Poly Aftertouch: Ready for Prime Time

One of the complaints about electronic music instruments and controllers is that they lack the expressiveness of acoustic instruments. Although future instruments will take advantage of MIDI 2.0's enhanced expressiveness, two options are available right now: polyphonic pressure, and MPE (MIDI Polyphonic Expression). Studio One 5 can record/edit both, and ATOM SQ generates polyphonic pressure so let's dig deeper.

Language Lesson First, there's some confusion because people call the same function by different names. Channel Aftertouch = Channel Pressure = Mono Aftertouch = Mono Pressure. Polyphonic Aftertouch = Polyphonic Pressure = Poly AT = Poly Aftertouch = Poly Pressure. Okay! Now we've cleared that up.

Aftertouch: Two Flavors Aftertouch generates a control signal when you press down on a keyboard key after it's down, or continue pressing on a percussion pad after striking it. Aftertouch is a variable message, like a mod wheel or footpedal-not a switch. A typical application would be changing filter cutoff, adding modulation, or doing guitar-like pitch bends by pressing on a key.

There are two aftertouch flavors. Mono pressure has been around since the days of the Yamaha DX7, and sends the highest controller value of all keys that are currently being pressed. Polyphonic pressure sends individual pressure messages for each key. For example, when holding down a chord for a brass section, by assigning poly pressure to filter cutoff, you can make just one note brighter by pressing down on its associated key. The other chord notes remain unaffected unless they're also pressed.

Controllers with polyphonic aftertouch used to be fairly expensive and rare, but that's changing-as evidenced by ATOM SQ.

Synth Requirements As expected, you need a synth that responds to poly pressure. Many hardware synths respond to it, even if they don't generate it. As to soft synths, although I haven't tested all of the following, they reportedly support poly pressure: several Korg Collection synths, Kontakt, Reaktor, all Arturia instruments, all U-He instruments, XILS-Lab synths, TAL-Sampler, AAS synths, Albino 3, impOSCar2, Mach5, and Omnisphere. If you know of others, feel free to mention them in the comments section below. (Currently, Studio One's bundled instruments don't respond to polyphonic aftertouch.)

The Controller Figure 1: ATOM SQ being set up to generate Poly Pressure messages.

With ATOM SQ, press the Setup button. Hit the lower-left pressure button below the display, then spin the dial to choose Poly (Fig. 1). Note that if ATOM SQ outputs poly pressure, most instruments that respond only to channel (mono) aftertouch will ignore these messages.

Recording and Editing Record poly pressure in Studio One 5 as you would any MIDI controller. To edit pressure messages, use the Edit window's Note Controller tab. Select Pressure for the Type, and then the Pitch of the note you want to edit. Or, click on a note to select its corresponding note Pitch automatically. You can then edit that note's poly pressure controller as you would any other controller (Fig. 2).

Figure 2: The selected Note's data is white; unselected notes of the same pitch are blue. The gray lines in the background show the poly pressure controller messages for notes with other pitches.

It may seem that editing data for individual notes would be tedious, and it can be. However, because poly pressure allows for more expressive real-time playing, you might not feel the need to do as much editing anyway-you won't need to use editing to add expressiveness that you couldn't add while playing.

A fine point is that it's currently not possible to copy Note Controller data from one note, then paste it to a note of a different pitch (probably because the whole point of poly AT is for different notes to have different controller data). However, if you copy the note itself to a different pitch, the Note Controller data will go along with it.

Although ATOM SQ can adopt a layout that resembles a keyboard, it would be a mistake to see it as a stripped-down version of a standard keyboard. Controllers with polyphonic pressure tend to think outside the usual keyboard box, by incorporating pads or other transducers that are designed for predictable pressure sensitivity. Poly pressure has been around for a while, but a new generation of MIDI controllers (like ATOM SQ) are making the technology-and the resulting expressiveness-far more accessible for those who want to wring more soul out of their synths.

LINK:	https://blog.presonus.com/index.php/2020/11/20/poly-aftertouch-ready-p...
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