Playing baudio multiple sounds - linux

Question

I recently discovered baudio NodeJS library that is awesome.
I have the following code:
var baudio = require("baudio")
, b = baudio()
, tau = 2 * Math.PI
;
function playSound (f, duration) {
console.log(f, duration);
b.push(function (t) {
return (square (f) + square (f + 1)) * (t < duration);
function square (freq) {
return Math.sin(tau * t * freq) < 0 ? -1 : 1;
}
});
b.play();
}
playSound(440, 2) will play A key for 2 seconds. This is right. If I make another call to playSound function, no other sounds will be played.
Why? How can I play other sounds after the first one was played or is playing?

Answer 1

Your playSound() function should accept a parameter t in seconds and you can use modulo to replay the sound. For an example of this consider this pluck function:
return function (t, i) {
return pluck(t % 0.5, 100, 10, 10);
}
function pluck (t, freq, duration, steps) {
var n = duration;
var scalar = Math.max(0, 0.95 - (t * n) / ((t * n) + 1));
var sum = 0;
for (var i = 0; i < steps; i++) {
sum += Math.sin(2 * Math.PI * t * (freq + i * freq));
}
return scalar * sum / 6;
}
Use this link to experiment with a live version.
Don't use setTimeout, setInterval, or other kinds of IO in songs. It will perform very poorly because of how baudio interacts with the event loop (it pegs it and there is not a 1:1 correspondence between system time and music time).

Answer 2

If you run playSound(440, 2); and then periodically check b.t, you'll see that it is still increasing after the 2 seconds is up, and if you check top or ps, you'll see that a sox process is still chugging along.
It turns out baudio is pretty much a wrapper around sox, which is sweet, and the baudio::play method returns a reference to a child process running sox.
So anyway, there's likely a better way, but you can make it work by killing the process at the end of your duration and newing up a new process with each call to playSound like:
var baudio = require("baudio");
function square(freq, t) {
return Math.sin(2 * Math.PI * t * freq) < 0 ? -1 : 1;
}
function playSound(f, duration) {
var b = baudio();
b.push(function (t) {
return (square (f, t) + square (f + 1, t)) * (t < duration);
});
var ps = b.play();
setTimeout(function() {
ps.kill('SIGHUP');
b.t = 0;
}
, duration * 1000);
}
playSound(440, 2);
this works in node 0.8.24, but not so well in 0.10.26... not sure why