Modulation

Modulation routes one signal onto a parameter. The signal is the source. The parameter is the destination. Depth is how far the destination moves. At zero, that routing is silent. Where the control goes negative, the motion runs backwards: an envelope that would open a filter closes it.

An LFO repeats. An envelope runs once per note. Velocity arrives with the note, so harder playing can open a filter without a curve drawn on the timeline. Keyboard tracking follows which note you played, so a filter can open as you go up the keyboard.

A modulation matrix is those connections in one grid. On Heisenberg the cells are operators against operators, and the number in a cell is the depth. On other instruments the cells are source against destination. One cell is one routing. Raise a single cell first, so you can hear that path, before you add another.

Automation writes the same kind of motion onto a timeline lane. It follows the song, and it is the same each time the playhead passes that bar. Modulation stays inside the device and follows each note, so a new note can restart an envelope in the middle of a bar.