-- | Glues audio files together sequentially. Can also adjust volumes.
concatenate' :: (KnownNat r, KnownNat c) => [(Double, Audio r c)] -> Audio r c
concatenate' []    = silence
concatenate' :: (KnownNat r, KnownNat c) => [(Double, Audio r c)] -> Audio r c
concatenate' []    = silence
concatenate' []    = silence