BitShift Variations in C Minor

This is a story about music composed by a computer, and collaboration between many individuals, each of whom has extended the work of their predecessor.

BitShift Variations

The original BitShift Variations in C Minor is a composition generated by code written in C by Rob Miles. It’s an extremely short yet amazingly complex piece of code, written for a “code golf” competition. Here’s Rob himself introducing his work.

The code, if you’re interested, is freely available online, and included here for your convenience.

echo "g(i,x,t,o){return((3&x&(i*((3&i>>16?\"BY}6YB6%\":\"Qj}6jQ6%\")[t%8]+51)>>o))<<4);};main(i,n,s){for(i=0;;i++)putchar(g(i,1,n=i>>14,12)+g(i,s=i>>17,n^i>>13,10)+g(i,s/3,n+((i>>11)%3),10)+g(i,s/5,8+n-((i>>10)%3),9));}"|gcc -xc -&&./a.out|aplay

The end result of running this tiny piece of code is a chiptune which sounds like this:

Pretty cool work, but as a project, this seems hard to extend.

BitShift Variations Unrolled

Enter James Newton, who is also fascinated with Rob’s code. He decided to unroll the code and express it in a longer, more human-readable way, to make it easier for others to understand.

James’s unrolled code is available on Github.

BitShift Variations: Lilypond Edition

A key limitation of the original BitShift Variations code is that it can only output a sound wave directly, and not any kind of score.

John Donovan re-implemented the algorithm from the original BitShift code in Python and gave it the ability to generate its output in Lilypond format, instead of a sound wave. Lilypond is a versatile music notation system, and from here the score of BitShift Variations in C Minor can be exported from Lilypond to various other formats.

John’s Python code is also available on Github and there is also a rendering of his MIDI output on SoundCloud:

BitShift Variations for Pipe Organ

I’ve long thought pipe organs are the original synthesizers, and have a lot in common with chiptune technology. You start with a fundamental tone (the basic organ flute pipe has a sound quite close to a pure sine wave) and create richness in the sound by adding in higher harmonics and then combining notes in harmony.

I’m also fortunate enough to have access to a real pipe organ which was renovated in 2020 and now has MIDI ports which can be used to record and play back music from a computer or other MIDI-enabled instrument.

So when I heard there was a Lilypond version of the BitShift Variations, there was no way I was not going to find a way of playing it back on the organ!

I cloned John Donovan’s BitShift Variations: Lilypond Edition and ran the following commands:

# Run the BitShift code to output the score in Lilypond format
python2.7 main.py > bitshift_variations.ly

# Use Lilypond to convert the Lilypond score to MIDI format
lilypond bitshift_variations.ly

I then imported this MIDI file into my favourite notation editor, MuseScore. BitShift Variations is written for 4 voices, which MuseScore natively interprets as 4 instruments. For this to work on an organ, I need to do a little bit of mapping.

Organs typically have two or more keyboards (manuals) and a pedalboard. The organ I’ll be using has two manuals and a pedalboard, so that can be thought of as 3 “voices”, although each voice is also capable of polyphony.

Taking BitShift Variations’ voices to be 1-4, starting with 1 as the lowest voice, I mapped voice 1 to the pedals, voices 2 and 3 to the Great organ (the lower of the two manuals) and voice 4 to the Swell organ (the upper manual). This is a fairly typical setup for classical music (although in this case, it probably isn’t possible to play 3 voices with 2 hands!).

Here’s my recording of BitShift Variations being played back on the organ. The video is a screen capture from an app called OrganAssist, which is specifically designed to control MIDI-enabled pipe organs. The sound is a recording of the actual sound – just air moving through pipes.

MuseScore has a really cool ecosystem for uploading and sharing scores, so they can be played back, downloaded and edited. So I’ve uploaded my arrangement of BitShift Variations for Pipe Organ for general consumption. Feel free to further edit it and see what you can come up with.