It's to do with compression and one of my best pals who is a sound engineer for Universal
and thus knows more about this than anyone on here ever will says it's blindingly obvious to him if he's listening to an MP3 as opposed to a record or reel-to-reel tape.
( Monty Boyce, My cheese game is strong, Mon 2 Jul 2012, 10:48, 5 replies, latest was 13 years ago)

Ah, yeah, when a file's compressed you get data loss in the top frequency range
Tends to kill the treble. Depending on the quality of encoding, most people aren't going to be able to tell the difference, though, as a lot of it's outside the human hearing range anyway. Most consumer equipment does more damage to the signal than mere compression, so for the average person it's meaningless.

I do agree that compression would be no use whatsoever for reference quality stuff.
( Kroney, Mon 2 Jul 2012, 10:53, Reply)

In the late 90s there was a trend for massive over compression of CDs
In order to try to make them louder for radio play. It tended to make everything sound a bit shit.
If you're interested in this sort of thing you should read Perfecting Sound Forever, by Greg Milner. It is surprising interesting for a subject that could easily be very dull.
( tangledupinblue hairy badge with moving eyes, Mon 2 Jul 2012, 10:57, Reply)

It's funny really
Because a CDs got plenty of room on it, there's no actual need to compress the files.

As for whether I'm interested in it, I often wish I'd gone into sound engineering myself.
( Kroney, Mon 2 Jul 2012, 11:02, Reply)

That's nothing to do with comrpession to get it onto the CD
that's the mastering process where everything is compressed so every part of the sound wave is the same "loudness" and it's still going on to this day. It leads to all songs having no dynamic balance.
(Bazongaloid, Mon 2 Jul 2012, 11:06, Reply)

That was roughly what I was about to reply to Kroney above
This picture show the same audio, the top one is compressed, the bottom one is the original file:

( tangledupinblue hairy badge with moving eyes, Mon 2 Jul 2012, 11:11, Reply)

The top one looks like a Gallagher eyebrow

( sporters I’m sincerely gratitude to you, Mon 2 Jul 2012, 11:13, Reply)

The whole of Death Magnetic was slightly over compressed.
Which is annoying.
(Bazongaloid, Mon 2 Jul 2012, 11:14, Reply)

Morning hippy.
How was the weekend? As I recall, you were planning on getting totally muntered. Succeed?
(Bear Pookie The Frankly Challenged. Halloween is coming to town., Mon 2 Jul 2012, 10:56, Reply)

Unless it's losslessly compressed
in which case it'll be more or less identical.

but you need a format other than mp3 for lossless compression.
( the mighty badger Aphrodite, on a bar stool, by your side, Mon 2 Jul 2012, 10:58, Reply)

and the file size tends to be a bit bigger

(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Mon 2 Jul 2012, 10:59, Reply)

a hell of a lot bigger, yep.

( the mighty badger Aphrodite, on a bar stool, by your side, Mon 2 Jul 2012, 11:20, Reply)

it's not all about size

(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Mon 2 Jul 2012, 11:22, Reply)

I know someone who's a professional wine taster,
I don't ask him for advice on good wine anymore because his tastes are so attuned to wine I'd end up spending £40 more than i would have and barely noticed a difference.
(PsychoChomp, Mon 2 Jul 2012, 11:03, Reply)

Plus, like some many things, it's entirely subjective.
The only reason some wines get great write ups from famous wine critics is because the wine makers make wines that they know the critic will like. But that doesn't mean you would like them.
(Bazongaloid, Mon 2 Jul 2012, 11:07, Reply)

i don't think they'd make them if only one person liked them
there's not an awful lot of profit in that
(Quintno EXPERIMENT RUINED CANCELLED, LEFT 4EVER, Mon 2 Jul 2012, 11:09, Reply)

He may say that
but he is wrong. If you put him in a room with a reasonable quality seperates system and a VBR comrpessed mp3 vs a CD he couldn't tell the difference.
(Bazongaloid, Mon 2 Jul 2012, 11:04, Reply)

I'd be far more likely to believe the word of a professional sound engineer
over that of a guy that regularly reads What Hi-Fi? I am including myself in that latter category.
( Kroney, Mon 2 Jul 2012, 11:09, Reply)

A professional sound engineer listening through professional quality equipment would have a fighting chance at differentiating between the two
but the effects of compression are completely negligible when listening through a bog standard hi-fi separates system.
(Bazongaloid, Mon 2 Jul 2012, 11:13, Reply)

Yeah, I said something similar above.
Monty did say mp3 versus vinyl/reel to reel, though. Not mp3 vs CD.

Even so, if a guy that's spent however many years listening to sound for a living says there's a difference, I'd be inclined to believe him even if I personally can't hear it.
( Kroney, Mon 2 Jul 2012, 11:15, Reply)

Of course there is a difference, the technical specs prove that.
But the question is, can you hear that difference, and the answer is no. Unless, you are in a near perfect environment with a near perfect system. Since that situation will virtually never arise, the answer, to all intents and purposes, remains No.
(Bazongaloid, Mon 2 Jul 2012, 11:19, Reply)

I know a lecturer in acoustics,
and in his opinion, the difference in home quality cd/dvd/vinyl is so small, it's just not worth pissing about. It's only when you spend thousands, position your chair specifically, dampen the walls etc that you will notice a difference, but it all sounds a bit much effort.
(Bear Pookie The Frankly Challenged. Halloween is coming to town., Mon 2 Jul 2012, 11:24, Reply)

Exactly
which is why I have no respect at all for hifi aficionados that spend hundreds of pounds on equipment and cables for their house.
( Kroney, Mon 2 Jul 2012, 11:33, Reply)