While not every patch implements all of these messages, these are some very common and desirable messages for a patch to understand:
/gain Controls the Linear Amplitude of the signal output. Should accept an optional second argument to change to a specific amplitude over a number of milliseconds.
/gain Controls the gain in decibels applied to the signal output. 0 dB = unity gain. Should accept an optional second argument to change to a specific amplitude over a number of milliseconds.
/init Brings the module back to the state it is in when it loads.
/tellmeeverything Reports the current state of all variables as OSC messages in the Max Window, and sends them out the rightmost outlet.
/transposition Controls a transposition factor in floating-point semitones. Should accept an optional second argument to change to a specific transposition over a number of milliseconds.
/version Reports the version in the Max window.
/verbose Can be used to toggle the reporting of extra state information to the Max window.
