OPN F-Num to frequency formula

[vampirefrog]

Y'all happen to have a formula or some code that converts from the OPN Block + F-Num to a floating point frequency value? And maybe the same for OPM? Thanks

[ctr]

For OPN series this might work based on the datasheet (though really not tested):

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Fc / 144 / 2^(10-Block) * Fnum / 2048

8000000 / 144 / Math.pow(2,10-4) * 1038 / 2048 = 439.9617513020833

For OPM you'll need a lookup table to convert the keycode to MIDI notes then you can do something like

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440 * 2^((kc - 56 + kf / 64)/12)

this example assumes note count starts at C#0 and A4 freq is 440hz. For this you might need to define a different reference frequency based on the chip clock. If you want to be completely accurate you need to use yet another lookup table that converts it to the internal F-num/block.

[vampirefrog]

Thx, that seems to work for OPN, haven't tried the OPM formula yet.