It's a bit more complex than that but yep, it's 1 sample every 144 cycles (and yes, the source clock is the same one used for the 68000 - which also means it varies depending on whether it's NTSC or PAL, but it's so minor that you'll probably just want to ignore it unless you're an audiophile).
I don't recall the details, but block is pretty much a bit shift left (since it's used to determine the octave - one octave/block up = multiply by 2). As for frequencies, this is what Echo uses for each pitch (from C to B), although it's a blend of the frequencies of NTSC and PAL speeds:
Code:
FMFreqTable:
dw 644, 681, 722, 765
dw 810, 858, 910, 964
dw 1021, 1081, 1146, 1214
The maximum is 2047 so you have to resort to blocks to move onto the next octave =/ (you can use lesser values for going down, although you lose some precision)