This Week’s Program: Dec 7 - Dec 11

Happy {Ch,H,Ḥ}anuk(k)ah! We’re several nights into the Festival of Lights and this week has been all about finding a rhythm. Literally. How do you teach a computer rhythm? I have a hard time (pun) with rhythm myself so you can imagine the challenge of programming a computer to stay on beat.

afcf6d793d129e2563fe3b67439ddbfc71f67de9

The first thing I do is bring in a sample of a simple kick drum from Freesound. Overtone provides all the tools needed to pull down a sample from Freesound and use it like any other synthesized instrument. This is pulled right out of Overtone’s documentation.

The next thing I do is exercise a common idiom seen in Overtone (and Extempore/Impromptu) called temporal recursion. Effectively, this means a function that schedules itself to be called again at some point in the future. Similar to tail call optimization, this means that you need not concern yourself with a growing stack. This is accomplished in Overtone with the at-at library and a collection of functions (including the after-delay function that I was using in earlier iterations). The at function is used to schedule messages to the SuperCollider server and apply-by schedules Clojure functions to be run in the future.

These scheduling functions are used in conjunction with Overtone’s metronome capabilities. The metronome is really just a time manager. You define a metronome by calling (metronome bpm) and it returns a function. When the returned function is called, it gives you a beat number and multiple calls will reveal that it’s just ticking along in the background. When you pass a beat number in as an argument to the returned function, it returns a timestamp of when that beat will hit. In this way the metronome just maps beats to clock time for the purposes of ahead-of-time scheduling.

I call this function like so:

(play-bars 4 (metronome 120) kick)

This is a lie. It doesn’t play 4 bars. Instead, it plays kick for 4 beats. I haven’t quite figured out the best abstraction for counting down bars. Overtone has functions metro-bar, metro-tock, and metro-bpb that are about mapping beats to bars. I’m not sure how relevant these are. My end goal is, given a list of lists of notes, treat each note list as a bar and when all the notes have been played, trigger some kind of event. I’m not sure if I’m trying too hard to cram the abstraction of Western notation into Overtone, but I’ll keep exploring. Also, if anybody wants to treat me to a lesson on music theory, I’m down.

The good news is this week I devised a real actual goal to accomplish by year-end: something to work toward more than just noodling.

I will leave you with this excellent video from Clojure Conj 2012 where Chris Ford uses Overtone to demonstrate how well the domain of music maps to a functional language. This is an incredibly well-done presentation and repeat viewings continuously provide me with inspiration and guidance.

Until next week.

🕎 Mark