Web midi.js implementing a bass coupler

[jsCoder07]

I am trying to implement a bass and melody coupler. They usually read what the lowest or highest notes on a chord are and then play the last bass note an octave lower. The second detects the last note of the chord and plays that note with a more prominent voice.

I am not sure how to read the last note or the first note of a chord from the midi message as they come in.

Please I'd appreciate your help

[tobyhede]

You probably need to intercept sendNoteOn or playNote.
https://github.com/djipco/webmidi/blob/master/src/OutputChannel.js#L929

Both accept an array of Notes - if a chord is being played I would expect the notes to be in an array. Worth checking to confirm that though.

Once you have the array of notes, you can sort by number.
https://github.com/djipco/webmidi/blob/master/src/Note.js#L271

Once you have the number, there is an offsetNumber helper in Utilities for calculating an offset by octave and/or semitone.
https://github.com/djipco/webmidi/blob/master/src/Utilities.js#L472

Create a new note with the right octave offset, append to the array and everything continues from there.