diff --git a/src/jsMain/kotlin/nl/astraeus/vst/ADSR.kt b/src/jsMain/kotlin/nl/astraeus/vst/ADSR.kt
new file mode 100644
index 0000000..ed6bd25
--- /dev/null
+++ b/src/jsMain/kotlin/nl/astraeus/vst/ADSR.kt
@@ -0,0 +1,43 @@
+package nl.astraeus.vst
+
+object ADSR {
+
+  fun calculate(
+    attack: Double,
+    decay: Double,
+    sustain: Double,
+    release: Double,
+    startTime: Double,
+    time: Double,
+    releaseTime: Double? = null
+  ): Double {
+    val attackTime = startTime + attack
+    val decayTime = attackTime + decay
+
+    return when {
+      time < startTime -> {
+        0.0
+      }
+
+      time < attackTime -> {
+        (time - startTime) / attack
+      }
+
+      time < decayTime -> {
+        sustain + ((1 - (((time - attackTime) / decay))) * (1 - sustain))
+      }
+
+      releaseTime == null -> {
+        sustain
+      }
+
+      time < releaseTime + release -> {
+        (1 - ((time - releaseTime) / release)) * sustain
+      }
+
+      else -> {
+        0.0
+      }
+    }
+  }
+}
\ No newline at end of file
diff --git a/src/jsMain/kotlin/nl/astraeus/vst/Externals.kt b/src/jsMain/kotlin/nl/astraeus/vst/Externals.kt
index ccbe28c..e6f01af 100644
--- a/src/jsMain/kotlin/nl/astraeus/vst/Externals.kt
+++ b/src/jsMain/kotlin/nl/astraeus/vst/Externals.kt
@@ -40,4 +40,4 @@ abstract external class AudioWorkletProcessor {
 
 external fun registerProcessor(name: String, processorCtor: JsClass<*>)
 external val sampleRate: Int
-external val currentTime: Double
+external val currentTime: Double
\ No newline at end of file