::
:: So the highest subbands don't have any scalefactor? I know that
:: Brandebourg said that there is no proof that >16kHz really contribute to
:: the hearing of the music, and then it could be intentionnal, but could
:: it be a "bug" or mistake in the mp3 specs?
::
40 Hz...16 kHz (+0.2dB,-0.3dB)°) seems to be not enough to pass AB tests.
25 Hz...18 kHz seems to be sufficient, and 20...20 kHz are recommended.
These are values for monoton decreasing frequency response. Using a slight
emphasis from fu-1.5 kHz to fu reduces significantly the bandwidth needs.
The easiest way is to do this with a static frequency response like:
12.5 kHz 0.0 dB
13 kHz -0.2 dB
13.5 kHz 0.0 dB
14 kHz +0.2 dB
14.5 kHz +0.4 dB
15 kHz +0.6 dB
15.5 kHz +0.8 dB
16 kHz +1.0 dB
16.5 kHz -oo dB
The frequency response should be so calculated, that the white noise'
cochlea excitement is not changed. This should be possible for fu >= 14 kHz.
Better methods are calculating this preemphasis dynamically from the actual
signal.
I've tested the first method with fs=29.4 kHz and got a nearly
indistinguishable signal compared to the classical low pass filtering with
fu = 0.45*fs = 13.2 kHz resulting in "poor" quality.
To my mind 16 kHz are enough for music. Using some emphasis tricks makes
this statement more secure.
Have someone a piece of music with a triangle? For my experiments I still
need some very tonal high frequency samples.
:: After all, I think that in 48kHz encoding some freq higher than 16kHz got a
:: scalefactor, so it could be theorically be possible to affect a scalefactor.
::
No. The scaleband assignments are different for 32/44.1/48 kHz, so you got
16 kHz for all fs.
Long Blocks Short Blocks
32 kHz: ...15.25 kHz ...14.92 kHz
44.1 kHz: ...15.96 kHz ...15.50 kHz
48 kHz: ...15.96 kHz ...15.62 kHz
--
Mit freundlichen Grüßen
Frank Klemm
PS: °) minimum requirements of studio equipment frequency response.
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