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Rip losslessly to flac with abcde
Authored by: BadgerUMD on Oct 21, '05 11:05:30AM

Not really true -- a true square wave has infinite frequencies (or at least higher than the sampling rate and your range of hearing), which any encoder (even "lossless" WAV) will alias to lower frequencies that you "can" hear. So if one encoder suppresses these alias frequencies better it doesn't make it more "lossless" -- you've simply passed data to the encoder that the writes didn't expect -- non-audio data.



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Rip losslessly to flac with abcde
Authored by: shoelzer on Oct 21, '05 11:15:27AM

Yes, it really is true. I'm talking about the codec being lossless. If the audio samples coming out match the audio samples that went in, it's lossless. You're talking about the sampling process being lossy, which of course is true, but it's a totally different issue.



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Rip losslessly to flac with abcde
Authored by: kd4ttc on Oct 21, '05 03:11:31PM

The thing the codec is trying to be smart about is to work with audio that really will come along. If the inventors of a codec realize through analysis of real audio that certain frequencies never come up in real life, then develop a codec that takes advantage of that truth of nature they may have an insight that allows a significant advance in technology. So if it is lossless with real audio but loses certain frequency components in fantasy signals I would still call it lossless.

Just because an arbitrary waveform has a certain frequency in the range of 50 Hz to 20 kHz does not make it a valid audio input. True square waves of pressure in air cannot be generated by any known phyisical method. No moving body can instantaneously move. Even electronic circuits that generate square waves are limited by rise times and may exhibit slight ringing.

As far as square waves and audio circuits, a crude test of audio gear is to run a square wave through and see what comes out. However, the purpose of this is not to look for whether the process drops a bit. One scopes the output looking for rolloff, ringing, and high and low frequency losses.

For audio testing that would be relevant consider something like the test disk at http://www.interstudio.co.uk/sndchk.htm That will privide not only audio that is well selected for testing sound reproduction equipment, but would be a suite that others could use in independent verification of the system.

Running a square waveform into a codec may be an easy test, but the ease with which it is done misses the point of why the testing is done in the first place.

---
Stephen Holland, M.D.



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Rip losslessly to flac with abcde
Authored by: DylanMuir on Oct 25, '05 01:49:03AM
"Lossless compression" means no information is thrown away.

MP3 and FLAC are analogous to JPEG and GIF, or ZIP. JPEG and MP3 throw away information that is considered unimportant, or below our threshold of detection. FLAC, GIF and ZIP should take some binary stream and compress it in a way that that stream can be recovered PERFECTLY.

Arguing about square waves misses the point -- FLAC can encode any valid PCM stream and reproduce it bit for bit on decompression. The sampling process that makes a true square wave impossible is not the issue here.

D.

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