I ordered a copy of Vangelis's 'Spiral' from Amazon, without understanding that it was manufactured on demand by Amazon. That is, a CD-R. And not a high quality one either. This miffed me a bit - CDs haven't proven to be the best archival medium, CD-Rs are far worse. But that was, largely, my fault for not thoroughly reading the product description and spotting the tiny disclaimer that it was MoD. Acknowledging my responsibility in the matter, I was fully willing to keep the disc - at worst, I figured, it was just a horribly inefficient delivery method for ALAC.
Then I ripped it. There was all sorts of audible popping, and bizarre noise that I would best describe as digital artifacts. Buying this from Amazon also got me the 'Auto-Rip' copy, so a free MP3 download/stream from Amazon's Cloud Player. The MP3s sounded great after hearing the CD. I opened both up in Audacity. Where the MP3 had smooth curves, the CD flattened into squares. I don't really know what terrible mastering mistake would cause this - some sort of quantizing gone awry?
Both images have the CD up top and the MP3 down below. The first is two separate pieces of the same track - I should not have used the same color as the waveform to separate them, but I did. The first image shows this 'squaring off' of waves, while the second one shows just some seemingly random pops that should not be in the track.
This has nothing to do with CDs, per se, nor even (necessarily) Amazon's MoD process. But I don't like the increasing lack of attention and care that seems to be going into masters, etc. these days. Amazon claims the info is 'lossless,' from studio masters, from the label. But something, somewhere went horribly wrong and nobody caught it. The above disc should never have been sold to a consumer. I did return it (with no issues), and bought an original used copy instead.