A MIDI event that carries the MIDI channel pressure message tells a MIDI device that at a certain time pressure should be applied to one of the MIDI channels similarly to applying pressure to electronic keyboard keys.
This message differs from the MIDI Key Pressure message. The MIDI key pressure message applies pressure to certain notes. The MIDI channel pressure message applies pressure to the whole channel and all its notes.
This message belongs to the category of MIDI voice messages.
The MIDI channel pressure message consists of two bytes of data. The first byte is the status byte and has hexadecimal values between 0xD0 and 0xDF. The high nibble of the status byte is D, which tells the MIDI device that this is a channel pressure message. The low nibble of the status byte is between 0 and F (0 and 15 in decimal values) and points to one of the 16 MIDI channels. One byte follows the status byte and has values between 0x00 and 0x7F (0 and 127 in decimal values). It signifies the amount of pressure, where 0 is least pressure and 127 is most pressure.
Since a MIDI channel pressure message specifies a single amount of pressure a MIDI device must receive numerous MIDI channel pressure events to produce varying pressure.
What a channel pressure message sounds like depends on the device. With the General MIDI 2 standard, the MIDI controller destination message was defined to help standardize device response to the MIDI channel pressure message and other controllers.
The following is an example of a MIDI channel change message.
The status byte 0xD6 shows that this is a channel pressure message for channel 6. The amount of pressure is 0x35.
Musical Instrument Digital Interface (MIDI)