From e51bd49f87052d0706a016fab88d18ffef05b8b1 Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Sat, 8 Sep 2018 16:48:13 +0100
Subject: [PATCH] audio_core: Add audio stretcher
---
src/audio_core/CMakeLists.txt | 2 ++
src/audio_core/time_stretch.cpp | 64 +++++++++++++++++++++++++++++++++
src/audio_core/time_stretch.h | 35 ++++++++++++++++++
3 files changed, 101 insertions(+)
create mode 100644 src/audio_core/time_stretch.cpp
create mode 100644 src/audio_core/time_stretch.h
diff --git a/src/audio_core/CMakeLists.txt b/src/audio_core/CMakeLists.txt
index de5c291ceb..c381dbe1dc 100644
--- a/src/audio_core/CMakeLists.txt
+++ b/src/audio_core/CMakeLists.txt
@@ -17,6 +17,8 @@ add_library(audio_core STATIC
sink_stream.h
stream.cpp
stream.h
+ time_stretch.cpp
+ time_stretch.h
$<$<BOOL:${ENABLE_CUBEB}>:cubeb_sink.cpp cubeb_sink.h>
)
diff --git a/src/audio_core/time_stretch.cpp b/src/audio_core/time_stretch.cpp
new file mode 100644
index 0000000000..17e1283236
--- /dev/null
+++ b/src/audio_core/time_stretch.cpp
@@ -0,0 +1,64 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <algorithm>
+#include <cmath>
+#include <cstddef>
+#include "audio_core/time_stretch.h"
+#include "common/logging/log.h"
+
+namespace AudioCore {
+
+TimeStretcher::TimeStretcher(u32 sample_rate, u32 channel_count)
+ : m_sample_rate(sample_rate), m_channel_count(channel_count) {
+ m_sound_touch.setChannels(channel_count);
+ m_sound_touch.setSampleRate(sample_rate);
+ m_sound_touch.setPitch(1.0);
+ m_sound_touch.setTempo(1.0);
+}
+
+void TimeStretcher::Clear() {
+ m_sound_touch.clear();
+}
+
+size_t TimeStretcher::Process(const s16* in, size_t num_in, s16* out, size_t num_out) {
+ const double time_delta = static_cast<double>(num_out) / m_sample_rate; // seconds
+
+ // We were given actual_samples number of samples, and num_samples were requested from us.
+ double current_ratio = static_cast<double>(num_in) / static_cast<double>(num_out);
+
+ const double max_latency = 0.3; // seconds
+ const double max_backlog = m_sample_rate * max_latency / 1000.0 / m_stretch_ratio;
+ const double backlog_fullness = m_sound_touch.numSamples() / max_backlog;
+ if (backlog_fullness > 5.0) {
+ // Too many samples in backlog: Don't push anymore on
+ num_in = 0;
+ }
+
+ // We ideally want the backlog to be about 50% full.
+ // This gives some headroom both ways to prevent underflow and overflow.
+ // We tweak current_ratio to encourage this.
+ constexpr double tweak_time_scale = 0.05; // seconds
+ const double tweak_correction = (backlog_fullness - 0.5) * (time_delta / tweak_time_scale);
+ current_ratio *= std::pow(1.0 + 2.0 * tweak_correction, tweak_correction < 0 ? 3.0 : 1.0);
+
+ // This low-pass filter smoothes out variance in the calculated stretch ratio.
+ // The time-scale determines how responsive this filter is.
+ constexpr double lpf_time_scale = 2.0; // seconds
+ const double lpf_gain = 1.0 - std::exp(-time_delta / lpf_time_scale);
+ m_stretch_ratio += lpf_gain * (current_ratio - m_stretch_ratio);
+
+ // Place a lower limit of 10% speed. When a game boots up, there will be
+ // many silence samples. These do not need to be timestretched.
+ m_stretch_ratio = std::max(m_stretch_ratio, 0.1);
+ m_sound_touch.setTempo(m_stretch_ratio);
+
+ LOG_DEBUG(Audio, "Audio Stretching: samples:{}/{} ratio:{} backlog:{} gain: {}", num_in, num_out,
+ m_stretch_ratio, backlog_fullness, lpf_gain);
+
+ m_sound_touch.putSamples(in, num_in);
+ return m_sound_touch.receiveSamples(out, num_out);
+}
+
+} // namespace AudioCore
diff --git a/src/audio_core/time_stretch.h b/src/audio_core/time_stretch.h
new file mode 100644
index 0000000000..cdead34a24
--- /dev/null
+++ b/src/audio_core/time_stretch.h
@@ -0,0 +1,35 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <array>
+#include <cstddef>
+#include <SoundTouch.h>
+#include "common/common_types.h"
+
+namespace AudioCore {
+
+class TimeStretcher {
+public:
+ TimeStretcher(u32 sample_rate, u32 channel_count);
+
+ /// @param in Input sample buffer
+ /// @param num_in Number of input frames in `in`
+ /// @param out Output sample buffer
+ /// @param num_out Desired number of output frames in `out`
+ /// @returns Actual number of frames written to `out`
+ size_t Process(const s16* in, size_t num_in, s16* out, size_t num_out);
+
+ void Clear();
+
+private:
+ u32 m_sample_rate;
+ u32 m_channel_count;
+ std::array<s16, 2> m_last_stretched_sample = {};
+ soundtouch::SoundTouch m_sound_touch;
+ double m_stretch_ratio = 1.0;
+};
+
+} // namespace AudioCore
--
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