code: function MixSilenceIntoBuf(ch, start, end, dataL, dataR) {
    var s = ch.filterstate[1];
    if (isNaN(s)) {
      console.log("NaN filterstate?", ch.filterstate, ch.filter);
      return;
    }
    for (var i = start; i < end; i++) {
      if (Math.abs(s) < 1.526e-5) {  // == 1/65536.0
        s = 0;
        break;
      }
      dataL[i] += s * ch.vL;
      dataR[i] += s * ch.vR;
      s *= popfilter_alpha;
    }
    ch.filterstate[1] = s;
    ch.filterstate[2] = s;
    if (isNaN(s)) {
      console.log("NaN filterstate after adding silence?", ch.filterstate, ch.filter, i);
      return;
    }
    return 0;
  }
docs: This function gradually brings the channel back down to zero if it isn't already to avoid clicks and pops when samples end.