/**

* Audio analyser: provide RMS levels + filters / derivatives.

*/

ThreeAudio.LevelDetect = function (data) {

this.data = data;

this.levels = [[0, 0, 0, 0]];

this.smooth = [0, 0, 0, 0];

this.change = [0, 0, 0, 0];

// Add output structure to data.

data.levels = {

direct: this.levels[0],

smooth: this.smooth,

change: this.change,

};

};

ThreeAudio.LevelDetect.prototype.analyse = function () {

var data = this.data,

levels = this.levels,

smooth = this.smooth,

change = this.change,

bins = [0, 0, 0, 0];

// Calculate RMS of time data.

function rms(data) {

var size = data.length, accum = 0;

for (var i = 0; i < size; ++i) {

var s = (data[i] - 128) / 128;

accum += s*s;

}

return Math.sqrt(accum / size);

}

// Calculate energy level for all bins.

var waveforms = [data.time, data.filter.bass, data.filter.mid, data.filter.treble];

for (var j = 0; j < 4; ++j) {

bins[j] = rms(waveforms[j]);

}

// Keep 7 last level values

levels.unshift(bins);

if (levels.length > 7) levels.pop();

// Filter helpers

var accum, factors, gain, decay, samples;

// Calculate averages over 3 frames

factors = [1, 2, 1], gain = 4, samples = Math.min(levels.length, factors.length);

for (var i = 0; i < 4; ++i) {

accum = 0;

for (var j = 0; j < samples; ++j) {

accum += (levels[j] && levels[j][i] || 0) * factors[j];

}

smooth[i] = accum / gain;

}

// Calculate difference over 6 frames

factors = [1, 3, 2, -2, -3, -1], gain = 1, decay = .5, samples = Math.min(levels.length, factors.length);

for (var i = 0; i < 4; ++i) {

accum = 0;

for (var j = 0; j < samples; ++j) {

accum += (levels[j] && levels[j][i] || 0) * factors[j];

}

// Apply additional decay filter to make less erratic.

change[i] = change[i] + (accum / gain - change[i]) * decay;

}

// Write results to data structure.

this.data.levels.direct = this.levels[0];

// Smooth / change updated by reference.

}