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> module RandomMusic where
> import Euterpea
> import System.Random
Generating music with random numbers
Last modified: 22-July-2016
Donya Quick
This example will illustrate the basics of using random numbers
to create novel musical structures with Euterpea. First, we'll
look at how to create infinite sequences of random numbers to use
as musical "inspiration," and then we'll look at mapping those
values to things we can hear.
The randInts function below will make an infintie series of random
Ints from a seed.
> randInts :: Int -> [Int]
> randInts seed = recInts (mkStdGen seed) where
> recInts g = let (i,g') = next g in i : recInts g'
This numbers from randInts will be over the entire range of the
integers, so we will need to take the modulo a base to keep them
in a more usable range. The function below creates a random
series of integers within a user-specified range.
> randIntsRange :: (Int, Int) -> Int -> [Int]
> randIntsRange (lower, upper) =
> map (\i -> (i `mod` (upper-lower)) + lower) . randInts
We can use this function to generate random pitches and volumes,
the standard MIDI range for each is 0-127.
The function below will create a random "melody" using a
specified random number seed, s. Each note will have the
duration of a sixteenth note (sn).
> melGen :: Int -> Music (Pitch, Volume)
> melGen s =
> let pitches = map pitch $ randIntsRange (30,80) s
> vols = randIntsRange (40,100) (s+1)
> in line $ map (note sn) $ zip pitches vols
Because Euterpea supports infinite playback, we can actually
listen to one of these melodies indefinitely! Try calling
the function below from GHCi:
> infinitePlay = play $ melGen 42
Finally we use this function to create three lines in parallel,
each affected by some Control options. To make this piece finite,
we will use Euterpea's "cut" function to take a fixed number of
measures from the otherwise infinite series that melGen produces.
Various Modify constructors are used to alter the performance of
each instrument's part: speeding up (Accelerando), slowing down
(Ritardando), and getting louder (Crescendo). The tempo (Tmp)
modifiers result in interesting rhythmic textures, such that the
voices do not play in lock-step.
> somethingWeird =
> let part1 = instrument Xylophone $ dim $ rit $ cut 6 $ melGen 345
> part2 = instrument Marimba $ cut 4 $ melGen 234
> part3 = instrument TubularBells $ cre $ acc $ cut 8 $ melGen 789
> in chord [part1, part2, part3] where
> rit = Modify (Phrase [Tmp $ Ritardando 0.5])
> acc = Modify (Phrase [Tmp $ Accelerando 0.5])
> dim = Modify (Phrase [Dyn $ Diminuendo 0.5])
> cre = Modify (Phrase [Dyn $ Crescendo 0.5])