How to play multiple sounds from buffer simultaneously using nodes connected to AVAudioEngine's mixer

Question

I am making a basic music app for iOS, where pressing notes causes the corresponding sound to play. I am trying to get multiple sounds stored in buffers to play simultaneous

Answer 1

It turns out that having the .interrupt option wasn't the issue (in fact, this actually turned out to be the best way to restart the sound that was playing in my experience, as there was no noticeable pause during the restart, unlike the stop() function). The actual problem that was preventing multiple sounds from playing simultaneously was this particular line of code.

// One AVAudioPlayerNode per note
    var audioFilePlayer: [AVAudioPlayerNode] = Array(repeating: AVAudioPlayerNode(), count: 7)

What happened here was that each item of the array was being assigned the exact same AVAudioPlayerNode value, so they were all effectively sharing the same AVAudioPlayerNode. As a result, the AVAudioPlayerNode functions were affecting all of the items in the array, instead of just the specified item. To fix this and give each item a different AVAudioPlayerNode value, I ended up changing the above line so that it starts as an empty array of type AVAudioPlayerNode instead.

// One AVAudioPlayerNode per note
    var audioFilePlayer = [AVAudioPlayerNode]()

I then added a new line to append to this array a new AVAudioPlayerNode at the beginning inside of the second for-loop of the viewDidLoad() function.

// For each note, attach the corresponding node to the audioEngine, and connect the node to the audioEngine's mixer.
for i in 0...6
{
    audioFilePlayer.append(AVAudioPlayerNode())
    // audioEngine code
}

This gave each item in the array a different AVAudioPlayerNode value. Playing a sound or restarting a sound no longer interrupts the other sounds that are currently being played. I can now play any of the notes simultaneously and without any noticeable latency between note press and playback.