RATE=44100,
TEMPO=60/600,
SEMITONE=1.059463094,

song=(t)=>(

// s = sustain/level (0-1)
// d = decay (time)
// n = note (semitones)

// sustain/decay multiplier
decay=(s,d,t)=>max(s*(d-t)/d,0),

U=(n,t)=>t*220*pow(SEMITONE,n),
// sine wave
sw=(n,t)=>sin(U(n,t)*PI*4),
// saw wave
saw=(n,t)=>(u=U(n,t),u%1+u*.996%1-1),
// square wave
sq=(n,t)=>(U(n,t*4)|0)%2,

// sine w/ SDN
f=(s,d,n,t)=>sw(n,t) * decay(s,d,t),
fm=(modS,modD,modN, s,d,n,t)=>sw(n, t + f(modS,modD,n+modN,t)) * decay(s,d,t),

ts=t/44100,
beat=floor(ts/TEMPO),
bprg=ts%TEMPO,
mp=beat%16,
LENGTH=16,
measure=floor(beat/LENGTH),
mprg=ts%(TEMPO*16),
m4=measure%4,
m8=measure%8,

// 0100 1001 0010 1011
bup=(mp%3&1)^(mp>11),
bassnote=[4,4,0,2][m4]-(bup?28:40),

melnote=[0,3,12,8,0,3,8,3][m8]-12,
meln2=[12,7,10,10,12,0,7,5][m8]-12,

mg=(v,l)=>measure>l&&v,

//     MS MD MN CS CD CN t
    fm(-1e-3*bassnote-.017, .4, 0,  .5, .6, bassnote, bprg) + // bassline
    mg(fm(9, 9, 0,  .04, .03, 0, bprg), 7) + // hats
    mg(fm(0,1,0, !(mp&3)*.7, .5, -38, pow(bprg, .6)), -3) + // kick
    mg(fm(.1,1,0, !((mp+4)&7)/4, .2, 0, pow(bprg, .7)), 7) + // snare
    mg(
        saw(m4==3?2:0, mprg) +
        saw(m8==3?5:3, mprg) +
        saw(m8==7?7:(m4<2?7:4+m4*2), mprg),
        15
    )*min(mprg, .4) * decay(.5,2,mprg) + // chords
    mg(
        fm(2e-3,2,0, .5,2,melnote, mprg) +
        fm(2e-3,2,0, meln2&&.5,2,meln2, max(mprg-TEMPO*8,0)),
        23
    ) + // melody
    0
),

//song(t) * 64 + 128;

echo=(t,k)=>(k?song(max(t-k*4200,0))*pow(.3,k)+echo(t,k-1):0),
echo(t,4) * 128 + 128;