diff --git a/jsnes/src/sample.js b/jsnes/src/sample.js
index a1b0886..7b8802c 100644
--- a/jsnes/src/sample.js
+++ b/jsnes/src/sample.js
@@ -38,14 +38,22 @@ Sample.prototype = {
     this.index += this.increment / clocksPerPeriod; 
   },
   reset: function() { this.index = 0; },
+  freqFromTimer: function(timer) {
+    // timer -> frequency
+    // clocksPerPeriodTriangle = 8, clocksPerPeriodPulse = 4
+    // fTriangle = fCPU/(32*(t + 1))
+    // fpulse = fCPU/(16*(t+1)
+    return 1789773 / (4 * this.clocksPerPeriod * (timer + 1));
+  },
   sample: function(timer, maxTimer, volume) {
     const timerIncreasing = maxTimer - timer;
     if (maxTimer !== this.prevMaxTimer) {
       if (this.prevMaxTimer) {
-        var ratio = this.prevMaxTimer < maxTimer ? maxTimer / this.prevMaxTimer : this.prevMaxTimer / maxTimer;
-        var semitoneInterval = 1.059463;
-        if (ratio >= semitoneInterval * 2 || this.clocksSinceMaxTimerChange > 210000 || this.index >= this.samples.length) {
-          this.index = 0;
+        var ratio = this.freqFromTimer(this.prevMaxTimer) / this.freqFromTimer(maxTimer);
+        if (ratio < 1) { ratio = 1/ratio };
+        var significantNoteChange = 1.1;
+        if ((this.clocksSinceMaxTimerChange > 130000) || ratio >= significantNoteChange) {
+          this.reset();
         }
       }
       this.prevMaxTimer = maxTimer;