W. J. Melvin
W. J. Melvin Musician, producer, sound engineer, composer, chief of MIDI technology @beat_bars

How do you use Pitch Bend and Aftertouch?

In previous articles, we discussed most types of Channel Voice Messages. We described Note-On / Note-Off, Control Change and Program Change in detail. Today’s post will be devoted to last three types of Channel Voice Messages — Pitch Bend and two types of Aftertouch: Channel Pressure and Polyphonic Key Pressure.

Conceptually and technically they do not differ much from CC messages, so if you have read our post on this topic, it won’t be difficult to understand them.

Pitch Bend

Mod wheel

It is used to smoothly raise and lower the pitch of the sound.

In MIDI keyboards, this type of message is usually generated by means of a wheel next to the Modulation Wheel, which we wrote about earlier.

The Pitch Bend wheel can usually be tilted forward and backward, and position 0 is in the middle. Turning the wheel forward raises the pitch, and turning it backward lowers the pitch.

Similarly to the case of CC — the movement of the wheel sends the entire MIDI message stream with values corresponding to its tilt.

In addition, the wheel springs back and automatically returns to the centre to position 0. However, this is not a rule — you can generate a Pitch Bend message using other knobs or expression pedals without automatic return and in such a situation it’s worth configuring the controller to only raise or lower the pitch.

The Pitch Bend message differs from CC mainly in accuracy. The values it sends are numbers in the range of -8192 to +8191 (and not as in the case of CC 0–127).

Such resolution is enough to make pitch changes occur in a continuous manner rather than in steps. Negative values lower the pitch and positive values increase it.

pitch bend automation
Pitch Bend

And what is the relationship between these values and the pitch of sound?

As usual — it depends on the recipient — the sound module or the DAW. Most often, the maximum value of +8191 increases the pitch by two semitones (one tone) and -8192 decreases it by the same interval, but you can configure the MIDI receiver so that the maximum tilt raises the pitch by only one semitone or by even a few octaves (this is when the high resolution of the value of this message comes in useful).

EX2M MIDI USB adapter
Expression pedal to MIDI adapter

If the firmware allows it, as in the case with the EX2M Adapter, Pitch Bend can also be configured on the sender’s side so that the wheel, slider, knob or expression pedal will send values with a limited range, e.g. from 0 to 4095.

This will (for the recipient’s default settings) raise the pitch by one semitone and prevent it from being lowered.

Just to clarify — this is not an analogue change in tone as in the case of the whammy effect, or digital signal processing as in the case of pitch correction plug‑ins — these are only control messages and all responsibility for their correct interpretation and extraction of sound at the appropriate pitch is on the side of the sound module or DAW.


After touch

This message, as the name suggests, originally was to be sent by MIDI keyboards after pressing a key. After hitting the keyboard-controller key, it sends a Note-On message followed by an Aftertouch MIDI message stream depending on the pressure on the key. In this way, you can get an interesting vibrato or other modulation with different depths.

There are two variants of this message — one sends only the values associated with the variable pressure, and the other one sends along with this value information on which key (note) these changes apply to.

The first type — Channel Pressure — is not different conceptually from the CC message. It is like tilting the modulation wheel just after hitting a key, but here you can do it with the same finger which is playing by pressing the key harder or lighter. If you play a chord, or just a lot of different keys at once, the Aftertouch message series will apply to all keys together, i.e. the entire channel (there will be more on channels in one of the next posts) — one common Aftertouch event series will be sent.

Channel pressure

The second type — Polyphonic Key Pressure — sends a separate series of Aftertouch values changes for each key separately. Each of the simultaneously pressed keys can then modulate independently, which is not the case in Channel Pressure, where they modulate synchronously.

Again — as in any type of MIDI message — the message itself, as a series of data, does not define how it is supposed to affect the sound. It only sends information that these changes should take place. The recipient — software or hardware — decides how to interpret these signals.

In the next MIDI article, we will talk about Channel Mode Messages (as opposed to Channel Voice Messages, which we have written about so far), and MIDI Channels (finally), as well as physical connections of MIDI devices — wired and wireless.

Stay tuned. ⏰🖐

MIDI controllers