Karplus-Strong 'piano' for love2d

local SAMPLE_RATE = 44100

-- Karplus-Strong generator

local function tick(buffer, attenuation)
  local previous_position = buffer.current
  local first = buffer[buffer.current]
  buffer.current = buffer.current + 1

  if buffer.current > buffer.n then
    buffer.current = 1
  end

  local second = buffer[buffer.current]
  local value = attenuation * (second + first) / 2
  buffer[previous_position] = value
  return value
end

local function create_buffer(frequency)
  local buffer_size = math.floor(SAMPLE_RATE / frequency + 0.5)
  local buf = {}
  for i = 1, buffer_size do
    buf[i] = math.random(-1, 1)
  end
  buf.current = 1
  buf.n = buffer_size
  return buf
end

local function generate_sound(frequency, length, attenuation)
  local sound = {}
  local ringbuffer = create_buffer(frequency)
  local length_in_samples = length * SAMPLE_RATE
  for i = 1, length_in_samples do
    sound[i] = tick(ringbuffer, attenuation)
  end
  return sound
end

-- Convert array to love2d's SoundData
local function array_to_sound_data(array)
  local data = love.sound.newSoundData(#array, SAMPLE_RATE, 16, 1)
  for i, v in ipairs(array) do
    data:setSample(i-1, v)
  end
  return data
end

local attenuation = 1
local notes = {}
do
  local base_frequency = 200
  local keys = {"q", "2", "w", "3", "e", "r", "5", "t", "6", "y", "7", "u", "i"}
  for i, key in pairs(keys) do
    notes[key] = base_frequency * math.pow(2, i/12)
  end
end

function love.keypressed(key)
  if key == "up" then
    attenuation = attenuation + 0.01
    if attenuation > 1 then
      attenuation = 1
    end
  elseif key == "down" then
    attenuation = attenuation - 0.01
    if attenuation < 0 then
      attenuation = 0
    end
  end

  local frequency = notes[key]
  if frequency then
    local sound = generate_sound(frequency, 5, attenuation)
    local soundData = array_to_sound_data(sound)
    local audiosrc = love.audio.newSource(soundData)
    love.audio.stop()
    love.audio.play(audiosrc)
  end
end