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authorMerryMage <MerryMage@users.noreply.github.com>2018-08-12 20:32:39 +0200
committerMerryMage <MerryMage@users.noreply.github.com>2018-08-13 12:26:50 +0200
commit4b44b8b4fba5ddfe28e5c6bd418f48ba475eaa79 (patch)
treeaff40cf37d7946ebff6317f2f715f21075514ebb /src/audio_core/algorithm
parentaudio_core: Implement low-pass filter (diff)
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Diffstat (limited to 'src/audio_core/algorithm')
-rw-r--r--src/audio_core/algorithm/interpolate.cpp71
-rw-r--r--src/audio_core/algorithm/interpolate.h43
2 files changed, 114 insertions, 0 deletions
diff --git a/src/audio_core/algorithm/interpolate.cpp b/src/audio_core/algorithm/interpolate.cpp
new file mode 100644
index 000000000..11459821f
--- /dev/null
+++ b/src/audio_core/algorithm/interpolate.cpp
@@ -0,0 +1,71 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#define _USE_MATH_DEFINES
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+#include "audio_core/algorithm/interpolate.h"
+#include "common/common_types.h"
+#include "common/logging/log.h"
+
+namespace AudioCore {
+
+/// The Lanczos kernel
+static double Lanczos(size_t a, double x) {
+ if (x == 0.0)
+ return 1.0;
+ const double px = M_PI * x;
+ return a * std::sin(px) * std::sin(px / a) / (px * px);
+}
+
+std::vector<s16> Interpolate(InterpolationState& state, std::vector<s16> input, double ratio) {
+ if (input.size() < 2)
+ return {};
+
+ if (ratio <= 0) {
+ LOG_CRITICAL(Audio, "Nonsensical interpolation ratio {}", ratio);
+ ratio = 1.0;
+ }
+
+ if (ratio != state.current_ratio) {
+ const double cutoff_frequency = std::min(0.5 / ratio, 0.5 * ratio);
+ state.nyquist = CascadingFilter::LowPass(std::clamp(cutoff_frequency, 0.0, 0.4), 3);
+ state.current_ratio = ratio;
+ }
+ state.nyquist.Process(input);
+
+ constexpr size_t taps = InterpolationState::lanczos_taps;
+ const size_t num_frames = input.size() / 2;
+
+ std::vector<s16> output;
+ output.reserve(static_cast<size_t>(input.size() / ratio + 4));
+
+ double& pos = state.position;
+ auto& h = state.history;
+ for (size_t i = 0; i < num_frames; ++i) {
+ std::rotate(h.begin(), h.end() - 1, h.end());
+ h[0][0] = input[i * 2 + 0];
+ h[0][1] = input[i * 2 + 1];
+
+ while (pos <= 1.0) {
+ double l = 0.0;
+ double r = 0.0;
+ for (size_t j = 0; j < h.size(); j++) {
+ l += Lanczos(taps, pos + j - taps + 1) * h[j][0];
+ r += Lanczos(taps, pos + j - taps + 1) * h[j][1];
+ }
+ output.emplace_back(static_cast<s16>(std::clamp(l, -32768.0, 32767.0)));
+ output.emplace_back(static_cast<s16>(std::clamp(r, -32768.0, 32767.0)));
+
+ pos += ratio;
+ }
+ pos -= 1.0;
+ }
+
+ return output;
+}
+
+} // namespace AudioCore
diff --git a/src/audio_core/algorithm/interpolate.h b/src/audio_core/algorithm/interpolate.h
new file mode 100644
index 000000000..c79c2eef4
--- /dev/null
+++ b/src/audio_core/algorithm/interpolate.h
@@ -0,0 +1,43 @@
+// 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 "audio_core/algorithm/filter.h"
+#include "common/common_types.h"
+
+namespace AudioCore {
+
+struct InterpolationState {
+ static constexpr size_t lanczos_taps = 4;
+ static constexpr size_t history_size = lanczos_taps * 2 - 1;
+
+ double current_ratio = 0.0;
+ CascadingFilter nyquist;
+ std::array<std::array<s16, 2>, history_size> history = {};
+ double position = 0;
+};
+
+/// Interpolates input signal to produce output signal.
+/// @param input The signal to interpolate.
+/// @param ratio Interpolation ratio.
+/// ratio > 1.0 results in fewer output samples.
+/// ratio < 1.0 results in more output samples.
+/// @returns Output signal.
+std::vector<s16> Interpolate(InterpolationState& state, std::vector<s16> input, double ratio);
+
+/// Interpolates input signal to produce output signal.
+/// @param input The signal to interpolate.
+/// @param input_rate The sample rate of input.
+/// @param output_rate The desired sample rate of the output.
+/// @returns Output signal.
+inline std::vector<s16> Interpolate(InterpolationState& state, std::vector<s16> input,
+ u32 input_rate, u32 output_rate) {
+ const double ratio = static_cast<double>(input_rate) / static_cast<double>(output_rate);
+ return Interpolate(state, std::move(input), ratio);
+}
+
+} // namespace AudioCore