if not SanicSpeedBoost then
  _G.SanicSpeedBoost = {}

  SanicSpeedBoost.volume_fp = 1 -- first person audio volume multiplier
  SanicSpeedBoost.volume_tp = 2 -- third person audio volume multiplier

  blt.xaudio.setup()
  -- changed buffer to contain multiple sounds here
  SanicSpeedBoost.buffer = {}
  SanicSpeedBoost.buffer[1] = XAudio.Buffer:new(ModPath .. "sound1.ogg")
  SanicSpeedBoost.buffer[2] = XAudio.Buffer:new(ModPath .. "sound2.ogg")
  SanicSpeedBoost.buffer[3] = XAudio.Buffer:new(ModPath .. "sound3.ogg")
  SanicSpeedBoost.buffer[4] = XAudio.Buffer:new(ModPath .. "sound4.ogg")
  -- till here

  function SanicSpeedBoost:play_sound(unit, third_person)
    if not alive(unit) then
      return
    end
    local u_base = unit:base()
    if not u_base._sanic_last_t or u_base._sanic_last_t < Application:time() + 8 then
      u_base._sanic_last_t = Application:time()
      -- changed following line to randomly play one of the sounds
      local src = third_person and XAudio.UnitSource:new(unit, SanicSpeedBoost.buffer[math.random(4)]) or XAudio.Source:new(SanicSpeedBoost.buffer[math.random(4)])
      if not third_person then
        src:set_relative(true)
      end
      src._gain = third_person and SanicSpeedBoost.volume_tp or SanicSpeedBoost.volume_fp
    end
  end
end