noise, the 4006 and an xor

[Echophazer at aol.com]

I have a circuit that a friend passed on to me that uses a 4006 shift 
register, cd4070 Quad XOR and the VCO section of a 4046. I'm sure someone has 
seen this before. I don't quite understand how the shift register and XOR 
gates do the things they do. This was a partially completed project of his 
and I have no schematics for the whole synth. If anyone knows a source to 
schematics for a noise circuit like this I'd also be appreciative.
Peter B