// A demonstration of how different types of amplitude decay sound.
// I suggested making the Decay and Release phase of the Ditty ADSR an exponential curve by default.
//
// Synthesizers commonly model a "fading" quantity as an exponential curve, since our ears' perception of volume is logarithmic.
// In other words, the greater the amplitude of sound is, the larger a change in amplitude would be necessary for it to be noticable.
//
// Why not simply make all ADSR stages linear and map it to a logarithmic scale afterwards?
// In most cases a linear Attack is still desireable because it "fades in" the sound. Furthermore, if the envelope value is also used
// in other calculations, you have the unexpected shift in the sustain level.
//
// In the analog world, an ADSR generator would commonly produce the exponential stage by RC discharge, while using a current source
// to charge the capacitor linearly.

input.decayType = 0; // min=0, max=1, step=1 (linear, exponential)

const bell = synth.def(class {
    constructor(opt) {
        this.p1 = 0;
        this.p2 = 0;
        this.fm = 3;
        this.time = 0;
    }
    process(note, env, tick, opt) {
        // generate sound
        var o1 = Math.sin(this.p1 * Math.PI * 2);
        var o2 = Math.sin(this.p2 * Math.PI * 2);
        this.p1 += midi_to_hz(note) * ditty.dt * 8;
        this.p2 += midi_to_hz(note) * ditty.dt * (1 + o1 * this.fm);
        this.fm *= .9995;
        
        // generate decay envelope
        var decayLinear = Math.max(1 - this.time * 2, 0);
        var decayExponential = Math.exp(-Math.min(this.time, 1) * 7) - Math.exp(-1 * 7);
        
        var amplitude = input.decayType ? decayExponential : decayLinear;
        
        this.time += ditty.dt;
        return o2 * amplitude;
    }
});

const ns = scale(c4, scales['harmonic_minor'], 3);

loop( () => {
    bell.play(ns.choose(), { attack: 0.001, release: .0, pan: Math.random() * 2 - 1, amp: .5, duration: 2 });
    sleep(Math.random() * .05);
    bell.play(ns.choose(), { attack: 0.001, release: .0, pan: Math.random() * 2 - 1, amp: .5, duration: 2 });
    sleep( .8 );
}, { name: 'bell' });