I'm planning on to convert big fat mp3 flies (196kbps or more) to smaller AAC (128 kbps VBR).

Does anyone knows the method that iTunes uses?

Is it a direct transcodig from mp3 to AAC?

or it more like: mp3 to PCM to AAC?

Thanks

When you convert to another format, it will do so directly (not that it makes any difference).

Remember that the quality of your 128kbps files will be piss poor

Does it matter? The only way that these two methods are meaningfully different is very slight amount of rounding error, which I think is not meaningful relative to the audio compression that's going on.

I'd recommend that you keep the original high-quality mp3 files around - I assume that you're just transcoding so you can fit more music on your portable. But as you've probably heard before, transcoded files aren't good for quality...

Internally it's probably doing MP3 to Floating Point to AAC. If it's smart about it, anyway.

Thanks for your help!

Yes, the reason for me to transcode is that files @ 196 Kbps or higher aren't "that" portable, and this becomes a big issue when using flash memory audio players.

Although a reduction in bitrate is often perceived to be a reduction in quality of reproduction, the fact is that since you are obviously listening on a portable with headphones your best bet is to try to construct a reasonable facsimile of recorded music you may be familiar with while listening to a decent room based stereo system and (ugh) your favorite recording.
Bitrate notwhithstanding, some form of DSP enhancement is necessary with headphone listening in order to realize reasonably accurate sound.

Transcoding with a program such as foobar or winamp with third party dsp enhancements such as crossfeed, EQ, noise sharpening and such will reduce the effects that all of us dread while listening to sound in a near field environment namely, spatial distortion-which accounts for and can be eliminated almost entirely by the above methods. Spatial distortion accounts for most all of the variations in reproduction of various compression methods (above 128kps) used these days.

99% of everything you buy these days is garbage. Until you make it the way you want it.

flames encouraged.