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Why are 128kbit/s MP3s usually 44,100 Hz?
eamon123
post Oct 14 2012, 01:44
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Since 128kbit/s MP3s usually has a low-pass filter at 16,000 Hz, and the Nyquist-Shannon theorem states that all frequencies under f/2 Hz can be totally described at an f Hz sampling rate, why not encode at 32,000 Hz? Wouldn't it save more space?
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saratoga
post Oct 14 2012, 04:03
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QUOTE (eamon123 @ Oct 13 2012, 20:44) *
Since 128kbit/s MP3s usually has a low-pass filter at 16,000 Hz, and the Nyquist-Shannon theorem states that all frequencies under f/2 Hz can be totally described at an f Hz sampling rate, why not encode at 32,000 Hz? Wouldn't it save more space?


Since encoding happens in the frequency domain anyway, there isn't much savings. It'll just not encode those frequencies, which is pretty close to downsampling, but much easier to implement.

That said, at very low bitrates LAME does downsample.
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eamon123
post Oct 15 2012, 05:02
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QUOTE (saratoga @ Oct 14 2012, 04:03) *
Since encoding happens in the frequency domain anyway, there isn't much savings.


Listen to these test files and tell me what you think (24 vs 48 kHz, both with 11.5 kHz lpf):


https://rapidshare.com/files/666351554/Baba...y24.11.5lpf.mp3
https://rapidshare.com/files/2623776446/Bab...y48.11.5lpf.mp3

QUOTE (halb27)
pre-echo issues get worse


If you ask me the attack sounds as good in the 24 kHz file as the 48 kHz, and everything else sounds better. What do you make of it?


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