In general, algorithmic compositions using piano instruments always strike me for their captivating simplicity. So here's a new little experiment, titled 'Piano Scales'.
The gist of this musical algorithm is amazingly simple.
Pick a scale. You play it using a variable time-interval between its notes, which is determined by a cosine function (cosr). The variable interval gives the final result a touch of suspense and makes it less computer-like.
(define xsc
(lambda (beat vel scale)
(let ((dur (cosratio 4 2 1/128)))
After each note, more notes are played programmatically, after brief (random) intervals of half a beat, or 3/2 of a beat. Fifths, octaves, minor sevenths... as you please.
This whole thing repeating itself, at each iteration of the loop though the sound volume gets quieter by a fixed amount. Eventually, when the volume goes to 0, the repetition stops.
(define xsc
(lambda (beat vel scale)
(let ((dur (cosratio 4 2 1/128)))
;; piano
(play (car scale) vel dur 1)
(play 5 (+ 12 (car scale)) 1 (* dur 2) 1)
(play (oneof 3/2 2) (+ 24 (car scale)) 1 (* dur 2) 1)
;; bass
(play 5 (car scale) 90 (* dur 2) 2)
(:chance .8 (play 6 (+ (car scale) 2) 90 (* dur 2) 2))
;; repeat
(set! scale (rotate scale -1))
(set! vel (- vel 1))
(if (> vel 0)
(callback (*metro* (+ beat (* 1/2 dur))) 'xsc
(+ beat dur)
vel
scale)))))
;; set scale to play so that scales overlap with each other
(xsc (*metro* 'get-beat 1)
50 ; vol
(:mkscale c1 'pentatonic 2))
;; run again with 'ionian, 'aeolian etc.. for interesting harmonic effects
The full source code on GitHub.
Extempore is a programming language and runtime environment designed by Andrew Sorensen to support livecoding and cyberphysical programming, where a human programmer operates as an active agent in the world.
Algorithmic composition is the technique of using algorithms to create music.
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