Added a new BrownNoise unit generator that generate

noise based on Brownian motion.

2 files changed, 76 insertions, 0 deletions

diff --git a/src/com/jsyn/unitgen/BrownNoise.java b/src/com/jsyn/unitgen/BrownNoise.java
new file mode 100644
index 0000000..e70b7f4
--- /dev/null
+++ b/src/com/jsyn/unitgen/BrownNoise.java
@@ -0,0 +1,75 @@
+/*
+ * 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;
+
+import com.jsyn.ports.UnitInputPort;
+import com.jsyn.ports.UnitOutputPort;
+import com.jsyn.util.PseudoRandom;
+
+/**
+ * BrownNoise unit. This unit uses a pseudo-random number generator to produce a noise related to
+ * Brownian Motion. A DC blocker is used to prevent runaway drift.
+ * 
+ * <pre>
+ * <code>
+ * output = (previous * (1.0 - damping)) + (random * amplitude) 
+ * </code>
+ * </pre>
+ * 
+ * The output drifts quite a bit and will generally exceed the range of +/1 amplitude.
+ * 
+ * @author (C) 1997-2011 Phil Burk, Mobileer Inc
+ * @see WhiteNoise
+ * @see RedNoise
+ * @see PinkNoise
+ */
+public class BrownNoise extends UnitGenerator implements UnitSource {
+    private PseudoRandom randomNum;
+    /** Increasing the damping will effectively increase the cutoff 
+     * frequency of a high pass filter that is used to block DC bias.
+     * Warning: setting this too close to zero can result in very large output values.
+     */
+    public UnitInputPort damping;
+    public UnitInputPort amplitude;
+    public UnitOutputPort output;
+    private double previous;
+
+    public BrownNoise() {
+        randomNum = new PseudoRandom();
+        addPort(damping = new UnitInputPort("Damping"));
+        damping.setup(0.0001, 0.01, 0.1);
+        addPort(amplitude = new UnitInputPort("Amplitude", UnitOscillator.DEFAULT_AMPLITUDE));
+        addPort(output = new UnitOutputPort("Output"));
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] amplitudes = amplitude.getValues();
+        double[] outputs = output.getValues();
+        double damper = 1.0 - damping.getValues()[0];
+
+        for (int i = start; i < limit; i++) {
+            double r = randomNum.nextRandomDouble() * amplitudes[i];
+            outputs[i] = previous = (damper * previous) + r;
+        }
+    }
+
+    @Override
+    public UnitOutputPort getOutput() {
+        return output;
+    }
+}
diff --git a/src/com/jsyn/unitgen/ExponentialRamp.java b/src/com/jsyn/unitgen/ExponentialRamp.java
index 4befbeb..36159b4 100644
--- a/src/com/jsyn/unitgen/ExponentialRamp.java
+++ b/src/com/jsyn/unitgen/ExponentialRamp.java
@@ -38,6 +38,7 @@ public class ExponentialRamp extends UnitFilter {
 
     public ExponentialRamp() {
         addPort(time = new UnitInputPort("Time"));
+        input.setup(0.0001, 1.0, 1.0);
         addPort(current = new UnitVariablePort("Current", 1.0));
     }