Walking Bass

This script implements a walking bass line. It uses a random number generator combined with knowledge of the chord progression to create a unique line for each measure.

The script makes use of the Calf FluidSynth LV2 plugin, the configuration for this plugin is defined in a separate class included here via the import statement:


import "fluidsynth.bip"

Define the class and member data:

a FluidSynth Object loaded with patch 32 ("Acoustic Bass")
a random number generator


class WalkingBass {

  bass = FluidSynth(32)
  rand = Math.Random()

Choosing Notes

Define a function to choose a random note from the given chord, loop until the note is a different pitch than the last note to avoid repeats.


  function chordNote(chord, last, velocity) {
    local chosen = last
    while(chosen.pitch == last.pitch) {
      local index = rand.integer(chord.len())
      chosen = chord[index].note
    }
    return Midi.Note(chosen.pitch, velocity, 0.25)
  }

Define a function to choose a leading note into the next chord.


  function leadingNote(next, last, velocity) {
    local root = next[0].note.pitch

Loop until the chosen pitch is different than that of the last note.


    local pitch = last.pitch
    while(pitch == last.pitch) {

Choose an option for leading note at random:


      switch(rand.integer(6)) {

Pitches a half step above or below the next root:


        case 0:
          pitch = root + 1
          break
        case 1:
          pitch = root - 1
          break

Pitches a full step above or below the next root:


        case 2:
          pitch = root + 2
          break
        case 3:
          pitch = root - 2
          break

Pitches a perfect fifth above or below the next root:


        case 4:
          pitch = root + 7
          break
        case 5:
          pitch = root - 5
          break
      }
    }

Create and return a MIDI note from the chosen pitch:


    return Midi.Note(pitch, velocity, 0.25)
  }

Scheduling

Define the main method to schedule a measure of bass. This method takes four arguments:

the number of the measure
a "power" level between 0 - 100
the current chord in the progression
the next chord in the progression


  function schedule(measure, power, chord, next) {

The chords as passed in are centered around middle C, transpose them two octaves lower so they contain bass notes.


    chord = chord.transpose(-24)
    next = next.transpose(-24)

Calculate a velocity level based on the incoming power level, play the bass notes harder when the power is high and softer for lower power values:


    local velocity = 64 + power / 2

Schedule the root note of the chord as the first quarter note in the measure.


    local rootNote = chord[0].note
    bass.schedule(Midi.Note(rootNote.pitch, velocity, 0.25), measure)

Schedule chord notes as the second and third quarter notes in the measure.


    local note2 = chordNote(chord, rootNote, velocity)
    bass.schedule(note2, measure + 0.25)

    local note3 = chordNote(chord, note2, velocity)
    bass.schedule(note3, measure + 0.5)

Schedule a leading note to the next chord as the last quarter note in the measure.


    local note4 = leadingNote(next, note3, velocity)
    bass.schedule(note4, measure + 0.75)
  }

Audio Output

A simple function to return an Audio.Source which allows the class to connect to a mixer etc.


  function output() { return bass }

End of the class. See the main script for an example of using this class.

Complete Script

import "fluidsynth.bip"

class WalkingBass {

  bass = FluidSynth(32)
  rand = Math.Random()

  function chordNote(chord, last, velocity) {
    local chosen = last
    while(chosen.pitch == last.pitch) {
      local index = rand.integer(chord.len())
      chosen = chord[index].note
    }
    return Midi.Note(chosen.pitch, velocity, 0.25)
  }

  function leadingNote(next, last, velocity) {
    local root = next[0].note.pitch

    local pitch = last.pitch
    while(pitch == last.pitch) {

      switch(rand.integer(6)) {

        case 0:
          pitch = root + 1
          break
        case 1:
          pitch = root - 1
          break

        case 2:
          pitch = root + 2
          break
        case 3:
          pitch = root - 2
          break

        case 4:
          pitch = root + 7
          break
        case 5:
          pitch = root - 5
          break
      }
    }

    return Midi.Note(pitch, velocity, 0.25)
  }

  function schedule(measure, power, chord, next) {

    chord = chord.transpose(-24)
    next = next.transpose(-24)

    local velocity = 64 + power / 2

    local rootNote = chord[0].note
    bass.schedule(Midi.Note(rootNote.pitch, velocity, 0.25), measure)

    local note2 = chordNote(chord, rootNote, velocity)
    bass.schedule(note2, measure + 0.25)

    local note3 = chordNote(chord, note2, velocity)
    bass.schedule(note3, measure + 0.5)

    local note4 = leadingNote(next, note3, velocity)
    bass.schedule(note4, measure + 0.75)
  }

  function output() { return bass }

}

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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.