A destination program-change valueEach channel map entry can have an associated patch map. Patch maps affect MIDI program-change and volume-controller messages. Program-change messages tell a synthesizer to change the instrument sound for a specified channel. Volume-controller messages set the volume for a channel.
A patch map has a translation table with an entry for each of the 128 program-change values. Each patch map specifies the following:
A destination program-change value
A volume scalar
An optional key map
When program-change messages are received by the MIDI Mapper, the destination program-change value is substituted for the program-change value in the message. For example, if the destination program-change value for program-change 16 is 18, the Mapper modifies the MIDI program-change message, as shown in the following illustration:
The purpose of the volume scalar is to allow adjustments between the relative output levels of different patches on a synthesizer. For example, if the bass patch on a synthesizer is too loud compared to its piano patch, you can change the setup map to scale the bass volume down or the piano volume up.
The volume scalar specifies a percentage value for changing all MIDI main-volume controller messages that follow an associated program-change message. For example, if the volume scalar value is 50%, then the Mapper modifies MIDI main-volume controller messages, as shown in the following illustration: