[Coco] Speech & Sound Pak - carrier frequency of stock voice?

[Phil]

Hi, all --

What determines the frequency of the carrier wave in the stock voice 
of the Speech & Sound Pak?  It sounds like it's about 220 Hz, or at 
least (from what I remember) it's tuned to the pitch A-natural.  Can 
it be changed with a well-placed POKE?  It'd be fun to make the Coco 
"sing", a la "Bicycle Built For Two".

By "stock voice", by the way, I mean the voice you get when typing in 
the program that's at the front of the Speech & Sound pak manual -- a 
program that I must've typed in by hand at least 20 times over the 
years!  I had no Multi-Pak interface, though I suppose I could've 
saved it to cassette...

Thanks --
Phil