From 1636106bbef14fa34d062681fff3c54d5581e202 Mon Sep 17 00:00:00 2001
From: Daniel Jones <daniel@jones.org.uk>
Date: Sun, 12 Nov 2023 21:51:34 +0000
Subject: [PATCH] Add DCFilter node

---
 .../signalflow/node/processors/filters/dc.h   | 26 +++++++++++
 source/include/signalflow/signalflow.h        |  1 +
 source/src/CMakeLists.txt                     |  1 +
 source/src/node/processors/filters/dc.cpp     | 45 +++++++++++++++++++
 source/src/python/nodes.cpp                   |  3 ++
 5 files changed, 76 insertions(+)
 create mode 100644 source/include/signalflow/node/processors/filters/dc.h
 create mode 100644 source/src/node/processors/filters/dc.cpp

diff --git a/source/include/signalflow/node/processors/filters/dc.h b/source/include/signalflow/node/processors/filters/dc.h
new file mode 100644
index 00000000..a8194fd2
--- /dev/null
+++ b/source/include/signalflow/node/processors/filters/dc.h
@@ -0,0 +1,26 @@
+#pragma once
+
+#include "signalflow/core/constants.h"
+#include "signalflow/node/node.h"
+
+namespace signalflow
+{
+/**--------------------------------------------------------------------------------*
+ * Remove DC offset.
+ *---------------------------------------------------------------------------------*/
+class DCFilter : public UnaryOpNode
+{
+public:
+    DCFilter(NodeRef input = 0.0);
+
+    virtual void process(Buffer &out, int num_frames) override;
+    virtual void alloc() override;
+
+private:
+    float R;
+    std::vector<float> previous_input;
+    std::vector<float> previous_output;
+};
+
+REGISTER(DCFilter, "dc-filter")
+}
diff --git a/source/include/signalflow/signalflow.h b/source/include/signalflow/signalflow.h
index 6aeece21..8a3d248f 100644
--- a/source/include/signalflow/signalflow.h
+++ b/source/include/signalflow/signalflow.h
@@ -126,6 +126,7 @@
 #include <signalflow/node/processors/dynamics/maximiser.h>
 #include <signalflow/node/processors/dynamics/rms.h>
 #include <signalflow/node/processors/filters/biquad.h>
+#include <signalflow/node/processors/filters/dc.h>
 #include <signalflow/node/processors/filters/eq.h>
 #include <signalflow/node/processors/filters/moog.h>
 #include <signalflow/node/processors/filters/svf.h>
diff --git a/source/src/CMakeLists.txt b/source/src/CMakeLists.txt
index fd0c902c..3efa7c3f 100644
--- a/source/src/CMakeLists.txt
+++ b/source/src/CMakeLists.txt
@@ -56,6 +56,7 @@ set(SRC ${SRC}
         ${CMAKE_CURRENT_SOURCE_DIR}/node/processors/filters/svf.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/node/processors/filters/eq.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/node/processors/filters/moog.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/node/processors/filters/dc.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/node/processors/panning/stereo-panner.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/node/processors/panning/stereo-balance.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/node/processors/panning/stereo-width.cpp
diff --git a/source/src/node/processors/filters/dc.cpp b/source/src/node/processors/filters/dc.cpp
new file mode 100644
index 00000000..20d5ff0b
--- /dev/null
+++ b/source/src/node/processors/filters/dc.cpp
@@ -0,0 +1,45 @@
+#include "signalflow/core/graph.h"
+#include "signalflow/node/processors/filters/dc.h"
+
+#include <stdlib.h>
+
+namespace signalflow
+{
+
+DCFilter::DCFilter(NodeRef input)
+    : UnaryOpNode(input)
+{
+    this->name = "dc-filter";
+
+    // "R" depends on sampling rate and the low frequency point. Do not set "R" to a fixed value
+    // (e.g. 0.99) if you don't know the sample rate. Instead set R to:
+    // (-3dB @ 40Hz): R = 1-(250/samplerate)
+    // (-3dB @ 30Hz): R = 1-(190/samplerate)
+    // (-3dB @ 20Hz): R = 1-(126/samplerate)
+    // this->R = 1.0 - (30.0 / this->get_graph()->get_sample_rate());
+
+    //    this->alloc();
+}
+
+void DCFilter::alloc()
+{
+    this->previous_input.resize(this->num_output_channels_allocated);
+    this->previous_output.resize(this->num_output_channels_allocated);
+}
+
+void DCFilter::process(Buffer &out, int num_frames)
+{
+    this->R = 1.0 - (30.0 / this->graph->get_sample_rate());
+    for (int channel = 0; channel < num_output_channels; channel++)
+    {
+        for (int frame = 0; frame < num_frames; frame++)
+        {
+            float output = this->input->out[channel][frame] - this->previous_input[channel] + R * this->previous_output[channel];
+            this->previous_input[channel] = this->input->out[channel][frame];
+            this->previous_output[channel] = output;
+            out[channel][frame] = output;
+        }
+    }
+}
+
+}
diff --git a/source/src/python/nodes.cpp b/source/src/python/nodes.cpp
index d8377dad..b2d93ac3 100644
--- a/source/src/python/nodes.cpp
+++ b/source/src/python/nodes.cpp
@@ -308,6 +308,9 @@ void init_python_nodes(py::module &m)
         .def(py::init<NodeRef, signalflow_filter_type_t, NodeRef, NodeRef, NodeRef>(), "input"_a = 0.0, "filter_type"_a = SIGNALFLOW_FILTER_TYPE_LOW_PASS, "cutoff"_a = 440, "resonance"_a = 0.0, "peak_gain"_a = 0.0)
         .def(py::init<NodeRef, std::string, NodeRef, NodeRef, NodeRef>(), "input"_a, "filter_type"_a, "cutoff"_a = 440, "resonance"_a = 0.0, "peak_gain"_a = 0.0);
 
+    py::class_<DCFilter, Node, NodeRefTemplate<DCFilter>>(m, "DCFilter", "Remove DC offset.")
+        .def(py::init<NodeRef>(), "input"_a = 0.0);
+
     py::class_<EQ, Node, NodeRefTemplate<EQ>>(m, "EQ", "Three-band EQ.")
         .def(py::init<NodeRef, NodeRef, NodeRef, NodeRef, NodeRef, NodeRef>(), "input"_a = 0.0, "low_gain"_a = 1.0, "mid_gain"_a = 1.0, "high_gain"_a = 1.0, "low_freq"_a = 500, "high_freq"_a = 5000);