Convert MP3 to AAC - an okay idea or no?

[nonoitall]

I have a rather large collection of MP3s (who doesn't) and most are in the 128-192kbps range. I'm looking to get them a little bit smaller and am wondering what the best options are as far as a destination format. For example, OGG and AAC both sound adequate at ~64kbps to me. But, I know that transcoding from MP3 to OGG isn't an optimal operation, as the MP3 encoder may have thrown away things at 128kbps that the Vorbis encoder would've kept at 64kbps. Is the story the same for MP3-->AAC conversion?

I know I'm not going to gain any quality by transcoding, but I'm just trying to get a file as close to what would be produced from a lossless source as possible. I'll retain the original MP3s in an archive, but I just want something more compact for casual listening.

[kumi]

That's odd. You want to get them smaller, but you also want to be "close to lossless"? Recompressing them to AAC, Vorbis, or any other lossy format will entail a loss of quality, no matter what your target bitrate.

Try it and see: take a 192kbps MP3 you know by heart, and encode it to 128kbps AAC. Can you tell the difference?

[nonoitall]

No, I don't want a result close to lossless - I want a result close to what would be produced from a lossless source. If I encode a FLAC file to OGG Vorbis at 64kbps, it will be a better result than if I had encoded the FLAC to MP3 at 128kbps, and then used the MP3 to create a 64kbps OGG. The reason being that the MP3 encoder threw away information that the OGG encoder would've kept, had the source been lossless. Is the situation the same with AAC?

[kumi]

Of course. AAC and Vorbis are both lossy, and you already threw out information in the original encoding to MP3. It might sound a little better than Vorbis, or a little worse, but it will be a LOT worse than skipping the intermediate MP3 step.

(Quantitatively... you'll have to listen with your own ears to see if it makes a qualitative difference.)

[nonoitall]

Okay, thanks. It's just that I read tons about how MP3->OGG is bad bad bad, but I hadn't seen anything saying the same about MP3->AAC. I thought maybe AAC was modeled closer to MP3 or something, but I guess not. Thanks again.

[Dark Shikari]

MP3 -> AAC is fine. 64kbps HE-AAC sounds basically equivalent to MP3 of any bitrate unless you're on very good speakers/headphones and are looking for the difference.

96kbps AAC-LC is roughly as good as 128kbps MP3, to my ears.

[cogman]

even going from MP3-MP3 (for whatever reason) is a bad Idea. Every time you encode a file (even at the same bitrate) with a lossy encoder, you loose data. If you can avoid it at all, then do. But you should definitely check it out and see what you think. Often times you get Audiophiles that swear they can hear even very minuet differences in sounds that will curse you too your grave if you don't use anything above 300 kb/s from the original source.

Just remember, this is for you, and since what something sounds like is very subjective, you will just have to decide if it is good enough. So go ahead and do it (heck do an ogg conversion as well) and see what you think. If you like it, keep it, if not, then don't :). Hope this helps.