Play musical notes in Swift Playground - ios

Question

I am trying to play a short musical note sequence with a default sine wave as sound inside a Swift Playground. At a later point I'd like to replace the sound with a Soundfont but at the moment I'd be happy with just producing some sound.
I want this to be a midi like sequence with direct control over the notes, not something purely audio based. The AudioToolbox seems to provide what I am looking for but I have troubles fully understanding its usage. Here's what I am currently trying
import AudioToolbox
// Creating the sequence
var sequence:MusicSequence = nil
var musicSequence = NewMusicSequence(&sequence)
// Creating a track
var track:MusicTrack = nil
var musicTrack = MusicSequenceNewTrack(sequence, &track)
// Adding notes
var time = MusicTimeStamp(1.0)
for index:UInt8 in 60...72 {
var note = MIDINoteMessage(channel: 0,
note: index,
velocity: 64,
releaseVelocity: 0,
duration: 1.0 )
musicTrack = MusicTrackNewMIDINoteEvent(track, time, &note)
time += 1
}
// Creating a player
var musicPlayer:MusicPlayer = nil
var player = NewMusicPlayer(&musicPlayer)
player = MusicPlayerSetSequence(musicPlayer, sequence)
player = MusicPlayerStart(musicPlayer)
As you can imagine, there's no sound playing. I appreciate any ideas on how to have that sound sequence playing aloud.

Answer 1

You have to enable the asynchronous mode for the Playground.
Add this at the top (Xcode 7, Swift 2):
import XCPlayground
XCPlaygroundPage.currentPage.needsIndefiniteExecution = true
and your sequence will play.
The same for Xcode 8 (Swift 3):
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true

Answer 2

Working MIDI example in a Swift Playground
import PlaygroundSupport
import AudioToolbox
var sequence : MusicSequence? = nil
var musicSequence = NewMusicSequence(&sequence)
var track : MusicTrack? = nil
var musicTrack = MusicSequenceNewTrack(sequence!, &track)
// Adding notes
var time = MusicTimeStamp(1.0)
for index:UInt8 in 60...72 { // C4 to C5
var note = MIDINoteMessage(channel: 0,
note: index,
velocity: 64,
releaseVelocity: 0,
duration: 1.0 )
musicTrack = MusicTrackNewMIDINoteEvent(track!, time, &note)
time += 1
}
// Creating a player
var musicPlayer : MusicPlayer? = nil
var player = NewMusicPlayer(&musicPlayer)
player = MusicPlayerSetSequence(musicPlayer!, sequence)
player = MusicPlayerStart(musicPlayer!)
PlaygroundPage.current.needsIndefiniteExecution = true
Great MIDI reference page with a nice chart