Many of the most expressive synths ever made are built around a modulation matrix, a grid where any source can control almost any destination. With the arrival of MPE-compatible emulations such as the new Oberheim Matrix-12 plugin from GForce and the growing set of expressive controllers, learning to wire gestures into a matrix is a skill worth having. This guide covers the principles, and they apply to any synth that offers MPE and a flexible matrix.
Know Your Three Gestures
MPE gives every note three independent streams of control, described in the MIDI Association specification:
- Pitch bend: horizontal movement, usually a glide or vibrato. Both sides must agree on the bend range, so set it to match.
- Pressure: how hard you press after the note starts, often called channel pressure in MPE.
- Slide: vertical movement, sent as CC74 on the note's own channel.
Add velocity and release velocity at the start and end of each note, and you have five dimensions to play with. A matrix lets you decide what each one does.
Step 1: Start With One Source and One Destination
Resist the urge to connect everything. Begin with pressure to filter cutoff. Play a held chord and push into one key at a time. If only that note brightens, your synth and controller are handling pressure per note. If the whole chord brightens, you are likely on a single channel or in a mode that is not MPE.
Step 2: Give Slide a Different Job
A common beginner mistake is to assign slide and pressure to the same destination, which makes gestures fight each other. Give slide something with a different character. Good candidates are filter resonance, oscillator mix, wavetable position or FM amount. Pressure usually works well for loudness, brightness or effect sends because it is a natural "lean in" gesture.
Step 3: Set Amounts Carefully
Most matrices let you set a depth for each connection. Keep depths modest at first, then increase them until the effect is musical rather than dramatic. A few rules of thumb:
- If a sound needs a very hard press to react, raise the depth or check your controller's pressure curve.
- If it reacts too quickly, lower the depth or smooth the source with a lag or slew processor, if the synth offers one.
- Use bipolar depths where available so that slide can move a parameter both up and down from a centre position.
Step 4: Layer Envelopes and LFOs With Gestures
Gestures do not replace envelopes. They sit on top of them. A pattern many players like is to let an envelope shape the basic filter movement while pressure adds extra brightness. Then use a slow LFO on pitch with the amount controlled by pressure, so vibrato appears only when you lean into the note. In a matrix, that is simply an LFO feeding pitch with pressure feeding the LFO's amount, if your synth allows modulating a modulation amount.
Step 5: Watch for Per-Note Versus Global Sources
Not every source in a matrix is per note. A mod wheel, a global macro or a master LFO may affect every voice at once. In a good MPE patch, the expressive parameters use per-note sources, while global parameters such as reverb size or delay feedback use global ones. If a patch sounds muddy when you play chords, check whether a gesture meant for one note is hitting all of them.
Step 6: Test With Real Playing, Not Just Single Notes
Test with chords, overlapping notes and fast runs. MPE lives in the interaction between voices. A patch that sounds great on a single note can feel unstable when four fingers move at once, particularly if voice stealing kicks in. Keep an eye on polyphony limits and your controller's channel count.
A Simple Starter Recipe
Try this on any subtractive or FM synth with a matrix:
- Set the synth's pitch bend range to match your controller (commonly 48 semitones for MPE zones, but check your manual).
- Route pressure to filter cutoff at a moderate depth.
- Route slide to resonance or FM amount at a lower depth.
- Route pitch glide to pitch, and add a touch of vibrato from an LFO whose depth rises with pressure.
- Save the patch and play it through a slow pad chord, then a fast melody.
Final Thoughts
A modulation matrix rewards patient experimentation. Start small, give each gesture a clear job and test with real musical phrases. The better you understand the three MPE dimensions, the easier it becomes to turn any matrix synth into an instrument that feels alive under your fingers.