What Is Aftertouch? Channel vs Polyphonic Explained
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What is aftertouch? It is changing pressure data produced when you press farther into a held key after the initial strike. Channel aftertouch affects the whole MIDI channel, while polyphonic aftertouch can control each held note separately.
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What is aftertouch, and how is it different from velocity?
Velocity records how hard or fast you first strike a key, while aftertouch changes as you continue pressing it. Aftertouch is control data rather than an effect, so the receiving patch decides whether it adds vibrato, opens a filter or raises the volume. Channel Pressure, also called channel or mono aftertouch, sends one value that usually affects every held note. Polyphonic Key Pressure includes the note number, so pressing the top note of a chord can brighten that note without changing the others.
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How do you use channel and polyphonic aftertouch?
Choose Channel Pressure, Mono Aftertouch or Poly Aftertouch as a source in the synth’s modulation matrix. Map it to filter cutoff, volume, LFO depth for vibrato or an effect level, then add a small modulation amount. Test it by holding a chord and pressing one key harder while watching a MIDI monitor. The controller, DAW and instrument must all pass the same message type, or the response may disappear or be reduced to one shared value.
The ASM Hydrasynth Keyboard sends polyphonic aftertouch, although its engine can also receive channel aftertouch when a patch uses `MonoAftT` instead of `PolyAftT`. Expressive E Osmose can switch between channel and polyphonic aftertouch configurations, while adding deeper pressure and sideways key movement for MPE control. Polyphonic aftertouch is not the same as MPE because MPE can also carry per-note pitch bend and timbre over separate member channels. Our Expressive E Osmose CE 61 review covers how that more expressive key action feels in practice.
Among the recent controller previews, the Behringer POLYKEYS 61 stands out because it is expected to offer polyphonic aftertouch. That could make it a popular option when it is released, especially for players who want per-note pressure control without moving to a Hydrasynth or Osmose. Behringer has not yet published a full official product page, final specifications or a shipping date, so it is still too early to treat it as a current alternative.
Our Everything You Need to Know About the Expressive E Osmose CE 61 review shows the keyboard’s expressive controls in use and explains how they affect playing in practice.
Everything You Need to Know About the Expressive E Osmose CE 61 | Review
Our verdict
Channel aftertouch handles chord-wide expression well, while polyphonic aftertouch is worth having when you want to shape individual notes.
Pros
Expression without another controller
Natural vibrato and filter control
Per-note response with poly aftertouch
Cons
Needs support throughout the MIDI chain
Some presets require manual mapping
Keybed response varies between models
Which type of aftertouch should you choose?
Channel aftertouch is enough for chord-wide swells, filter movement and vibrato on lead sounds. Choose polyphonic aftertouch when you want to bring out individual notes inside chords. For deeper per-note pressure and pitch control, the 49-key Expressive E Osmose was €1,599 including VAT at Thomann on November 11, 2026, while the more conventional ASM Hydrasynth Keyboard was €1,269 including VAT at Thomann on November 11, 2026.
Explore Per-Note Control With Osmose
Osmose combines polyphonic aftertouch with deeper pressure and lateral key movement. See its current price and availability at Thomann.
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