1 files changed, 62 insertions, 0 deletions

diff --git a/src/audio_core/algorithm/filter.h b/src/audio_core/algorithm/filter.h
new file mode 100644
index 000000000..a41beef98
--- /dev/null
+++ b/src/audio_core/algorithm/filter.h
@@ -0,0 +1,62 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <array>
+#include <vector>
+#include "common/common_types.h"
+
+namespace AudioCore {
+
+/// Digital biquad filter:
+///
+///          b0 + b1 z^-1 + b2 z^-2
+///  H(z) = ------------------------
+///          a0 + a1 z^-1 + b2 z^-2
+class Filter {
+public:
+    /// Creates a low-pass filter.
+    /// @param cutoff Determines the cutoff frequency. A value from 0.0 to 1.0.
+    /// @param Q Determines the quality factor of this filter.
+    static Filter LowPass(double cutoff, double Q = 0.7071);
+
+    /// Passthrough filter.
+    Filter();
+
+    Filter(double a0, double a1, double a2, double b0, double b1, double b2);
+
+    void Process(std::vector<s16>& signal);
+
+private:
+    static constexpr size_t channel_count = 2;
+
+    /// Coefficients are in normalized form (a0 = 1.0).
+    double a1, a2, b0, b1, b2;
+    /// Input History
+    std::array<std::array<double, channel_count>, 3> in;
+    /// Output History
+    std::array<std::array<double, channel_count>, 3> out;
+};
+
+/// Cascade filters to build up higher-order filters from lower-order ones.
+class CascadingFilter {
+public:
+    /// Creates a cascading low-pass filter.
+    /// @param cutoff Determines the cutoff frequency. A value from 0.0 to 1.0.
+    /// @param cascade_size Number of biquads in cascade.
+    static CascadingFilter LowPass(double cutoff, size_t cascade_size);
+
+    /// Passthrough.
+    CascadingFilter();
+
+    explicit CascadingFilter(std::vector<Filter> filters);
+
+    void Process(std::vector<s16>& signal);
+
+private:
+    std::vector<Filter> filters;
+};
+
+} // namespace AudioCore