These notes are extracted from the protracker 1.2 source.

Counter goes 1 .. 2 ... currentspeed ? -> 0
Actual commands occur for counter = 0

Finetune:
it seems the stored frequencies are actually notes, i.e., they
always correspond to the base frequency table.
So what you do is convert the frequency to notes as usual, then
use another frequency table according to the finetune setting.

Arpeggio 1: on Counter % 3 ,
	0 normal
	1 +HI
	2 +LO

Portamento up 1/down 2: there is NO default value. Accordingly, 0 does nothing.
Note that we ensure $71 <= period <= $358. And 0 <= volume <= 64

Tone portamento 3/Tone porta+ vol slide 5: work exactly the same way except that
5 doesn't have a rate, but use the previous rate.
Various cases:
- new note: porta to the new note with the given (or previous) rate.
Start with the current period, not any previous goal or anything.
- no new note: go on tone portamento, unless already finished. If needed,
adjust rate on the fly.
Gliss funk E3: snap the actual pitch to the nearest note. Don't store it.


Fine porta up E1/Fine porta down E2/Fine volume up EA/Fine volume down EB:
do just one change, on setup.

Set speed: under protracker, 0 does stop.
< 32 does a normal set counter.
>=32 is a factor to get real speed from (default is 125)

Change volume B: the value is pure binary.
Volume Slide A: delta = HI - LOW. No default value.
The actual code does: HI == 0 ? -LOW : +HI

Sample offset 9: take parameter x 256 and start from there (if
para x 256 >= length, just don't play sample).

Note cut EC/ Note Delay ED: occurs when counter= para

