Sounds play delay wrong - actionscript-3

Question

I am writing simple metronome component using Flex + AS3. I want it playing 'tick1' sound after, for example, each 500 millisecond and each 4th time plays another sound 'tick2'. But actually delay between sound is not equivalent - sometimes lesser, sometimes greater a bit. I testing it on latest Chrome.
Here my code:
//Somewhere here button bound to the 'toggle' function
import flash.utils.Timer;
import flash.events.TimerEvent;
import flash.media.SoundTransform;
import flash.media.SoundChannel;
private var bpm:Number = 120; //2 bit per second, delay=500ms
private var period:Number = 4;
private var timer:Timer = new Timer(bpm, period);
[Embed(source='sounds/1.mp3')]
private var tickSound1Class:Class;
private var tickSound1:Sound;
[Embed(source='sounds/2.mp3')]
private var tickSound2Class:Class;
private var tickSound2:Sound;
private var trans:SoundTransform = new SoundTransform(1);
private function init():void {
....
tickSound1 = new tickSound1Class() as Sound;
tickSound2 = new tickSound2Class() as Sound;
update();
timer.addEventListener(TimerEvent.TIMER, onTimerEvent);
....
}
private function update():void {
timer.delay = 1000 * 60/bpm;
timer.repeatCount = 0;
}
private function toggle():void {
if (timer.running) {
timer.reset();
startStopButton.label = "Start";
} else {
update();
timer.start();
startStopButton.label = "Stop";
}
}
private function onTimerEvent(event:TimerEvent):void {
var t:Timer = event.currentTarget as Timer;
if (t.currentCount % period == 0)
tickSound1.play(0, 0, trans);
else
tickSound2.play(0, 0, trans);
}

Answer 1

I think there are two main reasons:
It is known that Timer object in Flash Player is inaccurate, delay between it's fires fluctuates.
Sound.play() method also introduces some delay before the sound actually starts to play, and theoretically this delay can fluctuate. The delay is especially noticeable in PPAPI version of Flash Player being used in Chrome.
There are several solutions. I would suggest one of these:
Use pre-composed sound of the whole metronome cycle (tick1-pause1-tick2-pause2) and just loop it using the second argument of Sound.play() method;
use dynamic sound generation.
The second option is more flexible but is more difficult to implement. Basicaly, you'll need to create a new instance of Sound object, subscribe to it's SAMPLE_DATA event and call it's play() method. In the handler you'll check event.position / 44.1, which will give you current position of sound generation in ms. Then, if you decide that it's time to play tick1 or tick2 sound, you'll call tickN.extract(event.data, ...), where tickN is tick1 or tick2 Sound object, or write the silence otherwise.
You can read more about dynamic sound generation here.
Also, notice that when you call Sound.play() it returns a SoundChannel object, which has the position property. Is it a position in ms of a sound that is being played (not generated) at the moment, and it is accurate. So, using this property, you can come up with the third approach: create a Sound object and setup a SAMPLE_DATA handler like in the dynamic sound generation solution, but write the silence (zeros) to the event.data object inside the handler all the time. This is needed to obtain a sound channel without actually playing a sound. Then, use high frame rate (60 FPS) and a Timer with the smallest possible delay (1 ms). Each time the Timer fires, check soundChannel.position to determine whether it is time to play the tick sound, and, if it so, just play it like you're doing in your example. This approach is likely to solve the problem of the Timer inaccuracy, but it cannot deal with the delay caused by tickSound.play() method.