Category: Voice
Purpose
To set the Pitch Wheel value. The pitch wheel is used to slide a note's pitch up or down in cents (ie, fractions of a half-step). If the device is a MultiTimbral unit, then each one of its Parts may respond differently (or not at all) to Pitch Wheel. The Part affected by a particular Pitch Wheel message is the one assigned to the message's MIDI channel.
Status
0xE0 to 0xEF where the low nibble is the MIDI channel.
Two data bytes follow the status. The two bytes should be combined together to form a 14-bit value. The first data byte's bits 0 to 6 are bits 0 to 6 of the 14-bit value. The second data byte's bits 0 to 6 are really bits 7 to 13 of the 14-bit value. In other words, assuming that a C program has the first byte in the variable First and the second data byte in the variable Second, here's how to combine them into a 14-bit value (actually 16-bit since most computer CPUs deal with 16-bit, not 14-bit, integers):
unsigned short CombineBytes(unsigned char First, unsigned char Second)
{
unsigned short _14bit;
_14bit = (unsigned short)Second;
_14bit <<= 7;
_14bit |= (unsigned short)First;
return(_14bit);
}
A combined value of 0x2000 is meant to indicate that the Pitch Wheel is centered (ie, the sounding notes aren't being transposed up or down). Higher values transpose pitch up, and lower values transpose pitch down.
Errata
The Pitch Wheel range is usually adjustable by the musician on each MIDI device. For example, although 0x2000 is always center position, on one MIDI device, a 0x3000 could transpose the pitch up a whole step, whereas on another device that may result in only a half step up. The GM spec recommends that MIDI devices default to using the entire range of possible Pitch Wheel message values (ie, 0x0000 to 0x3FFF) as +/- 2 half steps transposition (ie, 4 half-steps total range). The Pitch Wheel Range (or Sensitivity) is adjusted via an RPN controller message.