MIDI Pitch Bend

MIDI normally only allows the notes of a traditional western scale. The MIDIUSB library includes a table of MIDI note numbers to note names, telling you what notes you can play with noteOn and noteOff messages. But you can get other pitches using pitch bend.

You play a note on channel 0 with a command like this:

midiCommand(0x90, pitch, velocity);

Then to bend the pitch on channel 0, you send a pitch bend message like this:

midiCommand(0xE0, lsb, msb);

lsb and msb are the least significant byte and most significant byte of a 14-bit number. Note that most computers store numbers as 8-bit numbers, so you’ll need to convert the bytes before you send them.

Pitch bend can bend up or down. Most synthesizers will bend up to +/-2 semitones. So max pitch bend down takes the note down two semitones. Max pitch bend up takes it up two semitones. A pitch bend value of 8192 represents no pitch bend. For example, if you want a pitch between C4 and C#4, you would play C4, then pitch bend up a little. For example:

midiCommand(0x90, 60, 127);  // play C4 as loud as possible
midiCommand(0xE0, 39, 64);  // a little pitch bend up

Or to play between C4 and B3, the note below it, you would pitch bend down:

midiCommand(0x90, 60, 127);  // play C4 as loud as possible
midiCommand(0xE0, 100, 63);  // a little pitch bend down

How do you get the pitch bend values? Pitch bend has a 14-bit range, from 0 - 16383. The two data bytes combined make the pitch bend value. A pitch bend of 0 bends 2 semitones down, while 16383 bends almost 2 semitones up. In other words, C4 plus pitch bend of 16383 is D4, and C4 plus pitch bend of 0 is Bb3.

Now, you might think, “okay, I’ll just read an analog sensor and map it from 0-1023 to 0-16384”. That’s a start, but remember, MIDI data bytes are 7-bit, not 8-bit, like normal. This is where you need to know about converting 8-bit values to 7-bit. This is where the conversion of 8-bit values to 7-bit for MIDI (midi-bit-shifting.html) will help.

For a simple pitch bend example, see the MIDIUSBPitchBend example.