Exploring Channel Pressure in MIDI Keyboard Sounds

Understanding Channel Pressure and Aftertouch

Channel Pressure, also known as Aftertouch, is a crucial feature in MIDI keyboards that allows for additional expression in performance. This is detected when you apply pressure to the keys after initially striking them, enabling the control of various sound parameters such as pitch, volume, or effects.

For a detailed explanation of MIDI features, refer to my Quora Profile.

What Does Channel Pressure Do?

Channel Pressure does not generate sound on its own; it acts as a controller. Its exact functionality is determined by how the user assigns it to different parameters. This flexibility is one of the greatest benefits of the MIDI protocol.

For example, you can assign it to the volume of a string sound, allowing you to create swells as you play. With a lead synth, you might assign it to the cutoff filter, enabling you to close or open the filter using aftertouch. You can also use it to create vibrato, which can make for a very expressive and intuitive experience, distinct from using the modulation wheel, another generic MIDI controller that can be assigned to various parameters.

Practical Examples of Channel Pressure

In this sample, I have recorded a demonstration using my Roland XP-30:

I first play and hold a chord normally. This is the base sound without additional expression.

Then I play the same chord again, but this time I apply pressure to the keys. The difference is immediately noticeable. The subtle change in volume or modulation effect brings an added layer of depth and expression to the performance.

Channel Pressure can be used in a variety of ways to enhance the performance. By assigning it to parameters such as volume, filter cutoff, or vibrato, you can add dynamic and expressive elements to your compositions and performances.