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Notes and MIDI events

Notes and names

A common approach to composition in isobar-ext is building up patterns of notes, which correspond to the standard MIDI note range (0..127, with 60 = middle C) and velocity range (0..127).

timeline.schedule({
    "note": iso.PSequence([ 60, 64, 67, 72 ], 1),
    "amplitude": 64
})

To get a note from its string representation, use the note_name_to_midi_note utility function:

>>> print(iso.note_name_to_midi_note("G#2"))
32

Note events support the following properties:

property type description
note int MIDI note value
amplitude int MIDI note velocity
duration float Interval between notes (seconds)
gate float Proportion of note to sustain (where 1.0 = legato)
key Key Key for degree lookup
scale Scale Scale for degree lookup
degree int Degree within key/scale (cannot be used if note is specified)
transpose int MIDI note transpose
octave int MIDI note octave transpose
active int If false, skips the note

Duration and gate

The duration specifies the interval between one note and the next. The gate key specifies what proportion of this interval the note will be sustained for (and defaults to 1.0, for seamless legato).

For instance:

#--------------------------------------------------------------------------------
# Play a note every beat, sustained for half a beat
#--------------------------------------------------------------------------------
timeline.schedule({
    "note": 60
    "duration": 1,
    "gate": 0.5
})

The gate can also be greater than 1, to hold a note down as the next note begins:

#--------------------------------------------------------------------------------
# Play a sustained, overlapping chord, with each note lasting for 4 beats
#--------------------------------------------------------------------------------
timeline.schedule({
    "note": iso.PSequence([ 60, 64, 67, 72 ], 1),
    "duration": 0.5,
    "gate": 8
})

Keys and Scales

isobar has builtin objects representing musical keys and scales.

  • Scale encapsulates an ordered set of semitones. Named scales are defined corresponding to commonly-used scales (major, minor, chromatic, aeolian, etc).
  • Key encapsulates a Scale with a specified tonic.

Warning

isobar currently only supports equal temperament tuning.

Keys and scales can be used in events by using the degree key to look up a specific degree within the key/scale. transpose and octave can be used to transpose by semitones and octaves respectively. 

#--------------------------------------------------------------------------------
# Play an F minor arpeggio
#--------------------------------------------------------------------------------
timeline.schedule({
    "degree": iso.PSequence([ 0, 2, 4, 7 ], 1),
    "key": iso.Key("F", "minor"),
    "octave": 4
})

Chords

Chords can be specified by passing tuples of notes to the note or degree property.

#--------------------------------------------------------------------------------
# Play a series of 3-note chords.
#--------------------------------------------------------------------------------
timeline.schedule({
    "degree": iso.PSequence([
        (0, 1, 4),
        (1, 4, 6),
        (3, 4, 7),
        (-1, 0, 4),
    ]),
    "octave": 4,
    "duration": 2
})

You can also specify different amplitudes or gates for notes of a chord by passing tuples of the same length:

timeline.schedule({
    "note": iso.PSequence([
        (60, 62, 67),
    ]),
    "gate": iso.PSequence([
        (0.25, 0.5, 1)
    ]),
    "amplitude": iso.PSequence([
        (96, 64, 32),
        (64, 96, 32),
        (64, 32, 96),
    ]),
    "duration": 0.25
})

Rests

Use None to specify a rest:

timeline.schedule({
    "note": iso.PSequence([ 60, 60, None, 60, None, 60, 60, None ]),
    "duration": 0.25
})

Many Pattern classes can operate explicitly on rests, or introduce rests.

For example:

  • PCollapse takes an input and steps past any rests to remove gaps
  • PSkipIf replaces notes with rests given a conditional
  • PSkip replaces notes with rests randomly given a probability
  • PPad pads a sequence with rests until it reaches a specified length