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Microtonal pitch modulation using the step sequencer

Jacky Ligon edited this page Jul 27, 2020 · 13 revisions

Microtonal Step Sequencing

In addition to the standard Step Sequencer functions outlined in the manual, enhancements in Surge 1.7 enable using it for quantizing the pitch of sequencer steps to degrees of loaded Scala SCL microtuning table files.


Modulating Scene Pitch vs. Oscillator Pitch

An initial consideration in configuring Step Sequencers for microtonal sequencing is that there are actually two possible Pitch Modulation targets to which Step Sequencer modulation-sources may be assigned:

Scene Pitch

Modulating Scene Pitch with one, or multiple, Step Sequencers is useful where one wants all three oscillators in a Scene to track the pitch in unison. With Scene Pitch modulation using more than one Step Sequencer, all of the modulation sources are summed to a single voice. Polyphonic input from a MIDI controller is still possible, but each voice contains the sum of all running Step Sequencers assigned to Scene Pitch.

Oscillator Pitch

With Oscillator Pitch modulation using the Step Sequencers, it is possible to route separate sequencers to each of the three available oscillators in a Scene. In this scenario, it becomes possible for the sequencers to trigger chords as the notes from each Step Sequencer play together.





Making Step Sequencer Modulation Assignments for Microtonal Sequencing

Since the processes for routing Step Sequencer modulation-sources to either Scene Pitch or Oscillator Pitch are functionally identical, in this brief overview, we’ll focus on assigning Step Sequencers to Oscillator Pitch for microtonal pitch sequencing:

  1. Load a Scala SCL microtuning table file to use with the Step Sequencer, as outlined in the Microtonal Tuning section of the user manual. For this example, we’ll use 15-tone-equal-temperament, which is available in the factory data tuning-library as ED2-15 (Equal division of harmonic 2 into 15 parts).

  2. Right-Click on the Oscillator Pitch slider, and check Extend Range in the context menu. Doing this enables pitch sequencing with SCL microtonal tuning tables of arbitrary size.



  1. Assign a SEQ modulation-source to the Oscillator Pitch. For more info on assigning modulation sources to targets, read this section in the manual.

In the Modulation Routing Section, add a SEQ to a modulation slot, click on it, which turns its button green, placing it in modulation-routing mode. Next, drag the Oscillator Pitch slider to the right, then right-click on the slider and type-in a value of 15, which sets the Edit SEQ → Pitch +/- Keys range to the size of our loaded SCL microtuning table file. Here, it is also possible to type-in a range of 30 (in this case, twice the loaded SCL scale size) for creating microtonal pitch-sequences over a range of two times the repetition interval (the interval at which any scale repeats across the range), which we’ll cover in more detail below.




  1. With these settings configured, the Surge Step Sequencers become ‘SCL-aware’, and now we are ready to create our microtonal Step Sequencer patterns. In the Step Sequencer Editor, place the mouse cursor over one of the 16 steps, hold Shift, then drag up or down to create a pitch-quantized step over the range of one repetition interval. Here, one will notice that a popup appears, showing the pitch-quantized adjustments as they snap to degrees of the loaded SCL file when one drags the mouse up and down.


  1. It is also possible to draw straight-lines across multiple steps in the Step Sequencer Editor and quantize their pitches to degrees of the loaded SCL microtuning table file, using the Right-Mouse-Button in combination with the Shift+Drag and Alt+Shift+Drag mouse-modifiers.


Step Sequencer Mouse Modifiers Reference

Use the below keyboard modifiers to create sequencer steps that are quantized to the pitch of the loaded SCL microtuning table file:

  • Shift+Drag for quantizing vertical sequencer-editor steps to scale degrees spanning a range of one repetition interval (2/1, 3/1, 4/1, etc.).
  • Alt+Shift+Drag for quantizing vertical sequencer-editor steps to scale degrees spanning a range of twice the repetition interval.
  • Shift+Right-Mouse-Button+Drag for drawing straight-lines across multiple steps in the sequencer-editor that quantize to scale degrees spanning a range of one repetition interval.
  • Alt+Shift+Right-Mouse-Button+Drag for drawing straight-lines across multiple steps in the sequencer-editor that quantize to scale degrees spanning a range of twice the repetition interval.
  • Double-Click to clear individual sequencer steps, or Ctrl+Drag across a range of steps to clear them.

Use the Alt+Shift+Drag and Alt+Shift+Right-Mouse-Button+Drag mouse-modifiers when setting the pitch-range to twice the SCL size, as detailed in step-3 above. Doing this effectively doubles the number of vertical steps in the sequencer-editor.




Note: Without any keyboard-modifiers, the pitch is not quantized to the loaded SCL file and essentially functions as a stepped modulation-source similar to an LFO.