From 98a69bf0cb95296fc4afd3d943a63db73a1ae22a Mon Sep 17 00:00:00 2001
From: Dominik Kaiser
Date: Fri, 26 Sep 2025 11:55:28 +0200
Subject: Implement all-pass filter

---
 src/DSP/AllPassFilter.cpp | 24 ++++++++++++++++++++++++
 src/DSP/AllPassFilter.h   | 16 ++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 src/DSP/AllPassFilter.cpp
 create mode 100644 src/DSP/AllPassFilter.h

diff --git a/src/DSP/AllPassFilter.cpp b/src/DSP/AllPassFilter.cpp
new file mode 100644
index 0000000..e90bff7
--- /dev/null
+++ b/src/DSP/AllPassFilter.cpp
@@ -0,0 +1,24 @@
+#include "AllPassFilter.h"
+
+void AllPassFilter::prepare(double sampleRate, int samplesPerBlock) {
+  int maxDelayTimeMs = 100;
+  int maxDelaySamples = static_cast<int>(sampleRate * maxDelayTimeMs / 1000.0);
+
+  delayBuffer.resize(maxDelaySamples, 0.0f);
+  delayInSamples = static_cast<int>(sampleRate * 0.02);
+  delayBufferWritePos = 0;
+}
+
+void AllPassFilter::process(float* sample) {
+  int delayBufferLength = (int)delayBuffer.size();
+  int delayReadPos =
+      (delayBufferWritePos - delayInSamples + delayBufferLength) %
+      delayBufferLength;
+  float xn = *sample;
+  float delayedSample = delayBuffer[delayReadPos];
+  float yn = -gain * xn + delayedSample;  
+
+  delayBuffer[delayBufferWritePos] = xn + gain * yn;
+  *sample = yn;
+  delayBufferWritePos = (delayBufferWritePos + 1) % delayBufferLength;
+}
diff --git a/src/DSP/AllPassFilter.h b/src/DSP/AllPassFilter.h
new file mode 100644
index 0000000..be35129
--- /dev/null
+++ b/src/DSP/AllPassFilter.h
@@ -0,0 +1,16 @@
+#pragma once
+
+#include <juce_audio_processors/juce_audio_processors.h>
+
+class AllPassFilter {
+public:
+  void prepare(double sampleRate, int samplesPerBlock);
+  void reset();
+  void process(float *sample);
+
+private:
+  std::vector<float> delayBuffer;
+  int delayBufferWritePos = 0;
+  int delayInSamples = 0;
+  float gain = 0.7f;
+};
-- 
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