Lesson 15 · Pitch bend - Build a MIDI Parser

Pitch bend

Pitch bend needs more resolution than seven bits, so it splits a 14-bit value across two data bytes, low seven bits first. Today you reassemble that number and pin its center and extremes.

The goal

Parse a pitch-bend event, assembling its two data bytes into a 14-bit value.

Start here - the target

TO DO

Scenario: Two data bytes assemble into a 14-bit bend value

Giventhe three bytes 0xE0 0x00 0x40

Whenthey are parsed as a pitch-bend event

Thenit is pitch bend on channel 0 with value 8192 (center, no bend)

And0xE0 0x00 0x00 is value 0 (fully down) and 0xE0 0x7F 0x7F is value 16383 (fully up)

Background

Pitch bend (high nibble 0xE) sweeps a note’s pitch smoothly, and 128 steps are not enough resolution, so it uses 14 bits spread over its two data bytes. The catch is the order: the first data byte holds the low seven bits (LSB) and the second holds the high seven bits (MSB). Reassemble with msb << 7 | lsb.

The three values to pin are the ones that matter musically: 0x00 0x40 is 8192, the center where the wheel rests and no bending happens; 0x00 0x00 is 0, bent fully down; and 0x7F 0x7F is 16383, bent fully up. Get the shift and the byte order right and those three land exactly. This is the last channel voice message - after today every 0x8 through 0xE status is covered, and you can wire them together with running status.

Make it work

// 0xEn: first data byte is the LOW 7 bits, second is the HIGH 7 bits
lsb := r.NextByte()
msb := r.NextByte()
bend := uint16(msb)<<7 | uint16(lsb) // 0..16383, 8192 is center

CheckpointDONE

You can parse a pitch-bend event into a 14-bit value. Commit and stop here.