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Some inconvenient facts

"If they took the time to take an MD5 sum on the original file and a compressed->uncompressed version they would have found the results to be identical."

Unfortunately there are some inconvenient facts that may confuse things. I will describe a little experiment I did tonight. (I've done this before, but I wanted to do it again to make sure I got all the details exactly right before posting.)

1. I started with a 96/24 WAV file that I had previously made using Soundforge 10c. This file was pure, i.e. it was made from a digitization of an analog waveform played on a tape recorder. The recording had never been "polluted" by being passed through any evil "lossless" compression. Call this wav file FILE 1.
2. I took FILE 1 and used dBpoweramp and compressed this using FLAC level 8. Call this FLAC file FILE 2.
3. I took FILE 2 and used dBpoweramp and converted this file back to WAV. Call this wav file FILE 3.
4. I took FILE 3 and used dBpoweramp and compressed this using FLAC level 8. Call this FLAC file FILE 4.
5. I took FILE 4 and used dBpoweramp and converted this file back to WAV, Call this WAV file FILE 5.

Here is what I observed. Files 1, 3, and 5 were all WAV files of identical length. Files 3 and 5 had identical MD5 checksums. File 1 had a different MD5 checksum. However, by differencing the audio samples in Files 1 and 3 I verified that the audio samples in files 1 and 3 were identical, i.e. the files differed only because of the headers. It looks like dBpoweramp likes to write headers one way and Soundforge a different way. What this shows is that different programs can produce different WAV files that contain identical audio samples. This is not about FLAC compression, it's about any audio software and also about the WAV format that allows the same audio samples to be expressed in different ways.

If a difference in WAV file headers affects sound then it is because of poorly designed player software. For example, memory playback software would load an entire file into RAM memory. Files 1 and 3 would load identical contents into RAM memory. At that point the playback software will then be running on identical data in identical memory locations and the result is going to be the same. If non-memory playback software is used then while the music is playing the software will be occasionally operating on different headers and the audio data may be in different memory locations, and this may affect cache hit ratios and other aspects of program execution that might make the sound different (possibly better or worse according to some individual's taste).

If there is BS here, it's on the part of people who don't know enough about computers to understand how they actually work. I didn't read the article, so I have no comment on whether this statement applies to the author. Of course, if the computer had been connected to a DAC that was properly designed then the poorly designed player software wouldn't matter either, since the DAC would produce the same output regardless of the quirks of player software. As the quirks of player software and DAC sensitivity will continue to exist with or without FLAC compression this brouhaha has nothing to do with FLAC and all about crummy player software or DAC hardware.

As someone who makes recordings, I would find it completely unacceptable if two WAV files containing the same samples sounded differently. I am deliberately changing the samples in the file to make a recording sound the way I want, and it would be completely unacceptable if the recording were changing for other reasons. Were I to hear these differences with my software, I and every other more or less competent recording engineer would get to the bottom of things, and/or junk the gear and start over. Life is too short to put up with this BS. This is why many audio engineers use the name "audiophool" to describe audiophiles who bumble about without a clue as to what they are doing and then reach totally unfounded conclusions.

Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar


Edits: 01/05/12
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