Simple synth

gistfile1.txt

-- public domain
-- author: LPGhatguy

local default_samples = 48000
local pitch_rate = 2^(1 / 12)

local function round(n)
  return math.floor(n + 0.5)
end

local function hertz(semitones, base)
  base = base or 220
  return base * pitch_rate ^ semitones
end

local function build_tone(frequencies, samples)
  samples = samples or default_samples

  local data = love.sound.newSoundData(samples, samples, 16, 1)
  local scalars = {}

  for index = 1, #frequencies do
    local frequency, amplitude

    if (type(frequencies[index]) == "table") then
      frequency = frequencies[index][1]
      amplitude = frequencies[index][2] or 1
    else
      frequency = frequencies[index]
      amplitude = 1
    end

    scalars[index] = {math.floor(frequency + 0.5) * math.pi * 2 / samples, amplitude}
  end

  for pos = 0, samples - 1 do
    local sum = 0

    for index = 1, #scalars do
      sum = sum + (scalars[index][2] * math.sin(pos * scalars[index][1]))
    end

    data:setSample(pos, math.min(1, math.max(-1, sum / #frequencies)))
  end

  local wrapper = love.audio.newSource(data)
  wrapper:setLooping(true)

  return wrapper
end

local tones = {}
local fading = {}

local keys = {
  a = -3,
  z = -2,
  s = -1,
  x = 0,
  d = 1,
  c = 2,
  v = 3,
  g = 4,
  b = 5,
  h = 6,
  n = 7,
  m = 8
}

function love.update(delta)
  for key, value in pairs(fading) do
    value:setVolume(math.max(0, value:getVolume() - delta * 1.3))

    if (value:getVolume() <= 0) then
      value:stop()
    end
  end
end

function love.keypressed(key)
  if (keys[key]) then
    local semitones = keys[key]

    if (not tones[semitones]) then
      tones[semitones] = build_tone({
        {hertz(semitones), 1},
        {hertz(semitones + 12), 0.937},
        {hertz(semitones + 19), 0.960},
        {hertz(semitones + 24), 0.863},
        {hertz(semitones + 28), 0.889},
        {hertz(semitones + 31), 0.789}
      }, 192000)
    end

    if (fading[semitones]) then
      fading[semitones] = nil
    end

    tones[semitones]:stop()
    tones[semitones]:setVolume(0.5)
    tones[semitones]:play()
  end
end

function love.keyreleased(key)
  if (keys[key]) then
    local semitones = keys[key]

    if (tones[semitones]) then
      fading[semitones] = tones[semitones]
    end
  end
end