Sonic Pi metre and micro-timing

This is a Ruby gem for Sonic Pi which adds functionality for musical metre and probabilistic micro-timing. This is an alternative way of playing music to using Sonic Pi's typical play and sleep commands. The implementation of metre has been designed to be very generalisable to allow almost any metrical hierarchy to be represented.

For more details about this project and its implementation, see the bibliography. The Ruby gem can be found on RubyGems.

Installation

If you installed Sonic Pi from the official installer, you can install this gem by running the following command (as an administrator):

<SONIC-PI-INSTALL-DIR>/app/server/native/ruby/bin/gem install sonicpi-metre

Or if you've built Sonic Pi from source using your system's installation of Ruby:

gem install sonicpi-metre

Usage

After installation, you can use the library in a Sonic Pi project:

require 'sonicpi/metre'

A simple example of how to play music in this metrical framework is shown below. See the documentation below for more details.

use_metre '4/4'
bar do
  add_note :C4, 1, 1 # Plays the C4 note for one quaver/eighth note
  add_note :D4, 0, 3 # Plays the D4 note for three crotchets/quarter notes
  add_note :E4, 2, 1
  add_note :C4, 2, 1
end

The second part of this project was to add style-specific probabilistic micro-timing (like those found in swing rhythms or Viennese waltz music). We define a probability distribution for each metric event and use time_warp to adjust the timing of notes played on those events.

To use this, the desired style is passed as an optional second argument to use_metre or with_metre. E.g.:

use_metre '3/4', :viennese_waltz

Documentation

use_metre <metre> [style]

Sets the metre to be used for the current thread.

A metre can be defined as a time signature string or a nested list of Rationals. The style argument specifies a micro-timing style to apply to music played in this metre.

Examples:

use_metre '4/4' # This uses a preset metre represented by a 4/4 time signature

use_metre [[1/8r,1/8r,1/8r], [1/8r,1/8r,1/8r]] # This creates a metre with two beats, each of which can be divided into three eighth notes (the 6/8 time signature)

use_metre '3/4', :viennese_waltz # Uses the micro-timing of the Viennese Waltz style. You should notice the second beat of each bar falls slightly early. Note that the style has to be compatible with the metre.

Supported time signatures:

'2/4'
'3/4'
'4/4'
'6/8'
'9/8'
'12/8'

Supported style presets:

:viennese_waltz # Second beat is slightly early. Typically uses a 3/4 time signature
:jembe # Micro-timing of jembe music from Mali. Typically uses a 12/8 time signature
:triplet_swing # Jazz swing. Typically uses a 4/4 time signature

with_metre <metre> [style] <block>

Uses the given metre for the block. See use_metre for details.

bar <block>

Creates a new bar in the current metre.

All notes played with add_note inside the block argument will belong to this bar. You cannot add more notes than will fit into the bar's total duration. Bars cannot be nested. If all the notes in a bar don't fill its duration, then the bar automatically sleeps for the remaining time.

Example:

use_metre '4/4'
bar do
  add_note :C4, 1, 1 # Both notes are part of this bar
  add_note :D4, 0, 3
  # The bar automatically sleeps for the remaining 3 eighth notes
end

add_note <note> [level=0] [duration=1]

Plays a given note for a specified duration as part of the current bar on the current synthesizer.

level specifies the metrical level the note should exist at, as defined by the current metre. Level 0 is the beat level. Levels 1, 2, etc. are division levels (e.g. quarter notes, eighth notes, etc.). Levels -1, -2, etc. are multiple levels (e.g. half notes, whole notes, etc.). duration specifies how many of these notes it should last for. This method must be called from within a bar block.

The timing of the note will be shifted according to any micro-timing set in the current metre. Additional arguments will be passed to the internal call to play.

Example:

use_metre '4/4'
bar do
  add_note :C4, 1, 1 # Plays the C4 note for one quaver/eighth note
  add_note :D4, 0, 3 # Plays the D4 note for three crotchet/quarter notes
end

There are also shorthand functions which wrap calls to add_note. They assume simple metre for the beat level and above (<= 0), and assume simple or compound metre for division levels (> 0). These are listed below:

add_whole
add_half_d # Dotted half note
add_half
add_quarter_d
add_quarter
add_8th_d
add_8th
add_16th

# British names
add_semibreve
add_minim_d
add_minim
add_crotchet_d
add_crotchet
add_quaver_d
add_quaver
add_semiquaver

add_sample <sample_name> [level=0] [duration=1]

Same as add_note but will play a sample using Sonic Pi's sample command.

add_rest [level=0] [duration=1]

Adds a rest (a period of silence) of the specified length.

Bibilography

Full details can be found in the paper:

M. Johnson and M. Gotham, “Musical Micro-Timing for Live Coding”, in Proc. of the 24th Int. Society for Music Information Retrieval Conf., Milan, Italy, 2023. https://archives.ismir.net/ismir2023/paper/000010.pdf

The code used to derive the micro-timing found in the preset Styles can be found here.