pitch slide on mod - protracker

[Zenon]

I still not quite understand how pitch works on protracker format.
That is, with a TPR of 06, a G-5 note will slide up to about a A-5 note with a 106 command (it's good for me, because 06 * (6-1) = 30, that is close to 32/32.
This is not the same with a G-4 note, in which I need a 10D param to reach A-4 note. Why?

[Zenon]

It indeed depends on amiga frequency table.

I wonder if there's a way to compute the right value for the note to reach

[Saga Musix]

It's easy if you work with periods (approximately the inverse to frequency)... Basically the slide value is a period value (*4 if you're using extended Fasttracker period tables)... Since the period is inverse to the frequency, the parameter becomes more "effective" in the higher octaves as the distance in Hz between f.e. C-5 and C-6 is smaller than f.e. C-3 and C-4... Hope that helps a bit.

[Zenon]

I read a wiki page here.

Technically, with 1xx or 2xx you have to decrement/increment the period by $x value * (tpr-1).

Therefore, if you have the protracker period table, it's possible to achieve the exact destination period.

For example, if C-4 is 856, to obtain a closer value to C#4 (period 808) with TPR=6, the right portamento value is 9

formula is (856 - 808) / 5 = 9.6.

Is it right ?
Thank you

[Saga Musix]

Sounds correct...