[Thumannator]

Searched on this, but didn't see anything, so here goes...

To date, I have not done much in the way of converting my old MP3s to AAC files, mostly because I have not yet felt like going through all of my CD collection again. However, my "old" 2G 10GB iPod is beginning to get a bit crowded. It was my understanding that AAC encoded at the same bit-rate is supposed to provide superior quality sound, but with a reduced file size (which would be good for said crowed iPod). So, the other day, I popped in a CD to re-encode it to AAC and see how much space was truly saved. To my surprise, the resulting files were on average 0.1 MB larger!

So my question to all is, what did I misunderstand about the different file formats and/or what might I have set wrong in my iTunes settings that is making my AAC files too large?

Thanks.

[Jacke]

Yes, AAC provides better quality at the same bitrate, but thinking a file encoded with AAC at 128 kbps (kilobit per second) would be smaller than an MP3 encoded at 128 kbps (kilobit per second) is, well, wrong.

128 kbps, meaning the data will take up about 15 kilobyte per second, will be as large as as the same clip encoded with any other encoder set at that datarate. So AAC might give similar quality at 112 kbps or even 96 kbps as MP3 at 128 kbps, but also giving smaller files.

[memento]

Right. The advantage of AAC is better quality, so you can use a lower bitrate to get the same quality as MP3.

[voodoo]

I thought AAC was aways VBR. That could make them slightly smaller than mp3. If they're not well they're not.

[Millennium]

This is the biggest thing that people don't understand about audio and video: bitrate does not equal quality. Bitrate determines only one thing: how big the file is. If you recorde them all from the same source, a 128K MP3, a 128K AAC, a 128K WMA, and a 128K uncompressed AIFF will be almost the same size, and the audio streams in this file will be exactly the same size. Header information and metadata can make filesizes slightly larger for some formats than others, but generally no more than a few kilobytes.

What makes AAC a better codec than MP3 is that it sounds better at lower bitrates. If you can make a 128K AAC that sounds as good as a 192K MP3, you've saved a lot of space. That's why people say that AAC files are smaller; they sound just as good at lower bitrates.

[memento]

For my mp3 collection, I used to rip at 160 mp3 or 192, but then when AAC was supported by my iPod, I re-ripped at 128 AAC, and the files sounded MUCH better still. I even had a few CDs that I originally ripped in AIFF just to maintain the sound quality, I re-ripped those at like 192 AAC and they still sound great.