Add Exponential Moving Average Filter (TheAlgorithms#6075)

Shreya123714 · web-flow · commit 7b962a4a1d76 · 2024-11-01T08:38:27.000Z
diff --git a/src/main/java/com/thealgorithms/audiofilters/EMAFilter.java b/src/main/java/com/thealgorithms/audiofilters/EMAFilter.java
@@ -0,0 +1,48 @@
+package com.thealgorithms.audiofilters;
+
+/**
+ * Exponential Moving Average (EMA) Filter for smoothing audio signals.
+ *
+ * <p>This filter applies an exponential moving average to a sequence of audio
+ * signal values, making it useful for smoothing out rapid fluctuations.
+ * The smoothing factor (alpha) controls the degree of smoothing.
+ *
+ * <p>Based on the definition from
+ * <a href="https://en.wikipedia.org/wiki/Moving_average">Wikipedia link</a>.
+ */
+public class EMAFilter {
+    private final double alpha;
+    private double emaValue;
+    /**
+     * Constructs an EMA filter with a given smoothing factor.
+     *
+     * @param alpha Smoothing factor (0 < alpha <= 1)
+     * @throws IllegalArgumentException if alpha is not in (0, 1]
+     */
+    public EMAFilter(double alpha) {
+        if (alpha <= 0 || alpha > 1) {
+            throw new IllegalArgumentException("Alpha must be between 0 and 1.");
+        }
+        this.alpha = alpha;
+        this.emaValue = 0.0;
+    }
+    /**
+     * Applies the EMA filter to an audio signal array.
+     *
+     * @param audioSignal Array of audio samples to process
+     * @return Array of processed (smoothed) samples
+     */
+    public double[] apply(double[] audioSignal) {
+        if (audioSignal.length == 0) {
+            return new double[0];
+        }
+        double[] emaSignal = new double[audioSignal.length];
+        emaValue = audioSignal[0];
+        emaSignal[0] = emaValue;
+        for (int i = 1; i < audioSignal.length; i++) {
+            emaValue = alpha * audioSignal[i] + (1 - alpha) * emaValue;
+            emaSignal[i] = emaValue;
+        }
+        return emaSignal;
+    }
+}
diff --git a/src/test/java/com/thealgorithms/audiofilters/EMAFilterTest.java b/src/test/java/com/thealgorithms/audiofilters/EMAFilterTest.java
@@ -0,0 +1,41 @@
+package com.thealgorithms.audiofilters;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class EMAFilterTest {
+
+    @Test
+    public void testApplyBasicSignal() {
+        EMAFilter emaFilter = new EMAFilter(0.2);
+        double[] audioSignal = {0.1, 0.5, 0.8, 0.6, 0.3, 0.9, 0.4};
+        double[] expectedOutput = {0.1, 0.18, 0.304, 0.3632, 0.35056, 0.460448, 0.4483584};
+        double[] result = emaFilter.apply(audioSignal);
+        assertArrayEquals(expectedOutput, result, 1e-5);
+    }
+
+    @Test
+    public void testApplyEmptySignal() {
+        EMAFilter emaFilter = new EMAFilter(0.2);
+        double[] audioSignal = {};
+        double[] expectedOutput = {};
+        double[] result = emaFilter.apply(audioSignal);
+        assertArrayEquals(expectedOutput, result);
+    }
+
+    @Test
+    public void testAlphaBounds() {
+        EMAFilter emaFilterMin = new EMAFilter(0.01);
+        EMAFilter emaFilterMax = new EMAFilter(1.0);
+        double[] audioSignal = {1.0, 1.0, 1.0, 1.0};
+
+        // Minimal smoothing (alpha close to 0)
+        double[] resultMin = emaFilterMin.apply(audioSignal);
+        assertArrayEquals(audioSignal, resultMin, 1e-5);
+
+        // Maximum smoothing (alpha = 1, output should match input)
+        double[] resultMax = emaFilterMax.apply(audioSignal);
+        assertArrayEquals(audioSignal, resultMax, 1e-5);
+    }
+}
