I just made my first Vic-20 sound sample (and player)..
I didn't have a PC program that would convert 8-bit samples down to 4-bit, so I just used a basic program to divide all 8-bit values by 16, and it worked perfectly!
http://www.adam.com.au/grichards/jibber.prg
'The wit and wisdom of Mr T' - recorded from a keyring I have..

Requires 8K memory expansion..
SYS5120 to play the sample - sounds much better on a real VIC than on my PC using VICE.. (now that I have a new VIC chip anyway..)
This is a 6000Hz sample, using 1 nibble per byte, so should at least be able to halve the size of the wav file..
Loads of fun..
-G