AudioCommon: extract AudioStretcher class for time-stretching

Source/Core/AudioCommon/AudioCommon.vcxproj

@@ -38,6 +38,7 @@
   <ItemGroup>
     <ClCompile Include="aldlist.cpp" />
     <ClCompile Include="AudioCommon.cpp" />
+    <ClCompile Include="AudioStretcher.cpp" />
     <ClCompile Include="CubebStream.cpp" />
     <ClCompile Include="CubebUtils.cpp" />
     <ClCompile Include="DPL2Decoder.cpp" />
@@ -54,6 +55,7 @@
     <ClInclude Include="aldlist.h" />
     <ClInclude Include="AlsaSoundStream.h" />
     <ClInclude Include="AudioCommon.h" />
+    <ClInclude Include="AudioStretcher.h" />
     <ClInclude Include="CoreAudioSoundStream.h" />
     <ClInclude Include="CubebStream.h" />
     <ClInclude Include="CubebUtils.h" />

Source/Core/AudioCommon/AudioCommon.vcxproj.filters

@@ -8,6 +8,7 @@
   <ItemGroup>
     <ClCompile Include="aldlist.cpp" />
     <ClCompile Include="AudioCommon.cpp" />
+    <ClCompile Include="AudioStretcher.cpp" />
     <ClCompile Include="CubebUtils.cpp" />
     <ClCompile Include="DPL2Decoder.cpp" />
     <ClCompile Include="Mixer.cpp" />
@@ -31,6 +32,7 @@
   <ItemGroup>
     <ClInclude Include="aldlist.h" />
     <ClInclude Include="AudioCommon.h" />
+    <ClInclude Include="AudioStretcher.h" />
     <ClInclude Include="CubebUtils.h" />
     <ClInclude Include="DPL2Decoder.h" />
     <ClInclude Include="Mixer.h" />

Source/Core/AudioCommon/AudioStretcher.cpp

@@ -0,0 +1,85 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include <cmath>
+
+#include "AudioCommon/AudioStretcher.h"
+#include "Common/Logging/Log.h"
+#include "Core/ConfigManager.h"
+
+namespace AudioCommon
+{
+AudioStretcher::AudioStretcher(unsigned int sample_rate) : m_sample_rate(sample_rate)
+{
+  m_sound_touch.setChannels(2);
+  m_sound_touch.setSampleRate(sample_rate);
+  m_sound_touch.setPitch(1.0);
+  m_sound_touch.setTempo(1.0);
+  m_sound_touch.setSetting(SETTING_USE_QUICKSEEK, 0);
+  m_sound_touch.setSetting(SETTING_SEQUENCE_MS, 62);
+  m_sound_touch.setSetting(SETTING_SEEKWINDOW_MS, 28);
+  m_sound_touch.setSetting(SETTING_OVERLAP_MS, 8);
+}
+
+void AudioStretcher::Clear()
+{
+  m_sound_touch.clear();
+}
+
+void AudioStretcher::StretchAudio(const short* in, unsigned int num_in, short* out,
+                                  unsigned int 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 = SConfig::GetInstance().m_audio_stretch_max_latency;
+  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 = 0.5;  // seconds
+  current_ratio *= 1.0 + 2.0 * (backlog_fullness - 0.5) * (time_delta / tweak_time_scale);
+
+  // 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 = 1.0;  // 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);
+
+  DEBUG_LOG(AUDIO, "Audio stretching: samples:%u/%u ratio:%f backlog:%f gain: %f", num_in, num_out,
+            m_stretch_ratio, backlog_fullness, lpf_gain);
+
+  m_sound_touch.putSamples(in, num_in);
+
+  const size_t samples_received = m_sound_touch.receiveSamples(out, num_out);
+
+  if (samples_received != 0)
+  {
+    m_last_stretched_sample[0] = out[samples_received * 2 - 2];
+    m_last_stretched_sample[1] = out[samples_received * 2 - 1];
+  }
+
+  // Perform padding if we've run out of samples.
+  for (size_t i = samples_received; i < num_out; i++)
+  {
+    out[i * 2 + 0] = m_last_stretched_sample[0];
+    out[i * 2 + 1] = m_last_stretched_sample[1];
+  }
+}
+
+}  // namespace AudioCommon

Source/Core/AudioCommon/AudioStretcher.h

@@ -0,0 +1,27 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <array>
+
+#include <soundtouch/SoundTouch.h>
+
+namespace AudioCommon
+{
+class AudioStretcher
+{
+public:
+  AudioStretcher(unsigned int sample_rate);
+  void StretchAudio(const short* in, unsigned int num_in, short* out, unsigned int num_out);
+  void Clear();
+
+private:
+  unsigned int m_sample_rate;
+  std::array<short, 2> m_last_stretched_sample = {};
+  soundtouch::SoundTouch m_sound_touch;
+  double m_stretch_ratio = 1.0;
+};
+
+}  // AudioCommon

Source/Core/AudioCommon/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(SRCS
   AudioCommon.cpp
+  AudioStretcher.cpp
   CubebStream.cpp
   CubebUtils.cpp
   DPL2Decoder.cpp

Source/Core/AudioCommon/Mixer.cpp

@@ -14,19 +14,10 @@
 #include "Common/Swap.h"
 #include "Core/ConfigManager.h"
 
-CMixer::CMixer(unsigned int BackendSampleRate) : m_sampleRate(BackendSampleRate)
+CMixer::CMixer(unsigned int BackendSampleRate)
+    : m_sampleRate(BackendSampleRate), m_stretcher(BackendSampleRate)
 {
   INFO_LOG(AUDIO_INTERFACE, "Mixer is initialized");
-
-  m_sound_touch.setChannels(2);
-  m_sound_touch.setSampleRate(BackendSampleRate);
-  m_sound_touch.setPitch(1.0);
-  m_sound_touch.setTempo(1.0);
-  m_sound_touch.setSetting(SETTING_USE_QUICKSEEK, 0);
-  m_sound_touch.setSetting(SETTING_SEQUENCE_MS, 62);
-  m_sound_touch.setSetting(SETTING_SEEKWINDOW_MS, 28);
-  m_sound_touch.setSetting(SETTING_OVERLAP_MS, 8);
-
   DPL2Reset();
 }
 
@@ -146,10 +137,10 @@ unsigned int CMixer::Mix(short* samples, unsigned int num_samples)
 
     if (!m_is_stretching)
     {
-      m_sound_touch.clear();
+      m_stretcher.Clear();
       m_is_stretching = true;
     }
-    StretchAudio(m_stretch_buffer.data(), available_samples, samples, num_samples);
+    m_stretcher.StretchAudio(m_stretch_buffer.data(), available_samples, samples, num_samples);
   }
   else
   {
@@ -181,60 +172,6 @@ unsigned int CMixer::MixSurround(float* samples, unsigned int num_samples)
   return available_samples;
 }
 
-void CMixer::StretchAudio(const short* in, unsigned int num_in, short* out, unsigned int num_out)
-{
-  const double time_delta = static_cast<double>(num_out) / m_sampleRate;  // 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 = SConfig::GetInstance().m_audio_stretch_max_latency;
-  const double max_backlog = m_sampleRate * 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 = 0.5;  // seconds
-  current_ratio *= 1.0 + 2.0 * (backlog_fullness - 0.5) * (time_delta / tweak_time_scale);
-
-  // 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 = 1.0;  // seconds
-  const double m_lpf_gain = 1.0 - std::exp(-time_delta / lpf_time_scale);
-  m_stretch_ratio += m_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);
-
-  DEBUG_LOG(AUDIO, "Audio stretching: samples:%u/%u ratio:%f backlog:%f gain: %f", num_in, num_out,
-            m_stretch_ratio, backlog_fullness, m_lpf_gain);
-
-  m_sound_touch.putSamples(in, num_in);
-
-  const size_t samples_received = m_sound_touch.receiveSamples(out, num_out);
-
-  if (samples_received != 0)
-  {
-    m_last_stretched_sample[0] = out[samples_received * 2 - 2];
-    m_last_stretched_sample[1] = out[samples_received * 2 - 1];
-  }
-
-  // Preform padding if we've run out of samples.
-  for (size_t i = samples_received; i < num_out; i++)
-  {
-    out[i * 2 + 0] = m_last_stretched_sample[0];
-    out[i * 2 + 1] = m_last_stretched_sample[1];
-  }
-}
-
 void CMixer::MixerFifo::PushSamples(const short* samples, unsigned int num_samples)
 {
   // Cache access in non-volatile variable

Source/Core/AudioCommon/Mixer.h

@@ -7,12 +7,10 @@
 #include <array>
 #include <atomic>
 
+#include "AudioCommon/AudioStretcher.h"
 #include "AudioCommon/WaveFile.h"
 #include "Common/CommonTypes.h"
 
-#include <soundtouch/STTypes.h>
-#include <soundtouch/SoundTouch.h>
-
 class CMixer final
 {
 public:
@@ -76,17 +74,13 @@ private:
     u32 m_frac = 0;
   };
 
-  void StretchAudio(const short* in, unsigned int num_in, short* out, unsigned int num_out);
-
   MixerFifo m_dma_mixer{this, 32000};
   MixerFifo m_streaming_mixer{this, 48000};
   MixerFifo m_wiimote_speaker_mixer{this, 3000};
   unsigned int m_sampleRate;
 
   bool m_is_stretching = false;
-  soundtouch::SoundTouch m_sound_touch;
+  AudioCommon::AudioStretcher m_stretcher;
-  double m_stretch_ratio = 1.0;
-  std::array<short, 2> m_last_stretched_sample = {};
   std::array<short, MAX_SAMPLES * 2> m_stretch_buffer;
   std::array<float, MAX_SAMPLES * 2> m_float_conversion_buffer;