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In Reply to: Ugh, ugh.... posted by Penguin on January 2, 2007 at 18:12:06:
*** A very dynamic low frequency signal will digitally compress a lot better than a loud but steady high frequency ring, and the loss less compression will affect the amplitude and the dynamic range of the signal exactly 0 db. ***This is not true, and you can check this out yourself by observing the compression ratios of various codecs depending on the source signal.
Steady state sine waves compress very well, regardless of amplitude or frequency. More so than a "very dynamic low frequency signal." If you don't believe me you can test it out yourself. Synthesize two signals: one a constant sine wave at 15kHz 0dB amplitude, and the other a low 50 Hz signal that varies in amplitude from -96dB to 0dB (you can modulate this using a sine or triangle wave).
The first signal will losslessly compress better than the second signal. At least on a codec that compresses based on a Fourier transform. Even WinZip will compress the first signal better than the second, and WinZip is notoriously poor at compressing audio.
I didn't bring digital compression into the picture, Robert did (in his reference to the Mahler recording). But you are right that lossless bitstream compression is not the same thing as dynamic compression. But I don't think that Robert was necessarily confusing the two either, he was simply citing two unrelated things that affect the maximum amount of recording time (groove spacing on LP, vs lossless compression ratio on SACD).
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Follow Ups
- Actually it's a lot more confusing than that ... - Christine Tham 18:26:49 01/02/07 (2)
- I just want to make sure we do not mix up the two types of compressions... - Penguin 20:41:56 01/02/07 (1)
- Well, I don't think anyone was "mixing it up" but thanks for the concern (nt) - Christine Tham 22:21:23 01/02/07 (0)
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