From Sam Costello,
Your Guide to iPod.
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It’s widely said that AAC files – the native format of iTunes and the iTunes Store – sounds better and takes up less space than an MP3 of the same song. Anecdotally, I’ve long believed that this is true, but wanted to put the proposition to a more strict test in order to better help you decide which file format to use for songs in your iTunes library and on your iPod.

So, to conduct this audio file format shoot out, I decided to encode the same song three different ways: as a 128 Kbps AAC file, a 192 Kbps MP3, and as a 320 Kbps MP3 (the higher the Kbps rating, the bigger the file, but the better the quality as well – at least in theory).

Most audiophiles – the people who have great ears and really value the highest possible sound quality – generally detest MP3 and other digital audio formats because they use compression that takes information away from the digital files. While this is true, most average listeners won’t be able to hear the loss in most cases.

The Test Subject
For my test, I chose the song Camellia, by the Philadelphia indie Americana band Buried Beds. This version of the song comes from their EP Po Tolo (a bargain at $6!). Camellia is a delicate song with a number of layered instrumental and vocal sections, as well as a good deal of quiet and subtle parts – something that will hopefully reveal a lot of detail in the various versions of the file.

Though the band makes the song available from their website as a download at 192KB MP3, I used my CD copy (presumably the highest quality) as a baseline.

Here’s what I found:

128K AAC
Encoded as a 128 Kbps AAC file, Camellia sounds great. The strings swell nicely, the keyboard’s notes are sharp and bright, singer Eliza Hardy’s voice is clear and nuanced, her inflections and intake and outtake of breath audible.

File Size: 3.4 MB

192K MP3
As a 192 Kbps MP3 file, Camellia sounds virtually identical to the 128 Kbps AAC version. Though golden-eared listeners may be able to detect a difference, I couldn’t.

File Size: 5 MB

320K MP3
At 320 Kbps, the highest setting for MP3s, there are some very subtle improvements evident. These differences include greater consonance on sounds like “t” and “ch” and greater sibilance on “s”. Still, these are the major changes – the song sounds very similar to the AAC version.

File Size: 8.3 MB

Conclusion
Though there are, no doubt, differences in the sound waves of the three files, they all sound roughly equivalent. Though there is a bit more detail in the 320 Kbps MP3, it’s more than twice as big as the AAC, which is likely not a trade-off worth making.

So, given these test results, I’d recommend sticking with AAC encoding (learn more about file comparisons). If you find different results from your own testing, I’d love to hear from you.