I'm in the process of reripping all my albums from 192 kps CBR MP3s to EAC/Lame Alt Preset Standard MP3s, and while watching the little dos Lame window do its thing, I started wondering what exactly determines what bit rate is used for each portion of the song.

Is it amplitude, or musical complexity, or something else? I haven't been able to deduce anything from the albums I've ripped so far...

Anybody know?

As I understand it, the bit rate used to encode a specific passage is primarily a function of the musical complexity of that passage.

More specifically, the psycho-acoustic analyzer determines how much of the information in each passage it can throw away while maintaining the best sound quality possible, given the overall level of compression being targeted. A complex passage requires more bits to represent than silence does, to use an extreme example.

I don't know for sure, but I doubt that amplitude has anything to do with it. Frequency might, since I think it takes more bits to accurately represent higher frequencies. But I'm guessing at this point.

It's mainly frequency and stereo separation that determine the complexity of a passage.

This makes sense, thank you both. One more little mystery solved.

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Uh, I hope you mean you're re-ripping from your original source material, and not just re-encoding, right? It sounds like it, but some people don't know. MP3 is lossy, and once it's gone, it's gone. Re-encoding at a higher bitrate does nothing. But hopefully you know that already

Yeah, methinks VBR looks at the frequencies, as well as the complexity of the passage. I know in some --aps versions of Apocalyptica songs (awesome group, for those of you who don't know about them. Finnish cello quartet that plays Metallica) are very interesting to watch the bitrate jump. In quiet single-cello solos, it's fairly far down, then when they all jump in and start doing different stuff, it just spikes.

(-:Stephonovich

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Yes, I'm reripping from my CD collection. I originally ripped my collection using Musicmatch into 192 CBR MP3s when I first got my iPod. Since then I've discovered the wonders of EAC/LAME, but was too lazy to redo everything until now. (500 albums/30 gigs is not a small project.) I'm using the release of iTunes for windows as an excuse to start over. So I'll be seeing a lot of that anachronistic DOS window over the next month...

I dunno if you're interested, but one method is to rip everything to FLAC. This is a lossless codec, and is free. Usually you can to 3/4-1/2 the size of an uncompressed WAV. Best of all, it offers tagging, gapless playback, and all the fun stuff. You need some serious HD space, of course, but this way, any time a new codec comes out, or you want to try something different, you can just re-encode from the FLAC files, thereby skipping the lengthy re-ripping process.

(-:Stephonovich

Unfortunately, I'm working with a 20 GB laptop, so storage space is at a premium (you know something's wrong when your ipod HD is bigger than your main computer HD). However, I think I'll be happy with the quality of the APS MP3s for a while, so I'm backing them up on CD-Rs as I go along. I would hate to lose all that work just because my iPod crapped out for some reason

All the same, re-ripping has a nice ritualistic quality about it. I'm forced to go back and listen to my entire collection again, and I often re-discover gems I had forgotten about...

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I'm about to re-rip my collection, I didnt know FLAC was supported on the ipod. I thought just WAV,MP3, and AAC were supported.

Can you comfirm that FLAC works on the iPod? I just want to make sure before I start using it.

This would be great, I'm tired of the gaps between songs on live albums.

Thanks, Markkr

No, FLAC doesn't work on the iPod. I was just saying he could store them on his HD, and then re-encode lossy files from those. I plan on doing that, once I acquire a 120GB HD. (soon, very soon)

AFAIK, the only DAP's that support FLAC are the Neuros, (which doesn't have FLAC support yet, only Ogg Vorbis. At least last I looked) and the Karma. The other Rio players might too, I'm not sure.

(-:Stephonovich

Thanks for confirming that.