I bought Chef Aid: The South Park album years ago. Great album, love it to bits and every so often still listen to it. However Track 18 always bugged me - Chef's vocals alternate between crystal clear studio quality and some dingy, Skypesque highly compressed garble (in reality probably closer to a 64 kbps ISDN codec).
These days I'm a qualified sound engineer and technician but I was always 'into' production, sound quality etc. I picked up on the weirdness of Track 18 from first listen but could never find anyone to ask or discuss it with. However Scott Smitelli outnerded me to the punch (in 2007) and wrote an entire article on his web site - with empirical evidence, good work that man! In his article he explains the differences between the portions of vocals contributed by Isaac Hayes and really goes into quite a lot of depth before coming to his own conclusion as to why the sound is as it is. Kudos to him... Because now when I'm talking to people about this I can just reference his page instead of explaining again from scratch. 😉
His article about the strange audio on Track 18 of Chef Aid is on his web site - go read if you're a fan of the album.
An' tha's yer lot fer now...