This is the simple way - This function connects the first available midi input to first available midi output. You can set all midi thru params like sources and destinations in this example.     func makeMidiThru() -> OSStatus {         var connectionRef: MIDIThruConnectionRef = 0         var params = MIDIThruConnectionParams()         MIDIThruConnectionParamsInitialize(&params) 				params.numSources = 1         params.numDestinations = 1         params.sources.0.endpointRef = MIDIGetSource(0)         params.destinations.0.endpointRef = MIDIGetDestination(0)         let paramsData = withUnsafePointer(to: params) { p in             Data(bytes: p, count: MIDIThruConnectionParamsSize(&params))         }         return MIDIThruConnectionCreate(nil, paramsData as CFData, &connectionRef)     }

For high precision, steady timer, I like to use the DispatchSource API. I use it for precision clocking, or when I need a timer to run during a control drag. There is certainly other smarter ways to update the UI. The leeway also has a minimal value, check the 'DispatchSourceTimer' documentation for all details. let queue = DispatchQueue(label: "com.myCompany.myApp.timerQueue",                           qos: .userInteractive,                           attributes: [],                           autoreleaseFrequency: .inherit,                           target: nil) let timer = DispatchSource.makeTimerSource(flags: .strict, queue: queue) var counter: Int = 0 timer.schedule(deadline: DispatchTime.now(), repeating: DispatchTimeInterval.nanoseconds(periodInNanoseconds), leeway: DispatchTimeInterval.nanoseconds(1)) timer.setEventHandler { // Do something at high rate in the queue counter+=1 if counter % 10000 == 0 { DispatchQueue.main.async { // Do something in the main queue ( UI Update ) } } }         timer.resume()