From 56300f2928a4eb982cf686f9e920d6e1e3b59356 Mon Sep 17 00:00:00 2001 From: MerryMage Date: Sun, 12 Aug 2018 19:32:16 +0100 Subject: [PATCH] audio_core: Implement low-pass filter --- src/audio_core/CMakeLists.txt | 6 ++- src/audio_core/algorithm/filter.cpp | 79 +++++++++++++++++++++++++++++ src/audio_core/algorithm/filter.h | 62 ++++++++++++++++++++++ 3 files changed, 145 insertions(+), 2 deletions(-) create mode 100644 src/audio_core/algorithm/filter.cpp create mode 100644 src/audio_core/algorithm/filter.h diff --git a/src/audio_core/CMakeLists.txt b/src/audio_core/CMakeLists.txt index ec71524a3b..92322f59bc 100644 --- a/src/audio_core/CMakeLists.txt +++ b/src/audio_core/CMakeLists.txt @@ -1,4 +1,6 @@ add_library(audio_core STATIC + algorithm/filter.cpp + algorithm/filter.h audio_out.cpp audio_out.h audio_renderer.cpp @@ -7,12 +9,12 @@ add_library(audio_core STATIC codec.cpp codec.h null_sink.h - stream.cpp - stream.h sink.h sink_details.cpp sink_details.h sink_stream.h + stream.cpp + stream.h $<$:cubeb_sink.cpp cubeb_sink.h> ) diff --git a/src/audio_core/algorithm/filter.cpp b/src/audio_core/algorithm/filter.cpp new file mode 100644 index 0000000000..403b8503ff --- /dev/null +++ b/src/audio_core/algorithm/filter.cpp @@ -0,0 +1,79 @@ +// Copyright 2018 yuzu Emulator Project +// Licensed under GPLv2 or any later version +// Refer to the license.txt file included. + +#define _USE_MATH_DEFINES + +#include +#include +#include +#include +#include "audio_core/algorithm/filter.h" +#include "common/common_types.h" + +namespace AudioCore { + +Filter Filter::LowPass(double cutoff, double Q) { + const double w0 = 2.0 * M_PI * cutoff; + const double sin_w0 = std::sin(w0); + const double cos_w0 = std::cos(w0); + const double alpha = sin_w0 / (2 * Q); + + const double a0 = 1 + alpha; + const double a1 = -2.0 * cos_w0; + const double a2 = 1 - alpha; + const double b0 = 0.5 * (1 - cos_w0); + const double b1 = 1.0 * (1 - cos_w0); + const double b2 = 0.5 * (1 - cos_w0); + + return {a0, a1, a2, b0, b1, b2}; +} + +Filter::Filter() : Filter(1.0, 0.0, 0.0, 1.0, 0.0, 0.0) {} + +Filter::Filter(double a0, double a1, double a2, double b0, double b1, double b2) + : a1(a1 / a0), a2(a2 / a0), b0(b0 / a0), b1(b1 / a0), b2(b2 / a0) {} + +void Filter::Process(std::vector& signal) { + const size_t num_frames = signal.size() / 2; + for (size_t i = 0; i < num_frames; i++) { + std::rotate(in.begin(), in.end() - 1, in.end()); + std::rotate(out.begin(), out.end() - 1, out.end()); + + for (size_t ch = 0; ch < channel_count; ch++) { + in[0][ch] = signal[i * channel_count + ch]; + + out[0][ch] = b0 * in[0][ch] + b1 * in[1][ch] + b2 * in[2][ch] - a1 * out[1][ch] - + a2 * out[2][ch]; + + signal[i * 2 + ch] = std::clamp(out[0][ch], -32768.0, 32767.0); + } + } +} + +/// Calculates the appropriate Q for each biquad in a cascading filter. +/// @param total_count The total number of biquads to be cascaded. +/// @param index 0-index of the biquad to calculate the Q value for. +static double CascadingBiquadQ(size_t total_count, size_t index) { + const double pole = M_PI * (2 * index + 1) / (4.0 * total_count); + return 1.0 / (2.0 * std::cos(pole)); +} + +CascadingFilter CascadingFilter::LowPass(double cutoff, size_t cascade_size) { + std::vector cascade(cascade_size); + for (size_t i = 0; i < cascade_size; i++) { + cascade[i] = Filter::LowPass(cutoff, CascadingBiquadQ(cascade_size, i)); + } + return CascadingFilter{std::move(cascade)}; +} + +CascadingFilter::CascadingFilter() = default; +CascadingFilter::CascadingFilter(std::vector filters) : filters(std::move(filters)) {} + +void CascadingFilter::Process(std::vector& signal) { + for (auto& filter : filters) { + filter.Process(signal); + } +} + +} // namespace AudioCore diff --git a/src/audio_core/algorithm/filter.h b/src/audio_core/algorithm/filter.h new file mode 100644 index 0000000000..a41beef98b --- /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 +#include +#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& 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, 3> in; + /// Output History + std::array, 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 filters); + + void Process(std::vector& signal); + +private: + std::vector filters; +}; + +} // namespace AudioCore