Polyrhythmix

Polyrhythmix (Poly) is a command-line assistant designed to generate MIDI files from the description of drum parts. It provides a convenient way to input a DSL (Domain-Specific Language) in the command line, then it calculates when the drum parts will converge together, making it easy to compose polyrhythmic parts with frequent shifts over the bar lines. Additionally, it can generate a bass MIDI track that follows the kick drum.

Polyrhythmix is specifically designed to assist musicians and composers working in genres such as modern progressive rock, metal, djent, fusion, and Indian Carnatic music. It aims to simplify the process of creating complex polyrhythmic drum patterns, enabling users to focus on the creative aspects of their compositions.

Motivation

I'm a guitar player, and I use tablature notation editors such as Guitar Pro a lot. However, it gets complicated fast when I write polyrhythmic/polymetric drum parts, because shifts tend to go over the bar lines and it's hard to make sense it's correct visually (may be even harder if you listen to it). The other property of such parts is: it tends to unfold from simple ideas such as "I want to create a drum part that will have a 3 against 4 feel with a kick drum against a snare drum". The other way to think about it is that it has a simple blueprint, but it's tricky and error-prone to express in Western musical notation. This is why Polyrhythmix exists. I wanted to have a simple tool to workshop/brainstorm rhythmic ideas and evaluate them by having a MIDI playback. I'm into modern Progressive Rock/Metal music, Fusion, so it all applies very well. I have an impression it may be useful for Indian Carnatic music as well, but I would like to get some insightful confirmation on that.

Features

Drum Generation: Polyrhythmix takes a DSL input to define polyrhythmic patterns for various drum instruments. It intelligently calculates when different drum parts will converge, ensuring rhythmic synchronization.

MIDI File Generation: Once the polyrhythmic pattern is defined, Polyrhythmix generates a MIDI file containing the drum parts. This file can be imported into any compatible software or hardware for further editing or playback.

Bass Track Generation: Polyrhythmix offers an option to generate a bass MIDI track that follows the kick drum. This feature provides a foundation for creating cohesive rhythm sections by synchronizing the bassline with the kick drum pattern.

Installation

For Rust developers (or other people who have cargo on their machine):

cargo install polyrhythmix

Usage

Polyrhythmix runs as an executable with the desired command line options. The available options are as follows:

Usage: poly [OPTIONS]

Options:
  -K, --kick <KICK>
          Kick drum pattern
  -S, --snare <SNARE>
          Snare drum pattern
  -H, --hi-hat <HIHAT>
          Hi-Hat pattern
  -C, --crash <CRASH>
          Crash cymbal pattern
  -t, --tempo <TEMPO>
          Tempo value [default: 120]
  -s, --time-signature <TIME_SIGNATURE>
          Time signature [default: 4/4]
  -o, --output-file <OUTPUT>
          Output file path, make a dry run if omitted
  -B, --follow-kick-drum-with-bass
          Generate a second MIDI track for the bass following the kick drum
  -h, --help
          Print help
  -V, --version
          Print version

Polyrhythmix uses a simple DSL (Domain-specific language) for drum patterns. For a more detailed explanation, go to DSL Overview.

Let's say you want to tell if two patterns will converge and how soon. We'll start with a 3 against 4. The first pattern would be a series of 8th notes on the kick drum

poly  --kick '8x--x--' --snare '4-x'

Output

No output file path was supplied, running a dry run...
Converges over 3 bars

We haven't provided an --output-file / -o parameter, so poly made a dry run. It tells us it will converge in 3 bars. Let's see how it will look in the MIDI file by adding an output.

poly  --kick '8x--x--' --snare '4-x' -o out.mid

Output

Converges over 3 bars
out.mid was written successfully

Polyrhythmix operates under the assumption that it's easy to replicate a fully converged pattern in the DAW or tablature editor, so it only generates 3 bars of drums in this case. On Mac OS, I usually do something in lines of poly <OPTIONS> -o out.mid && open out.mid or poly <OPTIONS> -o out.mid && open -a 'Guitar Pro 7' out.mid.

This way it defaults to 4/4 as a time signature, but we may want to interpret this rhythmic pattern in 3/4 for example. Let's try it:

poly --time-signature '3/4' --kick '8x--x--' --snare '4-x' -o out.mid && open -a 'Guitar Pro 7' out.mid

Output:

Converges over 2 bars
out.mid was written successfully

Now we can see it converges in 2 bars, not 3. Honestly, I like the 4/4 host time signature better. Let's get back to it. Also, we can add a crash cymbal and hi-hat patterns too, also we can make it just a bit livelier by increasing the tempo:

poly --time-signature '4/4' --tempo 138 --crash '4x---' --hi-hat '8-xxx' --kick '8x--x--' --snare '4-x' -o out.mid

That's cool, but let's make it even more useful by adding a blueprint for the bass track. Simple way of doing that is to make bass follow the kick drum. Poly has an option to do this called -B/--follow-kick-drum-with-bass. Let's add it to the previous command to add the bass track to the output file:

poly --time-signature '4/4' --tempo 138 --crash '4x---' --hi-hat '8.t-xxx' --kick '8x--x--' --snare '4-x' -o out.mid -B

Now we have two tracks in the output file and you can change the bass notes to create an expected harmonic context.

Let's try one more thing:

poly -t 115 -K '32xx16xx' -H '8x' -S '4--x-' -B -o bleed.mid

Congratulations, now you have a basic version of "Bleed" by Meshuggah!

To get to the next level, you need to understand that note groups can be recursive if you nest them. For example (3,8x(3,16x-xx(3,32xx-x)))) would read as "Three repeats of an eighth note hit, then three nested repeats of hit, rest, hit, hit in sixteenth notes, then three repeats of hit, hit, rest, hit in thirty-second notes". It sure is a mouthful, but the point is: any repeat of a nested child group would be applied to every repeat of the parent group that includes it.

DSL overview

Any pattern can be described by a series of note groups. All notes in the note group have the same length. Possible lengths are:

• 1 - Whole note
• 2 - Half note
• 4 - Fourth note
• 8 - Eighth note
• 16 - Sixteenth note
• 32 - Thirty-second note
• 64 - Sixty-Fourth note
• . - dotted note (meaning it has 1.5 lengths of unmodified duration). Dot should be applied after the basic length like this: 8.
• t - Triplet notes, should be applied after basic lengths and dots. e.g. 4.t means triplets of dotted fourth notes.

Now let's talk about the drums. Poly has a logic similar to a drum machine, so we only concern ourselves with drum hits and rests:

• x - Hit
• - - Rest

Let's compose a few simple note groups:

• 4x - a group of a single fourth note.
• 8.-x a group of a rest and a drum hit. Both rest and hit have a length of 8th dotted note each.

It's possible to repeat a group of notes of the same length with the following syntax:

• (3,8x-x) means repeat three times a series of hit, rest, hit in eighth notes

Now that we know that, we may sequence multiple groups like this:

• 32xx16xx - Kick pattern from "Bleed" by Meshuggah

Note groups can be nested within each other, which interacts in interesting ways with repeats:

• (3,16x(3,8txxx(3,32x-x-x-))) I'm struggling to make a compelling example, so here's a triple-nested pattern that converges over 471 bars of 4/4

Guitar pro remarks

Don't forget to quantize MIDI imports to 64th notes as it gets increasingly crazier as we get into the wilder note groupings:

Contributing

Contributions are very welcome, feel free to open issues, open pull requests, and give me feedback regarding this piece of software.

Contact

If you encounter issues or have questions about using Poly, please feel free to reach out to me via email.