MP3 Encoding and Quality

Bob Katz Leave a Comment

Name: Dan Humann
Message: Hi Bob: Hopefully this will get to you! I purchased your i tunes music book and just finished reading it. Truly an awakening. The question is, can you encode to a 320 kbps MP3 from a 24 bit 48 or 96k stereo file or does the file have to be 16 bit 44k first?

I thought I made it clear in the book that you can and SHOULD encode to an mp3 from a higher wordlength source. Over here any encoder I have will accept 32 bit float, but Apple seems to have an in-house restriction requiring 24 bit files. As for the sample rate conversion, it depends on the exact architecture of the software. If you have software which takes in the high sample rate source, downsamples it and outputs it as 3244 float, and then inputs it to the codec, then you can

and should do it like that. But it probably has to be two steps. There is no codec per se that I know of that takes in 96k and will make a 44.1 mp3 or AAC. However, Apple’s MFIT suite of tools can do that, all at once, but it is done in two steps. And if you know the terminal codes you can even make it output mp3 instead of AAC!

It is not necessary to be 1644 first, and in fact, it should be 3244 or at least 2444 for the best results when converting to mp3 or any coded format. Again, I thought I had made this clear in the book.

The next question do you believe a 320 kbps CBR file sounds better than the ACC 256kbps VBR?

I think yes, if both codec are AAC. If one is mp3 and the other is AAC it’s a subjective choice between two algorithms and who’s to say? I would bet on the 320 k CBR mp3, personally, as sounding a little better than the 256 vbr AAC, but I haven’t done the absolute shootout.

I’m not concerned with the file size difference between the two. It just seems like a lot of bother to play around with the whole ACC format when you can just encode for the highest quality MP3 and get on with ones life.

Well, if you are dealing with Apple and iTunes might as well make AAC. If your mp3 clients can take the 320k then there’s absolutely nothing wrong with that either. It’s the wild wild west, you have to know what phone they are playing on….   mp3 is of course playable by everything.  But I play in the iTunes world, and many clients have iphones, so AAC is my preferred choice. I have to make files that they can audition if they are eventually going to iTunes.

Hope this helps


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