ALAC not always lossless (converting in iTunes)*

Discussion in 'Audio Hardware' started by Mono is louder., Jan 20, 2014.

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  1. Mono is louder.

    Mono is louder. Forum Resident Thread Starter

    Location:
    London, UK
    Has anybody else here converted a 192 kHz/24-bit wav file to ALAC in iTunes?

    After re-converting back to wav, do you find a significant drop in bit rate?


    Here's an example:

    "Little Lies" from Tango in the Night - Fleetwood Mac downloaded from HDtracks at 192 kHz/24-bit in wav format. (I understand that HDtracks offers ALAC files, but hey ho)...

    iTunes correctly displays the bit rate for this 192/24 wav file as 9216 kbps. The file is 243.3 MB in size.

    If I convert this to ALAC using iTunes' in-built conversion tool (right click --> Create Apple Lossless Version) I end up with an ALAC version which has a bit rate of 5327 kbps at a size of 140.7 MB - as expected.

    However, an interesting thing occurs if I convert this ALAC file back to wav using the same process as above. I select wav in iTunes' Import Settings using the "Automatic" setting. I right click the ALAC file and select Create WAV Version and I end up with a shiny, new wav file except rather strangely with a bit rate of 6144 kbps and a size of 162.2 MB. Somewhere along this chain of events, the lossless conversion breaks down.

    Even more bizarre is the fact that if I convert this final, butchered 6144 kbps wav file back to ALAC, I get an ALAC file with a bit rate of 2252 kbps - 59.6 MB, but when I convert it back to wav again, I get the identical 6144 kbps wav back again!

    To top it all off, the problem is not only present with ultra-high bit rates over 7000 kbps say, as I tried the above experiment with a 96 kHz/24-bit wav file with the same results. The original 96/24 wav file had a bit rate of 4608 kbps as expected. When converted to ALAC the bit rate was reduced to 2762 kbps, and when that ALAC file was converted back to wav again, the bit rate was 3072 kbps. From then on, it doesn't matter how many times I convert it to ALAC and back again, I always end up with the same 3072 kbps wav file.
    Does anybody here have any idea whatsoever as to what is going on? (Besides "iTunes is crap" etc.) I am aware that there id probably better software out there to manage a high resolution music library, but surely the lossless digital algorithms in iTunes should still work with absolutely no change in the quality of the data.

    The only explanation I can figure out is that although iTunes is compatible with hi-resolution audio files and can play them back bit-perfect, the settings within the "Import Settings" dialogue are far less encouraging. If I select "WAV Encoder" and change the "Automatic" setting to "Custom," I am greeted with yet another dialogue with three drop-down menus. Sample Rate with options only up to 48,000 kHz, Sample Size with options only up to 16-bit(!) and Channels (mono or stereo).

    So does this mean that anything with a sample rate over 48 kHz and a bit depth of 16bit is not converted losslessly within iTunes? If so, what the deuce? Is there a loss in data in the first conversion to ALAC? Or does the problem only exist when converting to wav - since the ALAC encoder may support 24-bit files with sample rates over 48 kHz. There are no settings in the "Import Settings" tab when ALAC is selected other than Automatic, so I guess there's no way to be sure...
     
  2. pscreed

    pscreed Upstanding Member

    Location:
    Land of the Free
    Of course the ALAC format is lossless. What is obviously not resulting in a bit perfect conversion is the experiment you are performing. Not sure why you would be downloading .wav files instead of ALAC, if that's your target format... But whatever.

    If you really need to do these chains of file conversions, try something besides iTunes. I like this one:

    http://www.monkey-tools.com/products/sound-grinder/
     
  3. Ulli

    Ulli Forum Resident

    Location:
    Germany
    I don't use iTunes, just want to point out that 6144 kbps is the bitrate of 192 kHz/16 bit stereo PCM. That might give you a clue what iTunes is doing behind your back.
     
  4. mwheelerk

    mwheelerk Sorry, I can't talk now, I'm listening to music...

    Location:
    Gilbert Arizona
    Try a standard 16/44.1 WAV file going through the conversion process you used. Compare the results. If the same anomalies exist there would be a concern with the overall performance of the iTunes ripping tool. If not the issue lies with 24 bit files. Try the same comparisons in another ripping tool like XLD or EAC (Mac or Windows). What are the results using the same files and process with another tool?
     
  5. Steve Martin

    Steve Martin Wild & Crazy Guy

    Location:
    Plano, TX
    You might try xACT to do your Apple Lossless to WAV conversion. Maybe iTunes doesn't support 24-bit WAV for some reason?
     
  6. Synthfreek

    Synthfreek I’m a ray of sunshine & bastion of positivity

    I don't find this weird at all. When you converted to WAV after the initial conversion to ALAC iTunes simply used the highest settings it can muster for a WAV file which is 16/48. AT THAT POINT you are going to get the same file sizes when you transcode them back and forth.
     
    Billy Infinity and pscreed like this.
  7. rodney sherman

    rodney sherman Forum Resident

    Location:
    de soto, kansas
    ITunes will only convert 192/24 apple lossless to 48/16 wav on the automatic setting. I take the 48/16 wav file and convert it to apple lossless. After that I edit the album title. Here is a screen shot.
     

    Attached Files:

  8. gloomrider

    gloomrider Well-Known Member

    Location:
    Hollywood, CA, USA
    A handy calculator is here.
     
  9. rodney sherman

    rodney sherman Forum Resident

    Location:
    de soto, kansas
    ITunes will always convert WAV files at 192/24 all the way down to 44.1/16 to apple lossless with no loss. but if you convert WAV. AIFF. M4A from 192/24 thru 48/24 to WAV again it will be no higher than 48/16. Its the default of the iTunes converter. To sum it up 192/24 WAV will convert to apple lossless and stay 192/24. 192/24 WAV will convert to 48/16 WAV.
     
    Last edited: Jan 20, 2014
  10. gloomrider

    gloomrider Well-Known Member

    Location:
    Hollywood, CA, USA
    I suspect there are not many lovers of command line utilities, but the Open Source "alac" command will convert 192/24 ALAC files to 192/24 WAV files all day long. :thumbsup:
     
  11. rodney sherman

    rodney sherman Forum Resident

    Location:
    de soto, kansas
    I use JRiver mc19 and it does not down sample files when converting at all.
     
  12. numanoid

    numanoid Forum Resident

    Location:
    Valparaiso, IN
    If you're on a Mac, why not use Max or XLD? Very easy to use, great results, and lots of customization. If you're on Windows, you have thousands of options. iTunes is made out-of-the-box for your Grandma to use and get results. And no, that's not an insult to iTunes, most settings default to what most people want or expect. I suspect not many people are trying to play 24/192 files with iTunes, which is why your options are limited in the program.
     
    Billy Infinity and Vidiot like this.
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