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MIDI Polyphonic Expression In Digital Performer

MOTU Digital Performer Tips & Techniques By Marty Cutler
Published October 2022

Screen 1: MPE allows modulation data to be applied to individual notes within a performance, rather than simply across the whole MIDI channel.Screen 1: MPE allows modulation data to be applied to individual notes within a performance, rather than simply across the whole MIDI channel.

We dive into DP’s extensive MPE capabilities.

This month, we delve into Digital Performer’s extensive MIDI Polyphonic Expression (MPE) features, which allow you to add increased expression and nuance in your MIDI performances and tracks. But first, what exactly is MPE?

I’ve always believed that MIDI guitar is a more naturally expressive controller than the average synthesizer keyboard controller. Set up properly, natural pitch bending and vibrato, for instance, are quite literally at the tips of your fingers. Each note’s pitch and timbre can vary and change in intensity, just as it does acoustically on a guitar or other stringed instrument. Until recent years, keyboards (and MIDI) have lagged behind in those more tactile modes of expression because, in MIDI 1.0, pitch bend, modulation and other continuous controllers (CCs) affect every voice (note) on a single MIDI channel equally. Very few conventional keyboards and synthesizers can modulate the pitch of a single note within a chord while leaving the other notes intact. MIDI guitars, on the other hand, have managed to accomplish this by routing the MIDI output of each string to a separate MIDI channel. In that way, each synthesizer voice can respond independently to MIDI messages.

MIDI Polyphonic Expression (MPE) takes MIDI guitar’s multi‑channel concept and runs with it, by way of redesigned keyboard controllers which can send discrete messages for each key, generated by multiple gestures. In addition to standard keyboard parameters such as velocity, release velocity and keyboard pressure (aftertouch), MPE devices sense motion on a key’s vertical and horizontal axes. Essentially, MPE assigns discrete streams of CC data to each note (Screen 1).

MPE rotates successive MIDI notes over 15 MIDI channels, with each note carrying its own MPE data. Similarly, every note you play on an acoustic instrument is a unique combination of articulations. Vibrato, timbre, string‑release noise, fret squeaks and breath (when playing a wind instrument), whether consciously executed or not, are all elements that can bring a sound to life. MIDI and, more extensively, MPE can translate and encode these musical dimensions into data that you can use to sculpt performances. Best of all, as with playing an acoustic instrument, the expression is under your fingertips. Still, as the great guitarist Lonnie Johnson once wrote: “To do this you gotta know how.”

Tools Of The Trade

Now let’s take a look at how you can make MPE work for you in Digital Performer. For starters, you’ll need three things: DP version 11.0x or later, an MPE‑capable controller, and an MPE‑ready synth, either hardware or virtual. Luckily, DP 11’s included synths support MPE.

So how about MPE‑capable controllers? Some follow a piano/keyboard paradigm, such as the ROLI Seaboard and the McMillen K‑Board Pro, while others, such as the Linnstrument, are more like freely configurable touchpads. As I write this, ROLI are preparing to introduce an updated version of the Seaboard. The main features to look for are velocity (of course!), pressure (both channel and polyphonic), X‑ and Y‑axis controls, and release velocity.

X & Y

Let’s review the keyboard gestures that comprise an MPE patch. Velocity is already a per‑note message in MIDI 1.0, and typically this controls both loudness and timbre. It can also switch or crossfade between samples, and as with most MIDI messages, velocity can be remapped to almost any parameter. MPE also supports release velocity, a measurement of how rapidly you let go of a key; typically, this affects the release time of a note’s envelope, but again, it can control other responses, such as triggering another sound.

Screen 2: Setting up Modulo to respond to an MPE controller.Screen 2: Setting up Modulo to respond to an MPE controller.The X‑ and Y‑axis controls arguably produce the most dramatic effects. By default, X‑axis movement generates pitch bends independently for each note. This is particularly useful in animating ensemble sounds. For instance, consider a live string ensemble: no two players will play with precisely the same intensity of vibrato. Because pitch bend is independent, it’s a great tool for instruments with contrary motion, such as pedal steel guitar. The Y‑axis is generally mapped to timbre, which often means modulating the filter cutoff frequency, but timbre can be animated in a number of ways.

MPE Setup In DP

Let’s start by setting up a track with DP’s Modulo: a two‑oscillator, subtractive wavetable synth. From DP’s Project menu, go to Add Track / Instrument Track / MOTU / Modulo (stereo). The resulting instrument track must be set to handle incoming MPE data. From the track’s settings menu, choose Open Protocol Settings. For input, choose your MPE controller from the menu and choose MPE from the Record Protocol menu. For Output, choose MPE from the Playback Protocol menu (Screen 2).

Make sure your controller is set to transmit MPE data. Most MPE‑capable controllers default to MPE, but they are often switchable between a variety of modes including traditional single‑channel MIDI. I usually keep the control panel loaded in the background so I can change parameters as needed: for example, I may need to tame the pitch‑bend response of my ROLI Seaboard to keep things more or less in tune (Screen 3).

Screen 3: Many MPE controllers ship with a piece of control software that lets you alter how they respond to your physical input.Screen 3: Many MPE controllers ship with a piece of control software that lets you alter how they respond to your physical input.

Check It Out

Maybe the most dramatic MPE feature is the Glide function. If you have a ROLI Seaboard, try this: load a sustaining patch in Modulo and, while holding down a chord (any chord!), strike a new note, and glide it to a higher pitch from below the chord. If things are set up properly, your second note will sweep to the new pitch, while the chord remains unchanged. Other keyboards, such as the Keith McMillen K‑Board Pro, will trigger all notes in the glide and quantise them to the nearest pitch, as if you were performing a gliss on a piano; however, you can add separate vibrato by holding down a chord and wiggling the new note, as if you were adding vibrato to a guitar string. Notice the vibrato effect and how the chord remains stable; try doing that with an ordinary pitch or mod wheel!

Vibrato, timbre, string‑release noise, fret squeaks and breath, whether consciously executed or not, are all elements that can bring a sound to life.

Party In Another Dimension

For now, let’s explore the Slide dimension. As yet, MOTU are still working on implementing Slide (CC 74) in DP’s included synth plug‑ins for a future update. If you have third‑party MPE synths, you’ll want to fire one up and try it. If you own a Seaboard, it is bundled with several MPE‑capable synths, including Equator 2. Rhizomatic Software Plasmonic is one of my favorites for its unique sounds. Arturia Pigments is another synth with a fine collection of MPE sounds, and UVI Falcon has a generous folder full of killer MPE patches. Follow the same procedure for instantiating a third‑party MPE synth, choose an MPE patch, and slide your finger up and down the key, noticing a change in timbre. Hold a chord and add a new note, observing individual changes in timbre. Usually, it’s the filter, opening and closing, but if you keep your eye on the synth’s UI, you’ll notice some control or graphic element moving in time with your slide. It might be some other element that changes, such as pulse width, symmetry, a wavetable sweep, or some other specialised feature of the instrument.

Now that you know a little about the way MPE works in Digital Performer, what can you do with it? In our next DP workshop, we will look at a few creative options: tricks, tips, and other cool ideas for making MPE a creative vehicle within Digital Performer. For instance, there is a pretty simple way you can set up the K‑Board to perform large‑scale pitch swoops, and a few other tricks not so easily accomplished by the Seaboard or other similar devices.

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