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How Macs ‘see’ audio CDs.

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MajorFubar's picture
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I was messing around with an audio CD on my Mac last night and I noticed something rather interesting (well, interesting to me, but then I am a nerd).

On Windows, if you ‘explore’ an audio CD all you see are ‘.cda’ files which can’t be read or played as such. If you try to copy/paste them to a folder on your PC, you don’t get anything which can be read or played either (least not on my XP laptop, not tried on wifey’s Win7). I can appreciate why this is, because while Red Book is definitely not my specialist, I do understand at least the rudiments of how audio CDs are created and why they need to be ‘ripped’ to get audio off them in a data-format like WAV.

On my Mac, things are completely different. Open an audio CD on a Mac and you get a window of ‘.AIFF’ files which not only can be played in-situ with QuickView but can even be copied/pasted to another folder, just as if they were files on a data CD. Once copied, these too can be played and even edited.

I was wondering why Macs can do this, and what difference there would be between ripping the audio from the CD in a conventional way and just copying/pasting directly from the CD to a folder, other than the latter method won’t create any tags.

In fact I can see an experiment coming up later. I’ll rip a track from a CD losslessly, first using iTunes then using XLD, then just via a simple copy/paste, and we’ll see what differences there are.

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cheeseboy's picture
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RE: How Macs ‘see’ audio CDs.

some more info here to help understand http://www.fileinfo.com/help/cd_audio

 

Although the .aiff copy should be indentical to an uncomressed rip.

Mr.H's picture
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RE: How Macs ‘see’ audio CDs.

Macs can do this because they're better than horrid Windows PCs Wink There's just some invisible "clever" going on that presents the contents of audio CDs as .aiff files even though they aren't really .aiff files. It wouldn't surprise me if Windows Vista/7/8 does something similar; XP is very old.

In terms of differences ripping with iTunes/XLD vs. just copying in Finder, I would expect in the vast, vast majority of cases that there would be no difference whatsoever. Whether there would ever be a difference depends on how Finder handles errors - in iTunes there's an option to "rip CDs using error correction" - this reads the data as fast as possible but goes back and re-reads if it encounters an error. Finder may not do this.

Do let us know the outcome of your experiment. Try a few CDs in various conditions of wear, assuming you have some that are pristine and some not so pristine.

MajorFubar's picture
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RE: How Macs ‘see’ audio CDs.

Quick responses chaps thanks!

Mr.H wrote:
There's just some invisible "clever" going on that presents the contents of audio CDs as .aiff files even though they aren't really .aiff files.

Indeed, it's as though there is a kind of on-demand real-time conversion.

We'll see what differences there are, if any, when I get chance to have a go tonight. I do have a couple of CDs where the last track was troublesome for iTunes to rip successfully. It will be interesting to see how they copy via finder...

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MajorFubar's picture
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RE: How Macs ‘see’ audio CDs.

The results are in...

I've not tried a 'difficult' CD yet, but trying one track from a known good CD*, the iTunes rip (with error correction) and the direct copy/paste were absolutely identical in every way and passed the 'null test' in Audacity immediately. As usual the XLD rip was about 50-60 samples longer at the start but nulled with the other two files as soon as the timing was absolutely aligned.

So other than the XLD file being thousandths of a second longer at the start, all three files were completely identical.

 

*for anyone interested it was track 7, "End Title From The Boy Who Could Fly" on the 1990 CD "Fantastic Journey" by Erich Kunzel and the Cincinati Pops Orchestra, Telarc CD-80231

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Main system: Mac Mini 2011 • HRT II+ DAC • Lacie 3TB Cloudbox NAS • Marantz CD63KIS • Marantz PM66 KI • EB Acoustics EB2

In storage: Thorens TD160 (no cart) • Cyrus 2 + PSX • Cyrus tuner • Technics SL-P777 • Nakamichi DR-1