have to be bad that the _average_ volume of
the error is -44dB? If I display the freq analysis real-time the graph
ends up much higher most of the time, and also lower at other times.
I thought that at the times where (in time) the original ended up
below that -48dB treshold, the encoder made a quantized version that
is even lower, but inaudible (so bigger error, but no audible parts).
Then later when you sum the whole song, the average error gets bigger
than the -44dB, but not on the important parts?
I'll try to gain some more insight...
thanks
--
Best regards,
Roel mailto:[EMAIL PROTECTED]
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