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diff --git a/src/com/jsyn/unitgen/EdgeDetector.java b/src/com/jsyn/unitgen/EdgeDetector.java
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+/*
+ * Copyright 1997 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;
+
+/**
+ * Output 1.0 if the input crosses from zero while rising. Otherwise output zero. The output is a
+ * single sample wide impulse. This can be used with a Latch to implement a "sample and hold"
+ * circuit.
+ * 
+ * @author (C) 1997-2010 Phil Burk, Mobileer Inc
+ * @see Latch
+ */
+public class EdgeDetector extends UnitFilter {
+    private double previous = 0.0;
+
+    /* Define Unit Ports used by connect() and set(). */
+    public EdgeDetector() {
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] inputs = input.getValues();
+        double[] outputs = output.getValues();
+
+        for (int i = start; i < limit; i++) {
+            double value = 0.0;
+            double in = inputs[i];
+            if ((previous <= 0.0) && (in > 0.0)) {
+                value = 1.0;
+            }
+            outputs[i] = value;
+            previous = in;
+        }
+    }
+}