AAC vs. MP3: An ITunes Sound Quality Test

Which Encoding Is Best for the Average Listener?

iTunes sound check
Screen Capture by S. Shapoff

Most audiophiles—the people who have superior hearing and place great value on the highest possible sound quality—usually detest MP3 and other digital audio formats because the formats use compression that removes information from the digital files to save space. It is true that these formats delete information, but most average listeners can't hear the loss. As an average listener and consumer of music, I conducted a test to determine if one format out-performed the other in sound quality.

 

It’s widely believed that AAC files—the preferred music format of iTunes and the iTunes Store—sounds better and takes up less space than an MP3 of the same song. I put the theory to an exacting test to help you decide which file format to use for songs in your iTunes library and on your iPhone and iPod.

To conduct this audio file format shoot-out, I encoded two songs in different ways: as 128 Kbps AAC and MP3 files, as 192 Kbps AAC and MP3 files, and as 256 Kbps AAC and MP3 files. The higher the Kbps number, the bigger the file, but the better the quality—at least in theory. For all files, I used the encoder built into iTunes.

The Test Subjects

For my test, I chose two songs: the quiet, intricate "Wild Sage," by The Mountain Goats, and the loud, raucous cover of "Leaving on a Jet Plane," by Me First and the Gimme Gimmes.

"Wild Sage" is full of subtle pianos and finger-picked/strummed guitar, with high, breathy singing.

I chose it because I'm hoping that those intricate sections will reveal a lot of detail in the various versions of the file.

"Leaving on a Jet Plane," on the other hand, is fast, loud, bass heavy, and full of complex drum sections. This song will hopefully show more dynamic range and reveal other things that the quieter "Wild Sage" won't.

I used my CD copy of both songs—presumably the highest quality available to me—as a baseline.

Here’s what I found:

256 Kbps

  • Wild Sage: Both versions of the song sound great at 256 Kbps. I can clearly hear the plucking of the guitar strings and the breathiness of the vocal with no distortions anywhere. The MP3 and AAC versions sound nearly identical. No clear winner here. The MP3 version is 1.2MB smaller, though.
  • Leaving on a Jet Plane: Same situation here. The song sounds great. The vocal is clear with subtle intonations and a general sense of brightness, but neither sounds appreciably different.

192 Kbps

  • Wild Sage: This version sounds a bit muddied compared to the 256 Kbps version. However, there's still no clear distinction between AAC and MP3. The MP3 is almost 1MB smaller.
  • Leaving on a Jet Plane: The pattern holds true. Not as good as 256 Kbps but similar between the two file formats.

128 Kbps

  • Wild Sage: Finally a difference. In this version, the AAC version is a bit clearer and brighter than the MP3, which suffers from slight muddiness and a slurring together of some sounds. The file sizes are almost exactly the same, making the AAC version the clear winner here.
  • Leaving on a Jet Plane: Here the AAC is slightly superior in drum clarity. Otherwise, the songs sound fairly similar and are exactly the same size.

    Conclusion

    Though there are, no doubt, differences in the sound waves of the three files, they sound roughly equivalent. Though there may be a bit more detail in the 256 Kbps MP3, it's difficult for an untrained ear to discern, and the files are much larger than either other version. The only place you're likely to hear a difference is in the low-end 128 Kbps encodings, but I don't recommend those anyway.

    So, given these test results, it seems that the debate between AAC and MP3 may come down to a matter of taste, opinion or having better ears than I have.

    File Size by Encoding Type/Rate

     MP3 - 256KAAC - 256KMP3 - 192KAAC - 192KMP3 - 128KAAC - 128K
    Wild Sage7.8MB9.0MB5.8MB6.7MB3.9MB4.0MB
    Leaving on a Jet Plane4.7MB5.1MB3.5MB3.8MB2.4MB2.4MB