Add PlateReverb, RoomReverb and MultiTapDelay units (#115)

PlateReverb is a simulation of a metal plate based on all-pass delays.

RoomReverb uses a MultiTapDelay for early reflections and a PlateReverb for diffusion.

Add a DSP package with utility classes used to build unit generators.

Add TuneReverb app with faders for experimenting and hearing reverb.

Add unit tests for SimpleDelay.

Co-authored-by: Phil Burk <[email protected]>

9 files changed, 817 insertions, 5 deletions

diff --git a/src/main/java/com/jsyn/dsp/AllPassDelay.java b/src/main/java/com/jsyn/dsp/AllPassDelay.java
new file mode 100644
index 0000000..4afea19
--- /dev/null
+++ b/src/main/java/com/jsyn/dsp/AllPassDelay.java
@@ -0,0 +1,37 @@
+/*
+ * Copyright 2022 Phil Burk
+ *
+ * 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.dsp;
+
+public class AllPassDelay {
+    private float[] mBuffer;
+    private int mCursor;
+    private float mCoefficient = 0.65f;
+
+    public AllPassDelay(int length, float coefficient) {
+        mBuffer = new float[length];
+        mCoefficient = coefficient;
+    }
+
+    public float process(float input) {
+        float z = mBuffer[mCursor];
+        float x = input - (z * mCoefficient);
+        mBuffer[mCursor] = x;
+        mCursor++;
+        if (mCursor >= mBuffer.length) mCursor = 0;
+        return z + (x * mCoefficient);
+    }
+}
diff --git a/src/main/java/com/jsyn/dsp/SimpleDelay.java b/src/main/java/com/jsyn/dsp/SimpleDelay.java
new file mode 100644
index 0000000..b4818c1
--- /dev/null
+++ b/src/main/java/com/jsyn/dsp/SimpleDelay.java
@@ -0,0 +1,71 @@
+/*
+ * Copyright 2022 Phil Burk
+ *
+ * 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.dsp;
+
+/**
+ * Delay line based on a circular buffer.
+ */
+public class SimpleDelay {
+    private float[] mBuffer;
+    private int mCursor;
+
+    public SimpleDelay(int length) {
+        mBuffer = new float[length];
+    }
+
+    /**
+     * Read a value from the delay line.
+     * @param position positive delay in frames
+     * @return delayed value
+     */
+    public float read(int position) {
+        int index = mCursor - position;
+        if (index < 0) {
+            index += mBuffer.length;
+        }
+        return mBuffer[index];
+    }
+
+    /**
+     * Write a new value to the head of the delay line.
+     * This does not advance the cursor.
+     * @param input sample value
+     */
+    public void write(float input) {
+        mBuffer[mCursor] = input;
+    }
+
+    /**
+     * Advance the cursor position. Wrap around in a circle.
+     */
+    public void advance() {
+        mCursor++;
+        if (mCursor >= mBuffer.length) mCursor = 0;
+    }
+
+    /**
+     * Add a new value and return the oldest value in the delay line.
+     * @param input sample value
+     * @return oldest value
+     */
+    public float process(float input) {
+        float output = mBuffer[mCursor];
+        write(input);
+        advance();
+        return output;
+    }
+}
diff --git a/src/main/java/com/jsyn/engine/SynthesisEngine.java b/src/main/java/com/jsyn/engine/SynthesisEngine.java
index 34fffbe..6d985b4 100644
--- a/src/main/java/com/jsyn/engine/SynthesisEngine.java
+++ b/src/main/java/com/jsyn/engine/SynthesisEngine.java
@@ -224,8 +224,11 @@ public class SynthesisEngine implements Synthesizer {
 
         setupAudioBuffers(numInputChannels, numOutputChannels);
 
-        logger.info("Pure Java JSyn from www.softsynth.com, rate = " + frameRate + ", "
-                + (useRealTime ? "RT" : "NON-RealTime") + ", " + JSyn.VERSION_TEXT);
+        if (false) {
+            logger.info("Pure Java JSyn from www.softsynth.com, rate = " + frameRate
+                    + ", " + (useRealTime ? "RT" : "NON-RealTime")
+                    + ", " + JSyn.VERSION_TEXT);
+        }
 
         inverseNyquist = 2.0 / frameRate;
 
diff --git a/src/main/java/com/jsyn/swing/PortControllerFactory.java b/src/main/java/com/jsyn/swing/PortControllerFactory.java
index a73d047..0f98ea6 100644
--- a/src/main/java/com/jsyn/swing/PortControllerFactory.java
+++ b/src/main/java/com/jsyn/swing/PortControllerFactory.java
@@ -4,9 +4,9 @@
  * 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.
@@ -19,11 +19,12 @@ package com.jsyn.swing;
 import javax.swing.event.ChangeEvent;
 import javax.swing.event.ChangeListener;
 
+import com.jsyn.ports.SettablePort;
 import com.jsyn.ports.UnitInputPort;
 
 /**
  * Factory class for making various controllers for JSyn ports.
- * 
+ *
  * @author Phil Burk (C) 2010 Mobileer Inc
  */
 public class PortControllerFactory {
diff --git a/src/main/java/com/jsyn/unitgen/MultiTapDelay.java b/src/main/java/com/jsyn/unitgen/MultiTapDelay.java
new file mode 100644
index 0000000..17db94a
--- /dev/null
+++ b/src/main/java/com/jsyn/unitgen/MultiTapDelay.java
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2023 Phil Burk
+ *
+ * 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.dsp.SimpleDelay;
+import com.jsyn.ports.UnitInputPort;
+
+/**
+ * Delay with multiple read positions and associated gains.
+ */
+public class MultiTapDelay extends UnitFilter {
+
+    /** Pre-delay time in milliseconds. */
+    public UnitInputPort preDelayMillis;
+    private final int mMaxPreDelayFrames;
+    private SimpleDelay mPreDelay;
+    private SimpleDelay mDelay;
+    private final int[] mPositions;
+    private final float[] mGains;
+
+    private int mPreDelayFrames = 0;
+
+    /**
+     * Construct a delay line with specified taps.
+     * The allocated size of the delay line will be the maximum position plus the maxPreDelayFrames.
+     * @param positions delay index, eg. 172 for Z(n-172)
+     * @param gains multiplier for the corresponding position
+     * @param maxPreDelayFrames extra allocated frames for pre-delay before the taps
+     */
+    public MultiTapDelay(final int[] positions,
+                final float[] gains,
+                final int maxPreDelayFrames) {
+        mPositions = positions;
+        mGains = gains;
+
+        preDelayMillis = new UnitInputPort("PreDelayMillis");
+        double maxMillis = maxPreDelayFrames * 1000.0 / 44100; // TODO handle unknown frame rate better
+        preDelayMillis.setup(0.0, Math.min(10.0, maxMillis), maxMillis);
+        addPort(preDelayMillis);
+        mMaxPreDelayFrames = Math.max(1, maxPreDelayFrames);
+        mPreDelay = new SimpleDelay(maxPreDelayFrames);
+
+        int maxPosition = 0;
+        for (int position : positions) {
+            maxPosition = Math.max(maxPosition, position);
+        }
+        mDelay = new SimpleDelay(maxPosition);
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] inputs = input.getValues();
+        double[] outputs = output.getValues();
+
+        double preDelayMS = preDelayMillis.getValues()[0];
+        int preDelayFrames = (int)(preDelayMS * 0.001 * getFrameRate());
+        preDelayFrames = Math.max(1, Math.min(mMaxPreDelayFrames, preDelayFrames));
+
+        for (int i = start; i < limit; i++) {
+            mPreDelay.write((float) inputs[i]);
+            mDelay.write(mPreDelay.read(preDelayFrames));
+            mPreDelay.advance();
+            double sum = 0.0;
+            for (int tap = 0; tap < mPositions.length; tap++) {
+                sum += mDelay.read(mPositions[tap]) * mGains[tap];
+            }
+            mDelay.advance();
+            outputs[i] = sum; // mix taps
+        }
+    }
+}
diff --git a/src/main/java/com/jsyn/unitgen/Pan.java b/src/main/java/com/jsyn/unitgen/Pan.java
index bc90984..77b2694 100644
--- a/src/main/java/com/jsyn/unitgen/Pan.java
+++ b/src/main/java/com/jsyn/unitgen/Pan.java
@@ -41,6 +41,7 @@ public class Pan extends UnitGenerator {
     public Pan() {
         addPort(input = new UnitInputPort("Input"));
         addPort(pan = new UnitInputPort("Pan"));
+        pan.setup(-1.0, 0.0, 1.0);
         addPort(output = new UnitOutputPort(2, "Output"));
     }
 
diff --git a/src/main/java/com/jsyn/unitgen/PlateReverb.java b/src/main/java/com/jsyn/unitgen/PlateReverb.java
new file mode 100644
index 0000000..88eef33
--- /dev/null
+++ b/src/main/java/com/jsyn/unitgen/PlateReverb.java
@@ -0,0 +1,366 @@
+/*
+ * Copyright 2022 Phil Burk
+ *
+ * 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.dsp.AllPassDelay;
+import com.jsyn.dsp.SimpleDelay;
+import com.jsyn.ports.UnitInputPort;
+import com.jsyn.ports.UnitOutputPort;
+import com.jsyn.util.PseudoRandom;
+
+/**
+ * Simple reverberation effect based on a "figure eight"
+ * network of all-pass filters and delays.
+ *
+ * This reverb  does not have a pre-delay or early reflections.
+ * It can be used as the "tail" of a more complex reverb that
+ * adds those functions.
+ *
+ * The algorithm is based on
+ * "Effect Design Part 1: Reverberator and Other Filters"
+ * by Jon Dattorro, CCRMA, Stanford University 1996
+ *
+ * @see InterpolatingDelay
+ */
+
+public class PlateReverb extends UnitGenerator {
+
+    /**
+     * Mono input.
+     */
+    public UnitInputPort input;
+
+    /**
+     * Approximate time in seconds to decay by -60 dB.
+     */
+    public UnitInputPort time;
+
+    /**
+     * Damping factor for the feedback filters.
+     * Must be between 0.0 and 1.0. Default is 0.5.
+     */
+    public UnitInputPort damping;
+
+    /**
+     * Stereo output.
+     */
+    public UnitOutputPort output;
+
+    private static final double MAX_DECAY = 0.98;
+    // These default values are based on table-1 of the paper by Jon Dattorro.
+    private static final float DECAY_DIFFUSION_1 = 0.70f;
+    private static final float DECAY_DIFFUSION_2 = 0.50f;
+    private static final float INPUT_DIFFUSION_1 = 0.75f;
+    private static final float INPUT_DIFFUSION_2 = 0.625f;
+    private static final float DAMPING = 0.5f; // Must match default comment above for damping port.
+    private static final float BANDWIDTH = 0.99995f;
+
+    private static class FastSineOscillator {
+        private float mPhaseIncrement = 0.0001f;
+        private float mPhaseDelta = mPhaseIncrement;
+        private float mPhase; // ranges from -PI/2 to PI/2
+        private static final float PHASE_LIMIT = (float) Math.PI * 0.5f;
+
+        void setFrequency(float frequency, float sampleRate) {
+            mPhaseIncrement = (float) (frequency * Math.PI / sampleRate);
+        }
+
+        float generate() {
+            // Generate a triangle wave
+            mPhase += mPhaseDelta;
+            if (mPhase > PHASE_LIMIT) {
+                mPhase = PHASE_LIMIT - (mPhase - PHASE_LIMIT);
+                mPhaseDelta = -mPhaseIncrement; // reverse direction
+            } else if (mPhase < -PHASE_LIMIT) {
+                mPhase = -PHASE_LIMIT + (-PHASE_LIMIT - mPhase);
+                mPhaseDelta = mPhaseIncrement; // reverse direction
+            }
+
+            // Factorial constants so code is easier to read.
+            final float IF3 = 1.0f / (2 * 3);
+            final float IF5 = IF3 / (4 * 5);
+            final float IF7 = IF5 / (6 * 7);
+            final float IF9 = IF7 / (8 * 9);
+            final float IF11 = IF9 / (10 * 11);
+
+            float x = mPhase;
+            float x2 = (x * x);
+            /* Taylor expansion factored into multiply-adds */
+            // TODO use fewer factors cuz just modulation
+            return x
+                    * (x2 * (x2 * (x2 * (x2 * ((x2 * (-IF11)) + IF9) - IF7) + IF5) - IF3) + 1);
+        }
+    }
+
+    private static class RandomModulator {
+        private PseudoRandom randomNum = new PseudoRandom();;
+        protected float prevNoise, currNoise;
+        private float mPhase;
+        private float mPhaseIncrement;
+
+        void setFrequency(float frequency, float sampleRate) {
+            mPhaseIncrement = frequency / sampleRate;
+        }
+
+        // Generate ramps between random points between -1.0 and +1.0.
+        public float generate() {
+            mPhase += mPhaseIncrement;
+
+            // calculate new random value whenever phase passes 1.0
+            if (mPhase > 1.0) {
+                prevNoise = currNoise;
+                currNoise = (float) randomNum.nextRandomDouble();
+                // reset phase for interpolation
+                mPhase -= 1.0;
+            }
+
+            // interpolate current
+            return prevNoise + (mPhase * (currNoise - prevNoise));
+        }
+    }
+
+    /**
+     * Allpass delay modulated by a random ramp.
+     */
+    private static class VariableAllPassDelay {
+        RandomModulator mModulator = new RandomModulator();
+        private float[] mBuffer;
+        private int mLength;
+        private int mCursor;
+        private int mModulationDepth;
+        private float mCoefficient = 0.65f;
+
+        VariableAllPassDelay(int length, float coefficient) {
+            mLength = length;
+            mBuffer = new float[2 * length];
+            mCoefficient = coefficient;
+            setModulationDepth(40);
+        }
+
+        void setModulationDepth(int depthInFrames) {
+            mModulationDepth = Math.min(depthInFrames, mLength / 3);
+        }
+
+        void setFrequency(float frequency, float sampleRate) {
+            mModulator.setFrequency(frequency, sampleRate);
+        }
+
+        private float process(float input) {
+            int readCursor = mCursor - mLength;
+            readCursor += (int)(mModulator.generate() * mModulationDepth);
+            if (readCursor < 0) readCursor += mBuffer.length;
+
+            float z = mBuffer[readCursor];
+
+            float x = input - (z * mCoefficient );
+            mBuffer[mCursor] = x;
+            mCursor++;
+            if (mCursor >= mBuffer.length) mCursor = 0;
+            return z + (x * mCoefficient);
+        }
+    }
+
+    // y = x*c + y*(1-c)
+    private static class OnePoleLowPassFilter {
+        private float mDelay;
+        private float mCoefficient;
+
+        OnePoleLowPassFilter(float coefficient) {
+            mCoefficient = coefficient;
+        }
+
+        private float process(float input) {
+            float output = (input * mCoefficient)
+                    + (mDelay * (1.0f - mCoefficient));
+            mDelay = output;
+            return output;
+        }
+
+        public void setCoefficient(float coefficient) {
+            mCoefficient = coefficient;
+        }
+    }
+
+    // One side of the figure eight.
+    private class ReverbSide {
+        VariableAllPassDelay variableDelay;
+        OnePoleLowPassFilter mLowPass = new OnePoleLowPassFilter(1.0f - DAMPING);
+        SimpleDelay mDelay1;
+        AllPassDelay mAllPassDelay;
+        SimpleDelay  mDelay2;
+        private float outputScaler = 0.6f;
+        private float mOutput;
+
+        ReverbSide(int d1, int d2, int d3, int d4) {
+            // This all pass reverses the signs.
+            variableDelay = new VariableAllPassDelay(d1, 0.0f - DECAY_DIFFUSION_1);
+            mDelay1 = new SimpleDelay(d2);
+            mAllPassDelay = new AllPassDelay(d3, DECAY_DIFFUSION_2);
+            mDelay2 = new SimpleDelay(d4);
+        }
+
+        public void setFrequency(float frequency, float sampleRate) {
+            variableDelay.setFrequency(frequency, sampleRate);
+        }
+
+        private float process(float input) {
+            float temp = variableDelay.process(input);
+            mOutput = temp;
+            temp = mDelay1.process(temp);
+            mOutput -= temp;
+            temp = mLowPass.process(temp);
+            temp *= mDecay;
+            temp = mAllPassDelay.process(temp);
+            mOutput += temp;
+            temp = mDelay2.process(temp);
+            temp *= mDecay;
+            mOutput -= temp;
+            return temp;
+        }
+
+        private float getOutput() {
+            return mOutput * outputScaler;
+        }
+
+        public void setDamping(float damping) {
+            mLowPass.setCoefficient(1.0f - damping);
+        }
+    }
+
+    private float mDecay;
+    private float mLeftFeedback;
+    private float mRightFeedback;
+    private double mSize = 1.0;
+    private double mPreviousTime = -1.0;
+
+    private OnePoleLowPassFilter mBandwidthLowPass = new OnePoleLowPassFilter(BANDWIDTH);
+    private AllPassDelay mDiffusion1 = new AllPassDelay(142, INPUT_DIFFUSION_1);
+    private AllPassDelay mDiffusion2 = new AllPassDelay(107, INPUT_DIFFUSION_1);
+    private AllPassDelay mDiffusion3 = new AllPassDelay(379, INPUT_DIFFUSION_2);
+    private AllPassDelay mDiffusion4 = new AllPassDelay(277, INPUT_DIFFUSION_2);
+    private ReverbSide mLeftSide;
+    private ReverbSide mRightSide;
+
+
+    /**
+     * Create a PlateReverb with a default size of 1.0.
+     */
+    public PlateReverb() {
+        this(1.0);
+    }
+
+    /**
+     * This reverb uses multiple delay lines. The size parameter
+     * scales the allocated size. A value of 1.0 is the default.
+     * At low values the reverb will sound more metallic, like a comb filter.
+     * At larger values it will sound more echoey.
+     *
+     * The size value will be clipped between 0.05 and 5.0.
+     *
+     * @param size adjust internal delay sizes
+     */
+    public PlateReverb(double size) {
+
+        addPort(input = new UnitInputPort("Input"));
+
+        size = Math.max(0.05, Math.min(5.0, size));
+        mSize = size;
+        addPort(time = new UnitInputPort("Time"));
+        time.setup(0.01, 2.0, 30.0);
+        addPort(damping = new UnitInputPort("Damping"));
+        damping.setup(0.0001, DAMPING, 1.0);
+
+        addPort(output = new UnitOutputPort(2,"Output"));
+
+        // delay line sizes
+        // These are from the original paper.
+        // int[] zs = {142, 107, 379, 277, // diffusion
+        //     672, 4453, 1800, 3720, // left
+        //     908, 4217, 2656, 3163}; // right
+        // These are aligned to nearby primes.
+        int[] zs = {149, 107, 379, 277, // diffusion
+            677, 4453, 1801, 3727, // left
+            911, 4217, 2657, 3169}; // right
+
+        mDiffusion1 = new AllPassDelay((int)(zs[0] * size), INPUT_DIFFUSION_1);
+        mDiffusion2 = new AllPassDelay((int)(zs[1] * size), INPUT_DIFFUSION_1);
+        mDiffusion3 = new AllPassDelay((int)(zs[2] * size), INPUT_DIFFUSION_2);
+        mDiffusion4 = new AllPassDelay((int)(zs[3] * size), INPUT_DIFFUSION_2);
+        mLeftSide = new ReverbSide((int)(zs[4] * size), (int)(zs[5] * size),
+                (int)(zs[6] * size), (int)(zs[7] * size));
+        mRightSide = new ReverbSide((int)(zs[8] * size), (int)(zs[9] * size),
+                (int)(zs[10] * size), (int)(zs[11] * size));
+        mLeftSide.setFrequency(0.7f, 44100.0f); // TODO use actual sample rate
+         mRightSide.setFrequency(1.2f, 44100.0f); // TODO use actual sample rate
+    }
+
+    // Unfortunately, Java does not have a simple duple support.
+    // So we return void and then get teh two values from the left and
+    // right sides.
+    private void process(float x) {
+        x = mBandwidthLowPass.process(x);
+        x = mDiffusion1.process(x);
+        x = mDiffusion2.process(x);
+        x = mDiffusion3.process(x);
+        x = mDiffusion4.process(x);
+        // left side of the figure eight uses right side feedback
+        float leftSum = x + mRightFeedback;
+        mLeftFeedback = mLeftSide.process(leftSum);
+        // right side of the figure eight uses left side feedback
+        float rightSum = x + mLeftFeedback;
+        mRightFeedback = mRightSide.process(rightSum);
+    }
+
+
+    // This equation was derived from measuring the actual RT60 as a function
+    // of size and decay.
+    // time = size * (0.52 - (4.7 *  Math.log(1.0001 - (decay * decay))));
+    // time/size = 0.52 - (4.7 *  Math.log(1.0001 - (decay * decay)))
+    // time/size - 0.52 = -4.7 *  Math.log(1.0001 - (decay * decay))
+    // (0.52 - (time/size))/ 4.7 = Math.log(1.0001 - (decay * decay))
+    // Math.exp((0.52 - (time/size))/ 4.7) = 1.0001 - (decay * decay)
+    // 1.001 - Math.exp((0.52 - (time/size))/ 4.7) = decay * decay
+    // decay = Math.sqrt(1.001 - Math.exp((0.52 - (time/size))/ 4.7))
+    private double convertTimeToDecay(double size, double time) {
+        double exponent = (0.52 - (time / size))/ 4.7;
+        double square = 1.001 - Math.exp(exponent); // TODO optimize
+        double decay = Math.sqrt(Math.max(0.0, square)); // avoid sqrt(negative)
+        return Math.min(MAX_DECAY, decay);
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] inputs = input.getValues();
+        double[] leftOutputs = output.getValues(0);
+        double[] rightOutputs = output.getValues(1);
+
+        double timeValue = (float) time.getValues()[0];
+        if (timeValue != mPreviousTime) {
+            mDecay = (float) convertTimeToDecay(mSize, timeValue);
+            mPreviousTime = timeValue;
+        }
+        float dampingValue = (float) damping.getValues()[0];
+        mLeftSide.setDamping(dampingValue);
+        mRightSide.setDamping(dampingValue);
+        for (int i = start; i < limit; i++) {
+            process((float) inputs[i]);
+            leftOutputs[i] = mLeftSide.getOutput();
+            rightOutputs[i] = mRightSide.getOutput();
+        }
+    }
+
+}
diff --git a/src/main/java/com/jsyn/unitgen/RoomReverb.java b/src/main/java/com/jsyn/unitgen/RoomReverb.java
new file mode 100644
index 0000000..eec1a5e
--- /dev/null
+++ b/src/main/java/com/jsyn/unitgen/RoomReverb.java
@@ -0,0 +1,175 @@
+/*
+ * Copyright 2022 Phil Burk
+ *
+ * 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;
+
+/**
+ * Simulate reverberation in a room using a MultiTapDelay to model the early reflections
+ * and a PlateReverb to provide diffusion.
+ *
+ * @author (C) 2022 Phil Burk, Mobileer Inc
+ * @see MultiTapDelay
+ * @see PlateReverb
+ */
+public class RoomReverb extends Circuit {
+    private static final double SIZE_SCALER_MIN = 0.05;
+    private static final double SIZE_SCALER_MAX = 5.0;
+    private static final int[] kPositions = {
+        10, 197, 401,
+        521, 733, 1117,
+        1481, 2731, 4177,
+        6073, 7927, 9463};
+    // Gains based on attenuation in air after a pre-delay.
+    // See spreadsheet MiscSynthCalculations
+    private static final float[] kGains = {
+        0.1840f, -0.1543f, -0.1311f,
+        0.1205f, -0.1054f, -0.0859f,
+        -0.0731f, -0.0484f, 0.0347f,
+        0.0254f, 0.0201f, -0.0171f};
+
+    /**
+     * Mono input.
+     */
+    public UnitInputPort input;
+
+    /** Pre-delay time in milliseconds. */
+    public UnitInputPort preDelayMillis;
+
+    /**
+     * Approximate time in seconds to decay by -60 dB.
+     */
+    public UnitInputPort time;
+
+    /**
+     * Damping factor for the feedback filters.
+     * Must be <= 1.0. Default is 0.5.
+     */
+    public UnitInputPort damping;
+
+    /**
+     * Amount of multi-tap delay in the output mix.
+     * Must be between 0.0 and 1.0.
+     */
+    public UnitInputPort multiTap;
+
+    /**
+     * Amount of diffusion in the output mix.
+     * Must be between 0.0 and 1.0.
+     */
+    public UnitInputPort diffusion;
+
+    /**
+     * Stereo output.
+     */
+    public UnitOutputPort output;
+
+    private final PlateReverb mPlateReverb;
+    private final MultiTapDelay mMultiTapDelay;
+    private final RoomReverbMixer mRoomReverbMixer;
+
+    /**
+     * Construct a RoomReverb with a default size of 1.0.
+     */
+    public RoomReverb() {
+        this(1.0);
+    }
+
+    /**
+     * The size parameter scales the allocated size.
+     * A value of 1.0 is the default.
+     * At low values the reverb will sound more metallic, like a comb filter.
+     * At larger values it will have longer echos.
+     *
+     * The size value will be clipped between 0.05 and 5.0.
+     *
+     * @param size adjust internal delay sizes
+     */
+    public RoomReverb(double size) {
+        size = Math.max(SIZE_SCALER_MIN, Math.min(SIZE_SCALER_MAX, size));
+
+        int[] positions = new int[kPositions.length];
+        for (int tap = 0; tap < kPositions.length; tap++) {
+            positions[tap] = (int) (kPositions[tap] * size);
+        }
+        add(mMultiTapDelay = new MultiTapDelay(positions, kGains,
+            (int)(4000 * size) /* preDelayFrames */)); // roughly 80 msec max
+        add(mPlateReverb = new PlateReverb(1.0));
+        add(mRoomReverbMixer = new RoomReverbMixer());
+
+        mMultiTapDelay.output.connect(mPlateReverb.input);
+        mMultiTapDelay.output.connect(mRoomReverbMixer.multiTapInput);
+        mPlateReverb.output.connect(0, mRoomReverbMixer.diffusionInput, 0);
+        mPlateReverb.output.connect(1, mRoomReverbMixer.diffusionInput, 1);
+
+        // Assign ports
+        input = mMultiTapDelay.input;
+        addPort(input);
+        preDelayMillis = mMultiTapDelay.preDelayMillis;
+        addPort(preDelayMillis);
+        time = mPlateReverb.time;
+        addPort(time);
+        damping = mPlateReverb.damping;
+        addPort(damping);
+        multiTap = mRoomReverbMixer.multiTapGain;
+        addPort(multiTap);
+        diffusion = mRoomReverbMixer.diffusionGain;
+        addPort(diffusion);
+        output = mRoomReverbMixer.output;
+        addPort(output);
+    }
+
+    // Custom mixer for room reverb.
+    // This is faster than multiple small unit generators.
+    static class RoomReverbMixer extends UnitGenerator {
+        public UnitInputPort multiTapInput;
+        public UnitInputPort diffusionInput;
+
+        public UnitInputPort multiTapGain;
+        public UnitInputPort diffusionGain;
+        public UnitOutputPort output;
+
+        /* Define Unit Ports used by connect() and set(). */
+        public RoomReverbMixer() {
+            addPort(multiTapInput = new UnitInputPort("MultiTapInput"));
+            addPort(diffusionInput = new UnitInputPort(2,"DiffusionInput"));
+            addPort(multiTapGain = new UnitInputPort("MultiTap"));
+            addPort(diffusionGain = new UnitInputPort(2,"Diffusion"));
+            multiTapGain.setup(0.0, 1.0, 1.0);
+            diffusionGain.setup(0.0, 1.0, 1.0);
+            addPort(output = new UnitOutputPort(2,"Output"));
+        }
+
+        @Override
+        public void generate(int start, int limit) {
+            double[] multiTapInputs = multiTapInput.getValues();
+            double[] diffusionInputs0 = diffusionInput.getValues(0);
+            double[] diffusionInputs1 = diffusionInput.getValues(1);
+            double multiTapGainValue = multiTapGain.getValues()[start];
+            double diffusionGainValue = diffusionGain.getValues()[start];
+            double[] outputs0 = output.getValues(0);
+            double[] outputs1 = output.getValues(1);
+
+            for (int i = start; i < limit; i++) {
+                double multiTapScaled = multiTapInputs[i] * multiTapGainValue;
+                outputs0[i] = multiTapScaled + (diffusionInputs0[i] * diffusionGainValue);
+                outputs1[i] = multiTapScaled + (diffusionInputs1[i] * diffusionGainValue);
+            }
+        }
+    }
+}
diff --git a/src/test/java/com/jsyn/dsp/TestSimpleDelay.java b/src/test/java/com/jsyn/dsp/TestSimpleDelay.java
new file mode 100644
index 0000000..400b6d7
--- /dev/null
+++ b/src/test/java/com/jsyn/dsp/TestSimpleDelay.java
@@ -0,0 +1,73 @@
+/*
+ * Copyright 2009 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.dsp;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import com.jsyn.engine.SynthesisEngine;
+import com.jsyn.unitgen.Add;
+import com.jsyn.unitgen.Compare;
+import com.jsyn.unitgen.Divide;
+import com.jsyn.unitgen.Maximum;
+import com.jsyn.unitgen.Minimum;
+import com.jsyn.unitgen.Multiply;
+import com.jsyn.unitgen.MultiplyAdd;
+import com.jsyn.unitgen.PitchToFrequency;
+import com.jsyn.unitgen.PowerOfTwo;
+import com.jsyn.unitgen.Subtract;
+import com.jsyn.unitgen.UnitBinaryOperator;
+import com.softsynth.math.AudioMath;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Phil Burk, (C) 2009 Mobileer Inc
+ */
+public class TestSimpleDelay {
+
+    @Test
+    public void testProcess() {
+        SimpleDelay delay = new SimpleDelay(3);
+        assertEquals(0.0f, delay.process(0.0f), 0.00001, "Start with zero");
+        assertEquals(0.0f, delay.process(0.7f), 0.00001, "Add an impulse");
+        assertEquals(0.0f, delay.process(0.0f), 0.00001, "Waiting 0");
+        assertEquals(0.0f, delay.process(0.0f), 0.00001, "Waiting 1");
+        assertEquals(0.7f, delay.process(0.0f), 0.00001, "Got it.");
+    }
+
+    @Test
+    public void testAddRead() {
+        SimpleDelay delay = new SimpleDelay(3);
+        assertEquals(0.0f, delay.read(0), 0.00001, "read[0]");
+        assertEquals(0.0f, delay.read(1), 0.00001, "read[1]");
+        assertEquals(0.0f, delay.read(2), 0.00001, "read[2]");
+        delay.write(1.23f);
+        assertEquals(1.23f, delay.read(0), 0.00001, "w0 read[0]");
+        assertEquals(0.0f, delay.read(1), 0.00001, "w0 read[1]");
+        assertEquals(0.0f, delay.read(2), 0.00001, "w0 read[2]");
+        delay.advance();
+        delay.write(0.0f);
+        assertEquals(0.0f, delay.read(0), 0.00001, "w1 read[0]");
+        assertEquals(1.23f, delay.read(1), 0.00001, "w1 read[1]");
+        assertEquals(0.0f, delay.read(2), 0.00001, "w1 read[2]");
+        delay.advance();
+        delay.write(0.567f);
+        assertEquals(0.567f, delay.read(0), 0.00001, "w1 read[0]");
+        assertEquals(0.0f, delay.read(1), 0.00001, "w1 read[1]");
+        assertEquals(1.23f, delay.read(2), 0.00001, "w1 read[2]");
+    }
+}