function envelope(start){
var totalDuration = durs.reduce(function(e,i){return e + i}, 0);
tdNormFN = tnorm(start, totalDuration);
var s = 0;
durFNS = durs.map(function(e,i){
var x = tnorm(start + s, e)
s += e;
return x
})
durpercent = durs.map(function(e, i){return e / totalDuration})
var tn = 0, n, i, fn = 0;
return function(t){
tn = tdNormFN(t);
if(1 < tn || tn < 0) return 0
if(tn > durpercent[fn]) fn = (++fn > pts.length - 1 ? 0 : fn)
return pts[fn](durFNS[fn](t))
}
}
durFNS = durs.map(function(e,i){
var x = tnorm(start + s, e)
s += e;
return x
})