Bob pointed to a YouTube video titled The Loudness War. The video uses Paul McCartney's 1989 song "Figure of Eight" as an example, comparing its original recording with what a modern engineer might do with it.
"It really no longer sounds like a snare drum with a very sharp attack," Ludwig says. "It sounds more like somebody padding on a piece of leather or something like that," Ludwig says. He's referring to the practice of using compressors to squash the music, making the quiet parts louder and the loud parts a little quieter, so it jumps out of your radio or iPod."
and Dr. Andrew Oxenham (of our fair University) explains it thus:
"Really, the challenge is to maintain the quality of a CD, but to stuff it into a much smaller space," Oxenham says. "Let's think about how digital recording works. You start out with a very smooth sound wave and we're trying to store that in digital form. So we're really trying to reproduce a smooth curve [with] these square blocks, which are the digital numbers [the 1s and 0s that are used to encode sound digitally].
"Now, the only way you can make square blocks look like a smooth curve is by using very, very small blocks so it ends up looking as if it's smooth. Now using lots and lots of blocks means lots of storage, so we end up using [fewer] bigger blocks. Which means we end up not representing that curve very smoothly at all."
"The difference between the smooth curve and the rough edges you end up with in the digital recording, you can think of as noise because that is perceived as noise," Oxenham says. "It's perceived as an error, something that wasn't there in the original recording. The trick is to take the noise -- which is the loss of fidelity -- and just make it so you can't hear it anymore."
"[The loud parts of the music are] giving the coding system a lot of leeway to code things not quite as accurately as it would have to," Oxenham says, "because the ear is being stimulated so much by the loud sound it won't pick up very small variations produced by the coding errors."