1 files changed, 59 insertions, 0 deletions
diff --git a/src/3rdparty/resonance-audio/resonance_audio/dsp/mono_pole_filter.cc b/src/3rdparty/resonance-audio/resonance_audio/dsp/mono_pole_filter.cc
new file mode 100644
index 000000000..18c4625d5
--- /dev/null
+++ b/src/3rdparty/resonance-audio/resonance_audio/dsp/mono_pole_filter.cc
@@ -0,0 +1,59 @@
+/*
+Copyright 2018 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS-IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+#include "dsp/mono_pole_filter.h"
+
+#include <algorithm>
+
+#include "base/constants_and_types.h"
+
+
+namespace vraudio {
+
+MonoPoleFilter::MonoPoleFilter(float coefficient) : previous_output_(0.0f) {
+  SetCoefficient(coefficient);
+}
+
+void MonoPoleFilter::SetCoefficient(float coefficient) {
+  coefficient_ = std::max(std::min(coefficient, 1.0f), 0.0f);
+}
+
+bool MonoPoleFilter::Filter(const AudioBuffer::Channel& input,
+                            AudioBuffer::Channel* output) {
+
+  DCHECK(output);
+  const size_t num_frames = input.size();
+  DCHECK_EQ(num_frames, output->size());
+
+  // Do not perform processing if the coefficient is zero to avoid wasteful
+  // "all pass" cases.
+  if (coefficient_ < kEpsilonFloat) {
+    previous_output_ = input[num_frames - 1];
+    return false;
+  }
+
+  // The difference equation implemented here is as follows:
+  // y[n] = a * (y[n-1] - x[n]) + x[n]
+  // where y[n] is the output and x[n] is the input vector.
+  for (size_t frame = 0; frame < num_frames; ++frame) {
+    (*output)[frame] =
+        coefficient_ * (previous_output_ - input[frame]) + input[frame];
+    previous_output_ = (*output)[frame];
+  }
+  return true;
+}
+
+}  // namespace vraudio