ext_29615 ([identity profile] bovil.livejournal.com) wrote in [personal profile] mishalak 2007-04-06 05:55 am (UTC)

iTunes can do VBR, it's just a matter of settings. The rewards aren't just from VBR, it's a combination of things.

EAC has some really sophisticated error-checking functions that deal well with some of the "slack" in the audio CD specification. A perfectly mastered audio CD ripped on a perfect burner will always produce a stack of .wav files that's identical to the last rip, but we know how well "perfect" and "technology" go together. Factors including "gapless" CDs, mastering errors, dirty discs and player errors can all contribute to subtle (and in some cases, unsubtle) problems.

Once the .wav data is ripped, it needs to be compressed.

Now VBR is nice; it sets a "floor" bit rate for the least-complex groups of data frames, but increases the bit rate to provide more fidelity in complex frame groups. More detail where needed, less total storage than constant bit rate. This is a big deal in classical music (with its wide frequency range), but isn't inconsequential with any music.

Where LAME wins out is in its multi-pass compression process. It's more discriminating about what audio data is discarded during compression, providing a more "true" representation than other codecs at the same bit rate. It does a better job of adjusting the variable bit rate on the fly, again providing a more "true" representation in a smaller file.

That's not to say that other MP3 codecs couldn't do the same thing, it's just that many commercial developers choose to be a bit more sloppy.

According to the graphs, AAC is more efficient and precise overall. MP3 is universal, though, and newer MP3 codecs are approaching AAC in quality/compression.

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