Change Instruments in MIDI Tracks with Swift

Hello There! This article assumes that you already have a MiDi track set up in Swift and that you’re only interested in changing the MiDi instrument. Please read my other article if you need a refresher.

Changing Tunes: MIDI Channel Manager

Our focus here is to introduce a MIDI Channel Manager, allowing us to specify the new instrument we want for our music track. It’s a straightforward process that requires just a snippet of code:

    // Setting the instrument to Violin (program number 40) 
    var programChangeMessage = MIDIChannelMessage(status: 0xC0, data1: 40, data2: 0, reserved: 0)
    withUnsafePointer(to: &programChangeMessage) { ptr in
        let status = MusicTrackNewMIDIChannelEvent(track!, 0, ptr)
        if status != noErr {
            print("Error setting program change \(status)")
        }
    }

Show Me The REAL Code

Below is an example of what a complete implementation using would look like. Based upon a lot of the work from my earlier article.

import Foundation
import AudioToolbox

func createPlayer(chords : [[UInt8]]){
    var musicPlayer : MusicPlayer? = nil
    var player = NewMusicPlayer(&musicPlayer)

    player = MusicPlayerSetSequence(musicPlayer!, createMusicSequence(chords: chords))
    player = MusicPlayerStart(musicPlayer!)
}

func createMusicSequence(chords: [[UInt8]] ) -> MusicSequence {

    var musicSequence: MusicSequence?
    var status = NewMusicSequence(&musicSequence)
    if status != noErr {
        print(" bad status \(status) creating sequence")
    }
    
    var tempoTrack: MusicTrack?
    if MusicSequenceGetTempoTrack(musicSequence!, &tempoTrack) != noErr {
        assert(tempoTrack != nil, "Cannot get tempo track")
    }

    //MusicTrackClear(tempoTrack, 0, 1)
    if MusicTrackNewExtendedTempoEvent(tempoTrack!, 0.0, 128.0) != noErr {
        print("could not set tempo")
    }
    if MusicTrackNewExtendedTempoEvent(tempoTrack!, 4.0, 256.0) != noErr {
        print("could not set tempo")
    }
    
    
    // add a track
    var track: MusicTrack?
    status = MusicSequenceNewTrack(musicSequence!, &track)
    if status != noErr {
        print("error creating track \(status)")
    }
    
    
    // Setting the instrument to Violin (program number 40)
    var programChangeMessage = MIDIChannelMessage(status: 0xC0, data1: 40, data2: 0, reserved: 0)
    withUnsafePointer(to: &programChangeMessage) { ptr in
        let status = MusicTrackNewMIDIChannelEvent(track!, 0, ptr)
        if status != noErr {
            print("Error setting program change \(status)")
        }
    }
    
  
    
    // make some notes and put them on the track
    var beat: MusicTimeStamp = 0.0
   
    for batch in 0..<chords.count {
        for note: UInt8 in chords[batch] {
            var mess = MIDINoteMessage(channel: 0,
                                       note: note,
                                       velocity: 64,
                                       releaseVelocity: 0,
                                       duration: 1.0 )
            status = MusicTrackNewMIDINoteEvent(track!, beat, &mess)
            if status != noErr {    print("creating new midi note event \(status)") }
            
        }// beat changes after this
        beat += 1
    }
    
    CAShow(UnsafeMutablePointer<MusicSequence>(musicSequence!))
    
    return musicSequence!
}

✨Yay! We did it!✨

At this point, all you need to do is pass in some chords and listen to the richness of MiDi sound.

✨Congratulations✨