> I've got a CD at home. When I first got it, I noticed that certain
> passages sound very slightly strange. Today, ten years later, I know
> exactly what it sounds like: it sounds like lossy audio compression.
>
> This raises two interesting questions:
>
> 1. Why the hell would you put compressed audio onto a CD rather than the
> uncompressed original source?

Maybe that the original recording was done in a lossy format, or even a 
non-lossy format but with a sample rate set to low and a sample 
resolution also to low... Like 4000 kHz (or even less), 4 bits...
(I had a single CD that contained the whole Beatles discography encoded 
as .wav at that level or about...)

>
> 2. If I can tell that it's compressed, despite not having the
> uncompressed original to compare to, doesn't that mean that there's more
> redundancy in the signal than the codec is taking advantage of?

It's just that you have reasons to expect a higher chromatic range than 
the one you have.
If it sound like speech but misses the harmonics that are normaly 
present and expected, it will sound suspicious or strange.
Same thing for any known musical instrument's sounds.
If there is some sampling of previously heard peices, you also can 
perceive the lacking parts.

>
> Now I don't actually know which codec was used here. [Asking whether you
> can tell the codec by the compression artefacts is another interesting
> question.] But in this instance, there are long echo tails which are
> getting audibly chewed up. Not drastically so, but enough to be noticeable.

Even the best codec set at the highest quality can't do miracle if the 
source is bad...

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