Aftertouch and Velocity Curves Explained for Producers

What is the difference between velocity and aftertouch?

Velocity is a single number captured the moment a key or pad is struck. Aftertouch is a stream of pressure values sent while you hold the key down. Velocity shapes the start of a note; aftertouch shapes what happens during it.

In the MIDI 1.0 message summary, velocity travels inside the Note On message, while pressure has its own messages: Polyphonic Key Pressure and Channel Pressure, both described as most often sent by pressing down after the key bottoms out^[1]. Note Off messages carry a velocity value too, which some instruments use for release behavior.

What is channel aftertouch vs polyphonic aftertouch?

Channel aftertouch sends one pressure value for the whole channel, based on the key you press hardest. Polyphonic aftertouch sends a separate value for each held key.

The MIDI Association describes Channel Pressure as sending the single greatest pressure value of all currently pressed keys, and Polyphonic Key Pressure as carrying a key number plus a pressure value^[1]. In practice, channel aftertouch on a held chord pushes the same vibrato into every note. Poly aftertouch lets you lean on the top note of the chord while the others stay still.

Which hardware sends which?

Check the spec sheet for the exact wording. Arturia lists polyphonic aftertouch on the MicroFreak's 25-key capacitive keybed^[2], and Novation lists polyphonic aftertouch on the 16 pads of the Launchkey Mini^[3]. When a product page only says "aftertouch", as Novation's Bass Station II page does^[4], check the manual or MIDI implementation chart to confirm which type it sends.

Does your instrument respond to it?

The receiving synth decides what pressure does. Some plugins only listen to channel pressure, some to poly pressure, and some to neither until you assign it in the modulation matrix. A keyboard that sends poly aftertouch into a synth that only understands channel pressure behaves like a channel aftertouch keyboard, or does nothing.

What is a velocity curve on a MIDI keyboard?

A velocity curve is the rule that turns how hard you play into a velocity value up to 127. Changing the curve does not change the keys, it changes how easily you reach loud and soft values.

Light-action keyboards and pads often feel too loud or too quiet out of the box because the default curve does not match your touch. Most controllers offer a few presets in their settings or editor app, and your DAW can reshape velocity again after it arrives.

How do you set the right velocity curve?

Fix the curve on the controller first, then fine-tune in the DAW. Adjusting in both places at once makes it hard to know which change helped.

1. Measure your range
   Play 16 notes as softly as you comfortably can, then 16 as hard as you would in a real take. Read the velocities in the piano roll. A healthy spread is roughly 20 to 40 for soft and 100 to 120 for hard.
2. Change the controller curve
   If soft notes land above 50, choose a harder curve. If hard notes rarely pass 90, choose a softer one. Repeat the test.
3. Use the DAW curve if needed
   FL Studio's MIDI settings include a Curve editor that sets the relationship between the controller's note-on velocity and the value passed to FL Studio^[5]. In Ableton Live, place the Velocity MIDI effect before the instrument.
4. Shape per instrument
   In Live's Velocity device, Out Hi and Out Low constrain output, for example 80 to 127 so soft playing still sounds solid, while Drive and Compand push or compress values inside the curve. Fixed mode sends the Out Hi value for every note^[6].
5. Save it
   Save the controller setting as a preset and put the DAW curve in your default template so every session starts the same way.

For drums, velocity editing after recording matters as much as the curve; our sibling guide to velocity in drum programming covers accent patterns and ghost notes.

What should you map velocity and aftertouch to on a synth?

Map velocity to things that should be decided at the start of a note, such as loudness and attack brightness. Map aftertouch to things that should change while the note holds, such as vibrato and filter swell.

Most synths expose both as modulation sources. Ableton's Drift, for example, lists Velocity as a source where higher note velocities produce more modulation, alongside Pressure and Slide^[7]. Start with small amounts: expression that is too strong makes every mistake audible.

• Velocity to amp level The default on most patches. For pads, reduce it so soft notes do not vanish; for keys and plucks, keep it high.
• Velocity to filter envelope amount Harder notes open brighter. Try a modest amount, around 20 to 40 percent, for basses and plucks.
• Velocity to sample start or layer Common in drum and piano instruments, where hard hits trigger a different sample.
• Aftertouch to vibrato depth Press into long lead notes to add vibrato only when you want it. Keep the LFO around 5 to 6 Hz as a starting point.
• Aftertouch to filter cutoff Swells pads and brass-like patches. Limit the range so full pressure does not blow out the top end.
• Aftertouch to wavetable position or FX send Adds movement or space on held notes without drawing automation.

Aftertouch shares the same idea as a mod wheel, just controlled by pressure. If you would rather draw this movement, our sibling article on MIDI CC messages covers CC1 and CC11 lanes.

How does MPE relate to aftertouch?

MPE turns ordinary channel messages into per-note messages by giving each note its own MIDI channel. That makes pressure, pitch bend and timbre independent for every note, which is poly aftertouch plus more.

The MIDI Association states that in MPE each note is assigned its own MIDI channel so messages can be applied to each note individually, that a Registered Parameter Number sets up zones, and that each zone has a master channel for common data such as program changes and pedals. The MMA ratified MPE on January 28, 2018^[8]. In Ableton Live, Analog has an MPE section with pressure, slide and per-note pitch bend, and Drift is described as fully MPE-capable^[7].

You do not need an MPE controller to benefit from pressure. Poly aftertouch covers most per-note swells, and channel aftertouch covers leads and monophonic basses. For MPE setup details, see MPE controller setup in Ableton Live and MIDI 2.0 and MPE for expressive beats.

Why is my aftertouch or velocity not working?

Most problems come from one of three places: the controller is not sending, the DAW is filtering, or the synth has nothing assigned. Check them in that order.

• Aftertouch does nothing Watch the DAW's MIDI monitor while pressing. If no pressure data appears, enable aftertouch in the controller settings. If it appears, assign it in the synth's modulation matrix.
• Every note hits 127 Fixed velocity or a Full Level button is on, or the curve is set too soft. Turn fixed modes off and retest.
• Soft notes are inaudible Raise the lowest output velocity or reduce velocity-to-amp on the synth patch.
• Wobbly pitch on chords Channel aftertouch is mapped to vibrato and you are pressing while holding a chord. Lower the depth or switch to poly aftertouch.
• Huge MIDI clips Pressure sends a stream of values. Thin or delete pressure data you do not need after recording.