iTunes Question: mp3 to AAC Conversion

[Brize]

Apologies if this has been discussed previously...

I'm pretty settled now with AAC files at 128 kbps in my iTunes library, but started out using mp3, at varying bitrates. I now want to re-encode those mp3 files, but I'm wary of the conversion feature in iTunes. I wouldn't be too concerned going the other way, but given that AAC offers better sound quality at the same bitrate, I'm nervous that the conversion will be constrained by the original mp3 import.

So, does anyone know exactly how the conversion process works? If I were to convert from mp3 to AAC at the same bitrate, will the resulting file resemble a 'true' AAC import, or am I going to have to re-import all of those CDs?

 

[12ibookg4]

if you want the best sound you will need to reimport from the CD's. Going from lossy (mp3) to another lossy (AAC) will give you a much worse sound quality then from the CD to AAC. If you have a lot of mp3's and don't want to import them all it would be better just to leave them as mp3 unless you are really tight on disk space

 

[Brize]

Thanks for the response. So are you saying that converting from mp3 to AAC at the same bitrate would actually reduce the sound quality, or simply that it wouldn't offer any improvement?

 

[12ibookg4]

there definitely would be NO gain. and most likely there would be a loss because the two formats use a different algorithm to determine what part of the sound to throw out and which to keep.

 

[rand()]

Thanks for the response. So are you saying that converting from mp3 to AAC at the same bitrate would actually reduce the sound quality, or simply that it wouldn't offer any improvement?

12ibookg4 is quite correct. It absolutely cannot improve the *true* sound quality. There is simply no way to replace the information lost by the original encoding process.

In theory, upsampling that sound would *approximate* the values for that data. It wouldn't truely replace the data, but, and I stress, *in theory,* you're closer to the original recording. Also, it couldn't replace or even truely approximate the data lost by MP3 encoding, as that data is based on 'what the average listener "can't" hear,' and not simply lost samples.

But I digress. Converting to AAC from MP3 is going to reduce the quality of your sound files, simply because it isn't even upsampling - the sampling rates will be identical, most likely, and the AAC encoding process is likely to lose even more of the remaining original sound - thinking that you "can't" hear the difference.

If the MP3 bitrate is high enough, though - and I'm talking in the 240 to 320 kbps range - you might be pretty darn close, without noticeable artifacts in your AAC. But in all likelyness, the highest you probably encoded those originals was 192; in which case I'd say just grab the CD's and start re-ripping!

Happy listening!
-rand()

 

[Brize]

Thanks guys - I appreciate the responses. I guess it was a stupid question really, but thought it might be worth a shot before re-importing all of these CDs!