Helmholtz testing (no decay bug)

Core/SoundProcessor.cs

@@ -1,76 +1,34 @@
 using System;
-using FluidSim.Core;
 
 namespace FluidSim.Core
 {
-    /// <summary>
-    /// Synthesises far‑field exhaust sound using the monopole model
-    /// of Jones (1978).  The radiated pressure is proportional to the
-    /// time derivative of the mass flow at the pipe exit.
-    ///
-    /// Reference:
-    ///   Jones, A.D. (1978) "Noise characteristics and exhaust process
-    ///   gas dynamics of a small 2-stroke engine", PhD thesis, Univ. Adelaide.
-    /// </summary>
     public class SoundProcessor
     {
-        private readonly double dt;
-        private readonly double r;            // listener distance (m)
-        private readonly double scaleFactor;  // 1 / (4π r)  (free-field monopole)
+        private readonly float dt;
+        private readonly float scaleFactor;   // 1 / (4π r)
+        private float flowLP, prevMassFlowOut, smoothDMdt;
+        private readonly float lpAlpha, alpha;
 
-        // ---------- Mass‑flow derivative (identical to original) ----------
-        private double flowLP;
-        private readonly double lpAlpha;
-        private double prevMassFlowOut;
-        private double smoothDMdt;
-        private readonly double alpha;
+        public float Gain = 1f;
 
-        public float Gain { get; set; } = 1.0f;
-
-        /// <summary>
-        /// </summary>
-        /// <param name="sampleRate">Audio sample rate (Hz).</param>
-        /// <param name="listenerDistanceMeters">Listener distance (m).</param>
-        /// <param name="pipeDiameterMeters">Ignored in this model; kept for compatibility.</param>
-        public SoundProcessor(int sampleRate,
-                              double listenerDistanceMeters = 1.0,
-                              double pipeDiameterMeters = 0.0217)
+        public SoundProcessor(int sampleRate, float listenerDistance = 1f)
         {
-            dt = 1.0 / sampleRate;
-            r = listenerDistanceMeters;
-            scaleFactor = 1.0 / (4.0 * Math.PI * r);   // free‑field monopole
-
-            // ---- Smoothing time constants (unchanged) ----
-            double tau = 0.02;                     // 2 ms for derivative
-            alpha = Math.Exp(-dt / tau);
-
-            double tauLP = 0.00001;                   // 5 ms low‑pass on mass flow
-            lpAlpha = Math.Exp(-dt / tauLP);
+            dt = 1f / sampleRate;
+            scaleFactor = 1f / (4f * MathF.PI * listenerDistance);
+            float tau = 0.02f;
+            alpha = MathF.Exp(-dt / tau);
+            float tauLP = 0.005f;
+            lpAlpha = MathF.Exp(-dt / tauLP);
         }
 
-        /// <summary>
-        /// Process one sample.  The OpenEndLink provides the instantaneous
-        /// exit‑plane mass flow.
-        /// </summary>
-        public float Process(OpenEndLink openEnd)
+        public float Process(float massFlowOut)
         {
-            double flowOut = openEnd.LastMassFlowRate;   // kg/s, positive = leaving pipe
-
-            // Low‑pass the mass flow signal
-            flowLP = lpAlpha * flowLP + (1.0 - lpAlpha) * flowOut;
-
-            // Derivative of the smoothed mass flow
-            double rawDerivative = (flowLP - prevMassFlowOut) / dt;
+            flowLP = lpAlpha * flowLP + (1f - lpAlpha) * massFlowOut;
+            float rawDerivative = (flowLP - prevMassFlowOut) / dt;
             prevMassFlowOut = flowLP;
-
-            // Smooth the derivative
-            smoothDMdt = alpha * smoothDMdt + (1.0 - alpha) * rawDerivative;
-
-            // Far‑field monopole pressure (free‑field, Jones eq. 2.15 adapted)
-            double pressure = smoothDMdt * scaleFactor * Gain;
-
-            // Soft clip to ±1
-            return (float)pressure;
+            smoothDMdt = alpha * smoothDMdt + (1f - alpha) * rawDerivative;
+            float pressure = smoothDMdt * scaleFactor * Gain;
+            return MathF.Tanh(pressure);
         }
     }
 }