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Topic: Apple Lossless "DIFF" tests (Read 3034 times) previous topic - next topic
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Apple Lossless "DIFF" tests

Reading this forum gave me the idea of doing some tests on Apple Lossless encoded files to see exactly how lossless they really are. One user reported using the UNIX command "diff" on an original WAV file and a WAV file converted from an ALAC file converted from the original WAV file. His results were identical. I decided to repeat the procedure, but testing AIFF files as well.

The results were quite interesting.

While the original WAV and the 3rd generation WAV reported identical, the original AIFF and 3rd generation AIFF files did not. In fact, file sizes differed by 6 bytes, the alac2aiff file being larger. I've also tested iTunes converting WAV to AIFF and then back to WAV, and vice versa. Those proved to be identical.

Any ideas explaining the behavior? Thanks.

Tests were done in the latest iTunes on a Mac platform. iTunes version 7.0.2

Code: [Select]
diff cdda2wav.wav alac2wav.wav -s
Files cdda2wav.wav and alac2wav.wav are identical

diff cdda2aiff.aif alac2aif.aif -s
Binary files clean.aif and radio.aif differ
 

Apple Lossless "DIFF" tests

Reply #1 –
WAV and AIFF files have headers and other metadata that can differ even if the actual sound signal doesn't, so always export the raw signal before doing such a comparison (you can use pretty much any audio editor for this, if you haven't got one yet Audacity can probably do this, although I haven't checked).