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]>

2 files changed, 108 insertions, 0 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;
+    }
+}