iTunes High Resolution Conversion to WAV or AIFF Truncates Bit Depth

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I spotted something surprising today, and if you buy and listen to high-resolution files with iTunes, you’ll want to know about this. Personally, I don’t believe the high-resolution music file stuff, but it’s up to you.

As you may know, you can play back high-resolution files in iTunes, if they are in Apple Lossless format. You can convert files to Apple Lossless from FLAC, AIFF or WAV with no loss in quality. You can do the WAV or AIFF conversion in iTunes, or, to convert FLAC files, you can use the free XLD.

But, if you use iTunes to later convert your Apple Lossless files to WAV or AIFF, you may be surprised: iTunes converts your 24-bit files to only 16 bits. Here’s an example: I took a 24-bit, 96 kHz file and converted it to WAV using iTunes. Here’s the original file:

001.png

And here’s the WAV file:

002.png

I’d always thought that iTunes was transparent in lossless encoding and decoding, but this is not the case. The same thing happens when converting to AIFF.

iTunes can play files at a bit depth of up to 24 bits, and with a sample rate of up to 352.8 kHz, assuming you have the hardware to handle that sample rate. But we forewarned that, if you plan to convert these lossless files back to AIFF or WAV, you’ll lose some of the high resolution. (To be fair, there is no reason to do so…)




4 replies
  1. Anthony Aaron says:

    Interestingly, as the bit-rate goes from 24 to 16, the file size increases from 19.6 MB to 22.1 MB. I wonder why this happens.

    Reply
  2. mark says:

    I didn’t realize AIFF or WAV even supported a 24 bit sample size, figured it was 16 bits or less.

    Reply

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