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Testing the CD transport quality

January 31, 2012

After reading all the stories about how the belt drives and the plate weight and blablabla influence the sound quality of the audio provided by a CD player I decided to make a simple test that would tell me with some degree of confidence whether that’s actually true or just kool-aid for the unsuspecting (and rich) audiophile.

The test

The test is very simple:Rip the same CD using several different CD drives hooked to different PCs. Since the WAV files you get when ripping is what’s exactly fed to a DAC in a CD transport If the assertions were true I would see one or more of the following:

  • Variations in the PCM samples between rips in the same machine
  • Variations in the PCM samples between rips from different machines (and different CD drives as a consequence)
  • Errors reported by the extraction software

If the assertions were not true then I would expect the PCM samples to be identical everywhere.

So I picked up a shiny new CD (bought a month ago or so) and ripped it using CDEAX on my three-year old laptop with one of those crappy loading mechanisms were the optical unit is part of the tray assembly hence prone to extra mechanical stress compared to a those regular CD drives found in most desktops.

The ripping went through without any errors so then I proceeded to calculate the MD5 hash of the file and kept it around.

Then I re-ripped the same track several times on the same laptop and drive and always the rip came without errors and the WAV file was identical to the first one.

Then I walked to my mini-tower PC and its two-year old standard CD drive and repeated the same process. Again the same results: no errors and no variations.

So then I took both files and compared them sample by sample.

Results

One sample was zeroed out in the WAV coming from the laptop. Everything else matched.

So what conclusions can we gather from this very small sample size?

  • Some CD drives introduce errors in the PCM samples without any kind of notification to the user except of course if the errors are so many that they become audible.
  • If it’s of reasonable quality the CD optical unit and mechanism won’t introduce any errors in the PCM samples
  • I doubt that one sample would be noticeable by the human ear although I can’t confirm this
  • The pink pony stories about the motor drive and the plate and blablabla are indeed kool-aid stories

Now the DAC, that’s another story but as long as the drive feeds it the same samples every time there’s no real need to use anything exotic to spin the disk and read the audio from the CD unless of course the driving used when reproing audio is that different than the one used when extracting it directly.

And even then I’d assume that extracting the PCM samples requires more precision since the disk is spinning way faster.

So… if you use CDs a lot invest your money in a good DAC and with the change buy a cheap PC with a reasonably good CD drive (SONY) and lots of storage and rip all your CDs to a lossless format (FLAC, WMA, …, or WAVs if you don’t care about space) and for listening just connect the PC to the DAC and use any player of your preference that can direct it’s output to any of the digital devices (i.e. foobar2000) and configure your software stack to avoid any upsampling.

At this point though I don’t know which connection would yield the less amount of jitter (USB, TOSLink or S/PDIF).

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From → Audio

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