Timbre.js

system requirements: Chrome 14- or Firefox 4-

// rhythm sequencer

// extern p = [ /* ui.checkbox */ ];
var bpm = 132;
var seq, s1, s2, hh, hh_env, sd, sd_env, bd, bd_env;
var metro, drumkit, beam;

// sequence
seq = T("+");

// sequence(1)
s1 = function(freq) {
    var s1, env;
    s1 = T("*", T("fami", freq, 0.6),
                T("*", T("pulse", 12), env = T("perc", 120))).appendTo(seq);
    env.addEventListener("~ended", function() {
        seq.remove(s1);
    }).bang();
};
s1.freqs = [ 880, 440, 880*2, 220, 880*2, 660, 880*2, 660 ];
s1.i = 0;

// sequence(2)
s2 = function() {
    var s2, env;
    s2 = T("*", T("saw", T("ease", "cubic.out", 300, 880*4, 220).bang(), 0.4),
                env = T("perc", 300)).appendTo(seq);
    env.addEventListener("~ended", function() {
        seq.remove(s2);
    }).bang();
};
s2.i = 1;

// hihat
hh = T("*", T("hpf", 8000, T("noise")),
            hh_env = T("perc", "32db", 30));
hh.i = 2;

// snare
sd = T("*", T("rlpf", 5000, 0.4, T("pink")),
            sd_env = T("perc", "32db", 120));
sd.i = 3;

// bass drum
bd = T("clip", T("*", T("rlpf", 40, 0.5, T("pulse", 40, 2)),
                      bd_env = T("perc", "32db", 60)));
bd.i = 4;

// metro
metro = T("interval", timbre.utils.bpm2msec(bpm, 16), function() {
    var i = metro.count % p[0].length;
    
    if (p[s1.i][i]) s1(s1.freqs[i & 7]);
    if (p[s2.i][i] || beam) s2();
    beam = false;
    
    if (p[hh.i][i]) {
        hh_env.mul = [0.4, 0.6][i & 1];
        hh_env.bang();
    }
    if (p[sd.i][i]) {
        sd_env.mul = [0.4, 0.2][i & 1];
        sd_env.d   = [180, 120][i & 1];
        sd_env.bang();
    }
    if (p[bd.i][i]) {
        bd_env.bang();
    }
});

// drumkit
drumkit = T("dac", seq, hh, sd, bd);

drumkit.onbang = function() {
    beam = true;
};
drumkit.onplay = function() {
    interval.on();
};
drumkit.onpause = function() {
    interval.off();
};

drumkit.play();