# Chapter 4. Midi Maps

# 4.1. What is a midi map ?

A Midi Map is something that maps midi events in other midi events .

This is totally needed if a synthesizer doesn't understand the standard events (that is, if a synthesizer is not General Midi compliant), in this case, a midi map will translate General Midi events in the events that that synthesizer understands.

For example you can make a midi map that converts all the `Change patch to Bright Piano` events, to `Change patch to Trumpet` events, and so when a song tries to play a piano, it will play a trumpet instead.

This may sound odd, (why playing a trumpet when the song is made to play a piano ?), but it is very useful. The GM standard specifies that when a midi keyboard receives an event to change patch to `0`, it will change the current patch to `Grand Piano`, but older synthesizer will change for example to a `Electric Guitar` when it receives a `0`. This old keyboard, needed to receive a `3` (for example) to change to a `Piano`. And here comes the midi map in action, changing all `change patch to 0` to `change patch to 3` and thus really playing the correct instrument when it has to.