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diff --git a/src/com/jsyn/unitgen/PhaseShifter.java b/src/com/jsyn/unitgen/PhaseShifter.java
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+/*
+ * Copyright 2014 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;
+
+/**
+ * PhaseShifter effects processor. This unit emulates a common guitar pedal effect but without the
+ * LFO modulation. You can use your own modulation source connected to the "offset" port. Different
+ * frequencies are phase shifted varying amounts using a series of AllPass filters. By feeding the
+ * output back to the input we can get varying phase cancellation. This implementation was based on
+ * code posted to the music-dsp archive by Ross Bencina. http://www.musicdsp.org/files/phaser.cpp
+ * 
+ * @author (C) 2014 Phil Burk, Mobileer Inc
+ * @see FilterLowPass
+ * @see FilterAllPass
+ * @see RangeConverter
+ */
+
+public class PhaseShifter extends UnitFilter {
+    /**
+     * Connect an oscillator to this port to sweep the phase. A range of 0.05 to 0.4 is a good
+     * start.
+     */
+    public UnitInputPort offset;
+    public UnitInputPort feedback;
+    public UnitInputPort depth;
+
+    private double zm1;
+    private double[] xs;
+    private double[] ys;
+
+    public PhaseShifter() {
+        this(6);
+    }
+
+    public PhaseShifter(int numStages) {
+        addPort(offset = new UnitInputPort("Offset", 0.1));
+        addPort(feedback = new UnitInputPort("Feedback", 0.7));
+        addPort(depth = new UnitInputPort("Depth", 1.0));
+
+        xs = new double[numStages];
+        ys = new double[numStages];
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] inputs = input.getValues();
+        double[] outputs = output.getValues();
+        double[] feedbacks = feedback.getValues();
+        double[] depths = depth.getValues();
+        double[] offsets = offset.getValues();
+        double gain;
+
+        for (int i = start; i < limit; i++) {
+            // Support audio rate modulation.
+            double currentOffset = offsets[i];
+
+            // Prevent gain from exceeding 1.0.
+            gain = 1.0 - (currentOffset * currentOffset);
+            if (gain < -1.0) {
+                gain = -1.0;
+            }
+
+            double x = inputs[i] + (zm1 * feedbacks[i]);
+            // Cascaded all-pass filters.
+            for (int stage = 0; stage < xs.length; stage++) {
+                double temp = ys[stage] = (gain * (ys[stage] - x)) + xs[stage];
+                xs[stage] = x;
+                x = temp;
+            }
+            zm1 = x;
+            outputs[i] = inputs[i] + (x * depths[i]);
+        }
+    }
+}