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diff --git a/src/com/jsyn/unitgen/RaisedCosineEnvelope.java b/src/com/jsyn/unitgen/RaisedCosineEnvelope.java
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+/*
+ * Copyright 2011 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;
+
+/**
+ * An envelope that can be used in a GrainFarm to shape the amplitude of a Grain. The envelope
+ * starts at 0.0, rises to 1.0, then returns to 0.0 following a cosine curve.
+ * 
+ * <pre>
+ * output = 0.5 - (0.5 * cos(phase))
+ * </pre>
+ * 
+ * @author Phil Burk (C) 2011 Mobileer Inc
+ * @see GrainFarm
+ */
+public class RaisedCosineEnvelope extends GrainCommon implements GrainEnvelope {
+    protected double phase;
+    protected double phaseIncrement;
+
+    public RaisedCosineEnvelope() {
+        setFrameRate(44100);
+        setDuration(0.1);
+    }
+
+    /**
+     * @return next value of the envelope.
+     */
+    @Override
+    public double next() {
+        phase += phaseIncrement;
+        if (phase > (2.0 * Math.PI)) {
+            return 0.0;
+        } else {
+            return 0.5 - (0.5 * Math.cos(phase)); // TODO optimize using Taylor expansion
+        }
+    }
+
+    /**
+     * @return true if there are more envelope values left.
+     */
+    @Override
+    public boolean hasMoreValues() {
+        return (phase < (2.0 * Math.PI));
+    }
+
+    /**
+     * Reset the envelope back to the beginning.
+     */
+    @Override
+    public void reset() {
+        phase = 0.0;
+    }
+
+    @Override
+    public void setDuration(double duration) {
+        phaseIncrement = 2.0 * Math.PI / (getFrameRate() * duration);
+    }
+
+}