/ Reference / MIDI CC

Contents: MIDI 1.0 | MIDI Polyphonic Expression

MIDI 1.0

TL;DR

• MIDI 1.0 has 16 channels (1-16). All midi events are directed toward a single channel.
• MIDI Events/Messages are comprised of multiple (usually 3) fields.
  • The first field is the Status Code which represents 16 channels of 7 categories of events.
  • The number and interpretation of extra fields depends upon the event category.
• NoteOn + NoteOff are the most common/important events.
  • notes are identified by a number in the range 0-127 and map to frequencies according to a 12 tone piano scale, with A4 (440 Hz) represented by the number 69 and middle C by 60.
  • a velocity between 0 and 127 accompanies NoteOn and NoteOff events. A velocity 0 is provided to the NoteOn event is interpretted as NoteOff.
• MIDI 2.0 was recently (2020) announced but will take a while to become relevant.
• MPE is a standardized convention to convey Polyphonic Expression between controllers and instruments that can operate within the MIDI 1.0 ecosystem.
• Online Cheat Sheet

Status codes

ControlChange (CC)

Status bytes 176-191 means channel 1-16.

Example

MIDI 1 CC Spec

Here is code from midiDevice that converts MidiMsg to CC names and values:

// current we skipp the LSB fields
if(this.cc.id < 32 || this.cc.id > 63)
{
    this.midiMsg.data3 / 127.0 => cc.value;
    "CC"+id => this.cc.name;
}

And here is a table based on original MIDI spec names.

Pitch Wheel Value Interpretation

PitchBend (mod-wheel CC 176/1) are usually 7 bit precision (0 to 127) while PitchWheel (not a CC, but a first-class status message) are always 14 bits (0 to 16383). Depending on the MIDI devices, this value range may correspond to bending of +/- 1 or 2 tones, but this range can be customized.

Combine lsb and msb to produce a 14-bit value.

The center value (no pitch change) is 0x2000 (8192).

It is up to the device to translate this to a specific pitch. For example, 8192 represents no change in pitch and 0 decimal is two semitones lower and if the pitch is computed exponentially, then -812 will represent a drop in the pitch of a little less than 20 cents.

Aftertouch (pressure)

160-175: xA0-xAF is polyphonic aftertouch. It applies to individual notes in the channel. data1 is the note-number and data2 is the pressure (0-127).

208-223, xD0-xDF is channel aftertouch. It applies to all notes in the channel. Pressure value is found in data1 and its range is therefore 0-127.

Example: note and control sequence Akai MPK mini

meta

In the context of Fiddle, meta-messages can occur when "performing" an abc file.

MIDI Polyphonic Expression (MPE)

what is mpe?

When a device is transmitting MIDI according to MPE, it will use a range of channels:

One channel (usually Channel 1) is used for global messages – data such as preset changes and pedal positions are transmitted on this channel to apply to all notes equally. The global channel is set by the "MPE Zone." When the MPE Zone is the Lower Zone, Channel 1 is used for global messages. When the MPE Zone is Upper Zone is, Channel 16 is used for global messages.

The remaining channels (usually Channels 2–16) are used to transmit notes and expressive data – including note-on velocity, pitch bend, channel pressure (aftertouch), CC74 (brightness), and note-off (release) velocity – on a note-per-channel basis. The expressive data will only apply to the note which is on the same channel.

Tidbits from the MPE Spec

This specification is designed for MIDI controllers that allow the performer to vary the pitch and timbre of individual notes while playing polyphonically.

…

MIDI Pitch Bend and Control Change messages are Channel Messages, meaning they affect all notes assigned to that Channel. To apply Channel Messages to individual notes, an MPE controller assigns each note its own Channel.

…

Pitch Bend is, by default, set to a range of ±48 semitones for per-note bend and ±2 semitones for Master bend. Either range may be changed to a number of semitones between 0 and ±96 using RPN 0.

• Aftertouch is sent using the Channel Pressure message. To preserve compatibility with existing MIDI devices, Polyphonic Key Pressure may be used with notes on the Master Channel, but not on other Channels.
• In addition to being able to express per-note pitch (Pitch Bend) and pressure (Channel Pressure), a third dimension of per-note control may be expressed using MIDI CC #74 (brightness).

…

Simple circular assignment of new notes to Member Channels of a Zone will not usually provide satisfactory results. In the simplest workable implementation, a new note will be assigned to the Channel with the lowest count of active notes. Then, all else being equal, the Channel with the oldest last Note Off would be preferred. This set of rules has at least one working real-world implementation.

MPE controllers should preferentially re-use a Channel that has been most recently deployed to play a certain Note Number once the previous note has entered its Note Off state. This avoids stacking and chorusing identical notes, which sounds bad in monotimbral applications, and affects synthesizers that are not designed specifically for MPE

MPE Example: Roli Lightpad Block

Quick touch of top-left 'note'

Quick touch/dragdown of top-left 'note'

Quick touch/dragdown of two top-left 'notes'