Each entry in the patch map translation table can have an associated key map. Key maps affect note-on, note-off, and polyphonic-key-aftertouch messages. A key map has a translation table with an entry for each of the 128 MIDI key values. For example, if the entry for key value 60 is 72, then the Mapper modifies MIDI note-on messages, as shown in the following illustration:
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Key maps are useful with synthesizers having key-based percussion instruments where a particular percussion sound is assigned to each key. Key maps are usually assigned to the first patch in the patch maps on the percussion channels (10 and 16).