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In Reply to: Re: It's in the grooves posted by Christine Tham on January 2, 2007 at 17:28:52:
Wait, lets not bring digital compression into the picture, OK that has not much to do with the the dynamics of the signal it has a lot more to do with the amplitude of the high frequency components in the frequency domain of the signal. 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. Even lossy compression will not affect the dynamic range of the signal a great deal it will just limit how fast the signal can reach peak amplitude. Dynamic compression is a purely analog artifact and it affects only the amplitude differences of the signal, it only changes the frequency domain picture as much it reduces the rise time of the signal from volume A to volume B.I hope this did not confuse anybody :-)
Follow Ups:
*** 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).
I was not thinking about pure tones, when i was referring to a ring i was thinking more like ringing of a bell or a triangle real loud, vs playing the lowest registers of an organ (better than a piano or standing base, because of the lower HF content. the bell or triangle will have an almost continuous Fourier transform in the HF region, the low freq pipe organ will have a pretty simple spectrum. Even though the pipe organ will have a larger volume, its digitized waveform will compress much better. If you start playing with synthesized tones, things will become very different.dee
;-D
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