Music Spotlight Special Series: Amazon vs. Apple, Music File Functionality

October 11, 2012
By

KF on KND’s series comparing Amazon to Apple for digital music continues today with a look at music file functionality between the two vendors. Here’s a rundown of posts in the series so far:

Music Spotlight: Amazon vs. Apple – Introduction
iTunes vs. Amazon MP3 Store
Amazon vs. Apple, Digital Music Library Management

MP3 vs. AAC

The reason why music file functionality is being addressed here is that Amazon sells its digital music in MP3 format, and Apple sells its digital music in AAC format (also known as .M4a).

Device Compatibility

Any recently-manufactured (within the past two years or so) device capable of playing digital audio files should be able to play both MP3 and AAC format files. Older, non-Apple devices will play MP3s, but may not play AAC files.

Tomorrow’s post in this series will get into more detail regarding audio player functionality on various devices that are compatible with iTunes and Amazon’s Cloud Player.

DRM

Apple began phasing out its DRM in 2009, and DRM is no longer present on any music you buy from iTunes.

Amazon’s MP3s have never had DRM to begin with.

File Format Differences

MP3 is generally considered the most “open” digital music file format. This means that it’s most likely to be compatible with any device or software program that can play digital audio.

AAC is a more recently-developed digital music file format, but it was not invented by Apple. AAC uses a different, newer type of file compression than MP3, and as a result it’s reported that AAC files are a little (in terms of file size) than the same music in MP3 format and also have slightly higher sound quality.


Lossy vs. Lossless Audio File Compression

The DigitalTips website provides this information about digital audio file formats:

—————————————

Like any other kind of file on your computer, an audio file is simply a container for data. To fill that container, a codec may be used to encode the data for storage and decode it for playback.
To make the most of limited storage space, the codec may eliminate some data. This “paring down” is what allows thousands of songs to be stored in a portable music player. Some codecs use psychoacoustic principles to determine which data can be discarded with the least impact on sound quality.

Codecs that reduce file size by eliminating data are known as lossy. Here are some examples of lossy codecs:

  • MP3
  • MP3 VBR
  • MP3 Pro
  • AAC
  • WMA
  • More


Codecs that reduce file size while precisely reconstructing the original signal are known as lossless. Here are some examples of lossless codecs:

  • FLAC
  • OGG
  • WMA Lossless
  • More

File Formats and File Sizes

Lossy codecs operate at differing data rates, also known as sampling rates or bit rates. Encoding more bits allows higher audio quality, while encoding fewer bits allows greater efficiency. So an MP3 encoded at 320 kilobits per second (kbps) will sound far better than one encoded at 128kbps—but it will also take up more storage space.

——————————————-

You’ll notice that MP3 and AAC are both on the “lossy” list, so the real question here is the bitrate at which each vendor encodes its files. Apple has this to say about its AAC files:

Purchased songs are encoded using MPEG-4 Advanced Audio Coding (AAC) format, a high-quality format that rivals CD quality. Songs purchased and downloaded from the iTunes Store are AAC Protected files and have a bitrate of 128 kilobits per second (kbit/s). The purchased song should sound as good as or better than a 160 kbit/s MP3 file. Because the bit rate is lower, though, the AAC file takes less disk space than the MP3 file.

Amazon reports this about its MP3 files:

Bit Rate: Where possible, we encode our MP3 files using variable bit rates for optimal audio quality and file sizes, aiming at an average of 256 kilobits per second (kbps). Using a variable bit rate allows us to allocate a higher bit rate to the more complex sections of music files while using a smaller bit rate for the less complex sections. The average of these rates is then calculated to produce an average bit rate for the entire file that represents the overall sound quality. Some of our content is encoded using a constant bit rate of 256 kbps. This content will have the same excellent audio quality at a slightly larger file size.

So in terms of quality, Amazon’s MP3s should have a slight edge over Apple’s AAC files. However, if this is so it would be such a slight improvement that the average listener wouldn’t be able to tell the difference. Only those with the most sensitive ear and top-of-the-line audio playback equipment (like that offered by Sonos or Bose) would have much of a shot at enjoying the very slight improvement in sound quality.

File Size and Sound Quality

According to my research and the iTunes, Amazon and DigitalTips information excerpted above, iTunes AAC files should be smaller than the same audio file provided by Amazon in MP3 format. However, in spot-checking my own library, I’ve found this is not case. I was able to compare numerous files I bought from Amazon in MP3 format, then imported to iTunes, which converted them to AAC format when it added them to my iTunes library. I also looked at some of the digital music files I originally purchased from iTunes in AAC format, to make sure the MP3 source files from Amazon weren’t introducing other variables that could affect file size during file conversion by iTunes.

I noticed when checking the “Info” for each song in iTunes, they were all encoded at the higher quality 256 kbit/s bitrate, not the 128 kbit/s bitrate Apple mentions in its description of iTunes AAC files. The higher the bitrate, the larger the file, so it’s not surprising that I found none of my AAC files were smaller than the same file in MP3 format. Actually, in every comparison I did, the AAC files were slightly larger. For example, 4.34MB in MP3 format versus 4.5MB in AAC.

As with the sound quality difference, this file size difference is negligible.

Conclusion: Six of One, Half Dozen of the Other

After doing my own, real-life tests and comparisons, I’ve concluded there’s no particular advantage to either the MP3 or AAC format, unless you’re concerned about compatibility with devices manufactured prior to 2010.

Since both file types are being encoded by Amazon and Apple at an average bitrate of 256 kbits/second, their sound quality is essentially equal. The Apple AAC files are slightly larger, but not significantly so, which means file size is not a concern when choosing between file formats, either.

 

Coming Up Next In The Series: Amazon vs. Apple, Devices

 

 

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