Tell your friend his car computers look sweet. The fabrication of the replacement dash plate on the Z is particularly nice.

As far as the quality discussion goes... I actually commented on this in another thread with Mike... When I talk about high-frequency artifacts, they always seem to manifest themselves in high-frequency noise. In other words, the very thing that's hardest to compress. And the kinds of artifacts I notice happen in parts of the music that are particularly saturated with high-frequency noise. It seems that a 128kbps encoder can handle some high-frequency noise reasonably well, but not too much of it. So you only end up noticing it on certain songs.

Your friend's theory of the possible inconsistencies in a digital sample is known as jitter correction and it's already taken into account at each stage of the MP3 creation process: By the digital master of the original CD, by the drive mechanism you ripped the CD with, by the encoder, and by the playback firmware. Note that "jitter correction" is used two different ways: The first (and the correct usage), refers to the time-base correction of digital samples and their relative accuracy to a given wave. The second (and technically incorrect usage) refers to the ability of a CD ripper to sector-synchronise and correct errors when performing Digital Audio Extraction from a CD. Bad jitter correction can, as he predicted, cause artifacts that sound similar to compression artifacts. But that's not what's happening with a 128kbps MP3.

Here is a very well-informed discussion about jitter correction as it relates to digtally-sampled waveforms, and here is a discussion about jitter correction as it relates to ripping audio data blocks from a CD.

I have heard that data-compressed music fails to capture certain subtleties that audiophiles can notice. For example, the phrase "not enough air around the instruments" keeps coming up. I can't hear this myself-- perhaps it's the nature of the music I listen to. But that same phrase seems to get used in reference to jitter correction problems, too, so there's some sort of parallel going on. In the end, both jitter problems and data compression can make the final output sound slighty different from the original source, and therefore might induce the same sorts of audible artifacts.

Tony Fabris
Empeg #144