General testing
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namespace FluidSim.Core
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{
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/// <summary>
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/// Mixes multiple audio samples and applies a soft‑clipping tanh.
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/// </summary>
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public static class SoundProcessor
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{
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/// <summary>Overall gain applied after mixing (before tanh).</summary>
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public static float MasterGain { get; set; } = 0.01f;
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using System;
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/// <summary>
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/// Mixes an array of raw audio samples and returns a single sample in [‑1, 1].
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/// </summary>
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public static float MixAndClip(params float[] samples)
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namespace FluidSim.Core
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{
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public class SoundProcessor
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{
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// Monopole state
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private double lastMassFlow = 0.0;
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private double dt;
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// Resonant band‑pass filter (second‑order)
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private double b0, b1, b2, a1, a2;
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private double x1 = 0, x2 = 0, y1 = 0, y2 = 0;
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private double pipeLength;
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// Reverb (outdoor)
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private float[] delayLine;
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private int writeIndex;
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private float feedback = 0.50f;
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private float lowpassCoeff = 0.70f;
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private float lastFeedbackSample = 0f;
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// Turbulence (pink noise scaled by U³)
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private PinkNoiseGenerator pinkNoise;
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private float turbulenceGain = 0.05f;
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private double pipeArea;
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private double ambientPressure = 101325.0;
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// Gains
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private float masterGain = 0.0005f;
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private float pressureGain = 0.12f;
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public SoundProcessor(int sampleRate, double pipeLengthMeters, double pipeDiameterMeters = 0.04, float reverbTimeMs = 200.0f)
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{
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dt = 1.0 / sampleRate;
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pipeLength = pipeLengthMeters;
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pipeArea = Math.PI * Math.Pow(pipeDiameterMeters / 2.0, 2.0);
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// Design resonant filter at pipe fundamental frequency
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double c = 340.0;
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double f0 = c / (4.0 * pipeLength);
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double Q = 15.0;
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double omega = 2.0 * Math.PI * f0;
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double alpha = Math.Sin(omega * dt) / (2.0 * Q);
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double norm = 1.0 / (1.0 + alpha);
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b0 = alpha * norm;
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b1 = 0.0;
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b2 = -alpha * norm;
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a1 = -2.0 * Math.Cos(omega * dt) * norm;
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a2 = (1.0 - alpha) * norm;
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// Reverb delay line
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int delaySamples = (int)(sampleRate * reverbTimeMs / 1000.0);
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delayLine = new float[delaySamples];
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writeIndex = 0;
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pinkNoise = new PinkNoiseGenerator();
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}
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public float MasterGain
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{
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get => masterGain;
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set => masterGain = value;
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}
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public float PressureGain
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{
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get => pressureGain;
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set => pressureGain = value;
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}
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public float TurbulenceGain
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{
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get => turbulenceGain;
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set => turbulenceGain = value;
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}
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public void SetAmbientPressure(double p) => ambientPressure = p;
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public void SetPipeDiameter(double diameterMeters) => pipeArea = Math.PI * Math.Pow(diameterMeters / 2.0, 2.0);
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public float Process(float massFlow, float pipeEndPressure)
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{
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// 1. Monopole source: d(mdot)/dt
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double derivative = (massFlow - lastMassFlow) / dt;
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lastMassFlow = massFlow;
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float monopole = (float)(derivative * masterGain);
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// 2. Pressure difference (low‑frequency component)
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float pressureDiff = (float)((pipeEndPressure - ambientPressure) / ambientPressure) * pressureGain;
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float mixed = monopole + pressureDiff;
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// DO NOT clamp here – let the filter and final clamp handle dynamics
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// 3. Resonant band‑pass filter
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double y = b0 * mixed + b1 * x1 + b2 * x2 - a1 * y1 - a2 * y2;
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x2 = x1; x1 = mixed;
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y2 = y1; y1 = y;
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float resonant = (float)Math.Clamp(y, -1f, 1f);
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// 4. Turbulence noise: amplitude ∝ U³ (empirical for low speeds)
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double velocity = massFlow / (pipeArea * 1.225);
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double Uref = 100.0;
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double turbulenceAmp = Math.Pow(Math.Abs(velocity) / Uref, 3.0);
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float pink = pinkNoise.Next() * turbulenceGain * (float)turbulenceAmp;
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resonant += pink;
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resonant = Math.Clamp(resonant, -1f, 1f);
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// 5. Outdoor reverb
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float delayed = delayLine[writeIndex];
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float filteredDelay = delayed * lowpassCoeff + lastFeedbackSample * (1f - lowpassCoeff);
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lastFeedbackSample = filteredDelay;
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float wet = delayed + filteredDelay * feedback;
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delayLine[writeIndex] = resonant + filteredDelay * feedback;
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writeIndex = (writeIndex + 1) % delayLine.Length;
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// 6. Dry/wet mix
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float output = resonant * 0.7f + wet * 0.3f;
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output = Math.Clamp(output, -1f, 1f);
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return output;
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}
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}
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internal class PinkNoiseGenerator
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{
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private readonly Random random = new Random();
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private readonly float[] whiteNoise = new float[7];
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private int currentIndex = 0;
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public PinkNoiseGenerator()
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{
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for (int i = 0; i < 7; i++)
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whiteNoise[i] = (float)(random.NextDouble() * 2.0 - 1.0);
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}
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public float Next()
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{
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whiteNoise[0] = (float)(random.NextDouble() * 2.0 - 1.0);
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currentIndex = (currentIndex + 1) & 0x7F;
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int updateMask = 0;
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int temp = currentIndex;
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for (int i = 0; i < 7; i++)
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{
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if ((temp & 1) == 0)
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updateMask |= (1 << i);
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temp >>= 1;
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}
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for (int i = 1; i < 7; i++)
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if ((updateMask & (1 << i)) != 0)
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whiteNoise[i] = (float)(random.NextDouble() * 2.0 - 1.0);
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float sum = 0f;
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foreach (float s in samples)
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sum += s;
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sum *= MasterGain;
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return sum;
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for (int i = 0; i < 7; i++) sum += whiteNoise[i];
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return sum / 3.5f;
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}
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}
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}
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