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diff --git a/src/com/jsyn/unitgen/PitchDetector.java b/src/com/jsyn/unitgen/PitchDetector.java
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+/*
+ * Copyright 2012 Phil Burk, Mobileer Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.jsyn.unitgen;
+
+import com.jsyn.ports.UnitInputPort;
+import com.jsyn.ports.UnitOutputPort;
+import com.jsyn.util.AutoCorrelator;
+import com.jsyn.util.SignalCorrelator;
+
+/**
+ * Estimate the fundamental frequency of a monophonic signal. Analyzes an input signal and outputs
+ * an estimated period in frames and a frequency in Hertz. The frequency is frameRate/period. The
+ * confidence tells you how accurate the estimate is. When the confidence is low, you should ignore
+ * the period. You can use a CompareUnit and a LatchUnit to hold values that you are confident of.
+ * <P>
+ * Note that a stable monophonic signal is required for accurate pitch tracking.
+ * 
+ * @author (C) 2012 Phil Burk, Mobileer Inc
+ */
+public class PitchDetector extends UnitGenerator {
+    public UnitInputPort input;
+
+    public UnitOutputPort period;
+    public UnitOutputPort confidence;
+    public UnitOutputPort frequency;
+    public UnitOutputPort updated;
+
+    protected SignalCorrelator signalCorrelator;
+
+    private double lastFrequency = 440.0;
+    private double lastPeriod = 44100.0 / lastFrequency; // result of analysis
+    private double lastConfidence = 0.0; // Measure of confidence in the result.
+
+    private static final int LOWEST_FREQUENCY = 40;
+    private static final int HIGHEST_RATE = 48000;
+    private static final int CYCLES_NEEDED = 2;
+
+    public PitchDetector() {
+        super();
+        addPort(input = new UnitInputPort("Input"));
+
+        addPort(period = new UnitOutputPort("Period"));
+        addPort(confidence = new UnitOutputPort("Confidence"));
+        addPort(frequency = new UnitOutputPort("Frequency"));
+        addPort(updated = new UnitOutputPort("Updated"));
+        signalCorrelator = createSignalCorrelator();
+    }
+
+    public SignalCorrelator createSignalCorrelator() {
+        int framesNeeded = HIGHEST_RATE * CYCLES_NEEDED / LOWEST_FREQUENCY;
+        return new AutoCorrelator(framesNeeded);
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] inputs = input.getValues();
+        double[] periods = period.getValues();
+        double[] confidences = confidence.getValues();
+        double[] frequencies = frequency.getValues();
+        double[] updateds = updated.getValues();
+
+        for (int i = start; i < limit; i++) {
+            double current = inputs[i];
+            if (signalCorrelator.addSample(current)) {
+                lastPeriod = signalCorrelator.getPeriod();
+                if (lastPeriod < 0.1) {
+                    System.out.println("ILLEGAL PERIOD");
+                }
+                double currentFrequency = getFrameRate() / (lastPeriod + 0);
+                double confidence = signalCorrelator.getConfidence();
+                if (confidence > 0.1) {
+                    if (true) {
+                        double coefficient = confidence * 0.2;
+                        // Take weighted average with previous frequency.
+                        lastFrequency = ((lastFrequency * (1.0 - coefficient)) + (currentFrequency * coefficient));
+                    } else {
+                        lastFrequency = ((lastFrequency * lastConfidence) + (currentFrequency * confidence))
+                                / (lastConfidence + confidence);
+                    }
+                }
+                lastConfidence = confidence;
+                updateds[i] = 1.0;
+            } else {
+                updateds[i] = 0.0;
+            }
+            periods[i] = lastPeriod;
+            confidences[i] = lastConfidence;
+            frequencies[i] = lastFrequency;
+        }
+    }
+
+    /**
+     * For debugging only.
+     * 
+     * @return internal array of correlation results.
+     */
+    public float[] getDiffs() {
+        return signalCorrelator.getDiffs();
+    }
+
+}