Add N-order IIR Filter

DIRECTORY.md

@@ -3,6 +3,8 @@
 ## Src
  * Main
  * Kotlin
+ * Audio Filters
+ * [IIRFilter](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/audio_filters/IIRFilter.kt)
  * Dynamic Programming
  * [Palindromepartitioning](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/dynamic_programming/PalindromePartitioning.kt)
  * Dynamicprogramming
@@ -38,6 +40,8 @@
  * [Quicksort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/QuickSort.kt)
  * [Selectionsort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/SelectionSort.kt)
  * Test
+ * Audio Filters
+ * [IIRFilterTest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/audio_filters/IIRFilterTest.kt)
  * Dynamic Programming
  * [Palindromepartitioningtest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/dynamic_programming/PalindromePartitioningTest.kt)
  * Dynamicprogramming

src/main/kotlin/audio_filters/IIRFilter.kt

@@ -0,0 +1,62 @@
+package audio_filters
+
+/**
+ * Implement N-order IIR Filter using 1st form
+ * Assumes inputs are normalized to [-1, 1]
+ *
+ * @param order order of the IIR Filter
+ */
+class IIRFilter(val order: Int) {
+ private val coeffsA = MutableList(order+1) { if (it == 0) 1.0 else 0.0 }
+ private val coeffsB = MutableList(order+1) { if (it == 0) 1.0 else 0.0 }
+ private val historyX = MutableList(order) { 0.0 }
+ private val historyY = MutableList(order) { 0.0 }
+
+ /**
+ * Process a single sample
+ *
+ * @param sample Sample to process
+ * @return processed sample
+ */
+ fun process(sample: Double): Double {
+ var result = 0.0
+
+ for (i in 1..order) {
+ result += coeffsB[i] * historyX[i-1] - coeffsA[i] * historyY[i-1]
+ }
+
+ result = (result + coeffsB[0] * sample) / coeffsA[0]
+
+ for (i in 1 until order) {
+ historyX[i] = historyX[i-1]
+ historyY[i] = historyY[i-1]
+ }
+
+ historyX[0] = sample
+ historyY[0] = result
+
+ return result
+ }
+
+ /**
+ * Set the A/B coefficients, where B is the numerator and A is the denominator
+ */
+ fun setCoeffs(coeffsA: List<Double>, coeffsB: List<Double>) {
+ if (coeffsA.size != order+1) {
+ throw IllegalArgumentException("Expected coeffsA to have ${order+1} values for $order-order IIR filter, got ${coeffsA.size}")
+ }
+
+ if (coeffsA[0] == 0.0) {
+ throw IllegalArgumentException("coeffsA[0] cannot be 0.0!")
+ }
+
+ if (coeffsB.size != order+1) {
+ throw IllegalArgumentException("Expected coeffsA to have ${order+1} values for $order-order IIR filter, got ${coeffsB.size}")
+ }
+
+ for (i in 0..order) {
+ this.coeffsA[i] = coeffsA[i]
+ this.coeffsB[i] = coeffsB[i]
+ }
+ }
+}

src/test/kotlin/audio_filters/IIRFilterTest.kt

@@ -0,0 +1,31 @@
+package audio_filters
+
+import org.junit.Test
+
+class IIRFilterTest {
+ @Test
+ fun iirFilterTestDefault() {
+ // Default behavior is to just return the sample
+ val filter = IIRFilter(10)
+ val sample = 0.5
+ assert(filter.process(sample) == sample)
+ }
+
+ @Test
+ fun iirFilterTestLowPass() {
+ // Butterworth low-pass filter with Fc=10_000
+ val filter = IIRFilter(2)
+ filter.setCoeffs(
+ listOf(1.0, -0.3075651627667613, 0.18834053593286307),
+ listOf(0.22019384329152544, 0.4403876865830509, 0.22019384329152544)
+ )
+
+ val samples = listOf(0.5, 1.0, -0.3)
+ val expected = listOf(0.11009692164576272, 0.47424966420914927, 0.6095534171786035)
+
+ for (i in samples.indices) {
+ val result = filter.process(samples[i])
+ assert(result == expected[i]) { "Expected ${expected[i]}, got $result" }
+ }
+ }
+}