On 10/05/2011 05:23 PM, Darren New wrote:
> On 5/10/2011 8:32, Invisible wrote:
>> 1. Why the hell would you put compressed audio onto a CD rather than the
>> uncompressed original source?
>
> Because you don't have the original source, or the person mastering the
> CD got the original source over a network and didn't want to spend the
> bandwidth and didn't care?

I can only imaging it was the latter. This particular CD is modern 
electronic dance music, after all.

> There are lots of CDs out there that were copied off vinyl albums that
> weren't properly compensated and have the treble turned way up. (Vinyl
> turns the treble up, and the record player turns it back down, to reduce
> hiss.)

The other day, I was listening to a CD of vintage music, and a suddenly 
noticed that most of it is monophonic. Imagine that! ;-)

>> 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?
>
> No. You can tell someone is talking over a telephone by the fact that
> too much information is lost. Same with autotune.

You can't tell that information has been lost unless you can tell that 
it was there in the first place. And if you can tell there's something 
missing just by looking at what's still there, there's redundancy.

>> 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.
>
> Sounds like nyquist limits screwing up the codec, to me.

Take any piece of sound. Apply too much MP3 compression. You can hear 
the quantinisation steps in the signal levels.

This isn't that bad, of course. You have to listen fairly hard to hear 
it. Then again, I'm the sort of person who owns a £100 set of headphones 
and a £300 CD player, so...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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