hammy.lua

-- Calculates some kind of hammond tuning
-- See https://electricdruid.net/technical-aspects-of-the-hammond-organ/


local Ratios = {
	{85, 104},
	{71, 82},
	{67, 73},
	{105, 108},
	{103, 100},
	{84, 77},
	{74, 64},
	{98, 80},
	{96, 74},
	{88, 64},
	{67, 46},
	{108, 70}
}
local rotorSpeed = 20

--- Calculates a "hammond" tuned MIDI pitch.
-- @param note A MIDI note pitch 0-127
-- @returns Tuned MIDI note pitch (float)
function tune(note)
	numTeeth = 2 ^ ((note // 12) - 1)
	abRatios = Ratios[(note % 12) + 1]
	freq = rotorSpeed * numTeeth * (abRatios[1] / abRatios[2])
	return freq2note(freq)
end


--- Converts a frequency to MIDI note.
-- @param freq A The frequency
-- @returns A MIDI pitch (something between 0 and 127).
local function freq2note(freq)
	return 12 * math.log(freq / 440) + 69
end