// The benchmark voice: a 2-operator FM pair into a TPT state-variable
// low-pass, with an amp envelope.
let index = param(1.5, 0, 8)
let cutoff = param(2400, 30, 16000)
let res = param(0.3, 0, 0.98)

var pc = 0.0
var pm = 0.0
var ic1 = 0.0
var ic2 = 0.0
var a1 = 0.0
var a2 = 0.0
var a3 = 0.0
var amp = 0.0
var rel = 0.0

fn block() {
    let g = tan(PI * min(cutoff, sample_rate * 0.45) / sample_rate)
    let k = 2.0 - 2.0 * res
    a1 = 1.0 / (1.0 + g * (g + k))
    a2 = g * a1
    a3 = g * a2
    rel = exp(-1.0 / (0.1 * sample_rate))
}

fn voice() {
    let dt = freq / sample_rate
    pm = fract(pm + dt * 2.0)
    pc = fract(pc + dt)
    let x = sin(TAU * pc + index * sin(TAU * pm))
    let v3 = x - ic2
    let v1 = a1 * ic1 + a2 * v3
    let v2 = ic2 + a2 * ic1 + a3 * v3
    ic1 = 2.0 * v1 - ic1
    ic2 = 2.0 * v2 - ic2
    if gate > 0.0 {
        amp = min(amp + 500.0 / sample_rate, 1.0)
    } else {
        amp = amp * rel
    }
    v2 * amp * velocity * 0.3
}