A CLI sine sweep in Swift

sine-sweep.swift

//------------------------------------------------------------------------------
import AVFoundation
//------------------------------------------------------------------------------
var secondsOfAudio:Float = 0.5; // or var secondsOfAudio:Float = Float(CommandLine.arguments[1])!;
//------------------------------------------------------------------------------
var ae:AVAudioEngine? = AVAudioEngine()
var player:AVAudioPlayerNode? =  AVAudioPlayerNode()
var mixer:AVAudioMixerNode? = ae?.mainMixerNode;
//------------------------------------------------------------------------------
let sr:Float = Float((mixer?.outputFormat(forBus: 0).sampleRate)!)
let samplesOfAudio = UInt32 (secondsOfAudio * sr)
let n_channels = mixer?.outputFormat(forBus: 0).channelCount
var buffer:AVAudioPCMBuffer? = AVAudioPCMBuffer(pcmFormat: (player?.outputFormat(forBus: 0))!, frameCapacity: samplesOfAudio)
buffer?.frameLength = samplesOfAudio
//------------------------------------------------------------------------------
func convertToRange(number: Float, min: Float, max:Float) -> Float {
    return (number - min) / (max - min)
}
//------------------------------------------------------------------------------
// generate sine wave
for i in stride(from:0, to: Int((buffer?.frameLength)!), by: Int(n_channels!))
{
    for n in 0..<n_channels!
    {
        let scale = convertToRange(number: Float(i),
                                   min: 0,
                                   max: Float((buffer?.frameLength)!/2));
        let freq = ((Float(n+1) * scale) + 1) * 441.0
        let val = sinf(freq*Float(i)*2*Float(Double.pi)/sr)
        buffer?.floatChannelData![Int(n)][i] = val * 0.5
    }
}
//------------------------------------------------------------------------------
// setup audio engine
ae?.attach(player!)
ae?.connect(player!, to: mixer!, format: player?.outputFormat(forBus: 0))
do{
    try ae?.start()
} catch {
}
//------------------------------------------------------------------------------
// play player and buffer
player?.play()
player?.scheduleBuffer(buffer!, at: nil, options: .interrupts, completionHandler: {
    player = nil
})

while(player != nil){}
//------------------------------------------------------------------------------