From b125b8175fa46edd1bd33749b9c085dd9f5d6ee7 Mon Sep 17 00:00:00 2001
From: Axel Nana <axel.nana@aliens-group.com>
Date: Sun, 25 Aug 2024 04:51:20 +0100
Subject: [PATCH] fix(mixer): Improved dynamic sample rate conversion.

Signed-off-by: Axel Nana <axel.nana@aliens-group.com>
---
 .../Audio/Amplitude/DSP/AudioConverter.h      |  3 +++
 src/DSP/AudioConverter.cpp                    | 25 ++++++++++++++++---
 src/Mixer/Amplimix.cpp                        | 11 +++++---
 src/Mixer/Amplimix.h                          |  1 +
 4 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/include/SparkyStudios/Audio/Amplitude/DSP/AudioConverter.h b/include/SparkyStudios/Audio/Amplitude/DSP/AudioConverter.h
index f02de04f..342766c2 100644
--- a/include/SparkyStudios/Audio/Amplitude/DSP/AudioConverter.h
+++ b/include/SparkyStudios/Audio/Amplitude/DSP/AudioConverter.h
@@ -158,6 +158,9 @@ namespace SparkyStudios::Audio::Amplitude
         ChannelConversionMode _channelConversionMode;
 
         bool _needResampling;
+        bool _srcInitialized;
+
+        Settings _settings;
     };
 } // namespace SparkyStudios::Audio::Amplitude
 
diff --git a/src/DSP/AudioConverter.cpp b/src/DSP/AudioConverter.cpp
index a0b05167..d4359446 100644
--- a/src/DSP/AudioConverter.cpp
+++ b/src/DSP/AudioConverter.cpp
@@ -21,6 +21,8 @@ namespace SparkyStudios::Audio::Amplitude
     AudioConverter::AudioConverter()
         : _resampler(nullptr)
         , _channelConversionMode(kChannelConversionModeDisabled)
+        , _needResampling(false)
+        , _srcInitialized(false)
     {
         _resampler = Resampler::Construct("default");
         Reset();
@@ -42,8 +44,15 @@ namespace SparkyStudios::Audio::Amplitude
         else
             return false; // Unsupported channel conversion mode
 
-        _needResampling = settings.m_sourceChannelCount != settings.m_targetChannelCount;
-        _resampler->Initialize(settings.m_targetChannelCount, settings.m_sourceSampleRate, settings.m_targetSampleRate);
+        _needResampling = settings.m_sourceSampleRate != settings.m_targetSampleRate;
+
+        if (_needResampling)
+        {
+            _resampler->Initialize(settings.m_targetChannelCount, settings.m_sourceSampleRate, settings.m_targetSampleRate);
+            _srcInitialized = true;
+        }
+
+        _settings = settings;
 
         return true;
     }
@@ -78,7 +87,17 @@ namespace SparkyStudios::Audio::Amplitude
     void AudioConverter::SetSampleRate(AmUInt64 sourceSampleRate, AmUInt64 targetSampleRate)
     {
         _needResampling = sourceSampleRate != targetSampleRate;
-        _resampler->SetSampleRate(sourceSampleRate, targetSampleRate);
+
+        _settings.m_sourceSampleRate = sourceSampleRate;
+        _settings.m_targetSampleRate = targetSampleRate;
+
+        if (!_needResampling)
+            return;
+
+        if (_srcInitialized)
+            _resampler->SetSampleRate(sourceSampleRate, targetSampleRate);
+        else
+            _resampler->Initialize(_settings.m_targetChannelCount, sourceSampleRate, targetSampleRate);
     }
 
     AmUInt64 AudioConverter::GetRequiredInputFrameCount(AmUInt64 outputFrameCount) const
diff --git a/src/Mixer/Amplimix.cpp b/src/Mixer/Amplimix.cpp
index 8c34b438..130b6e18 100644
--- a/src/Mixer/Amplimix.cpp
+++ b/src/Mixer/Amplimix.cpp
@@ -17,7 +17,7 @@
 #include <Core/Engine.h>
 #include <Mixer/Amplimix.h>
 
-#define AMPLIMIX_STORE(A, C) std::atomic_store_explicit(A, C, std::memory_order_release)
+#define AMPLIMIX_STORE(A, C) std::atomic_store_explicit(A, (C), std::memory_order_release)
 #define AMPLIMIX_LOAD(A) std::atomic_load_explicit(A, std::memory_order_acquire)
 #define AMPLIMIX_CSWAP(A, E, C) std::atomic_compare_exchange_strong_explicit(A, E, C, std::memory_order_acq_rel, std::memory_order_acquire)
 
@@ -529,6 +529,10 @@ namespace SparkyStudios::Audio::Amplitude
             AMPLIMIX_STORE(&lay->userPlaySpeed, speed);
             // atomically set cursor to start position based on given argument
             AMPLIMIX_STORE(&lay->cursor, lay->start);
+            // store the base sample rate ratio for this source
+            AMPLIMIX_STORE(
+                &lay->baseSampleRateRatio,
+                static_cast<AmReal32>(sound->format.GetSampleRate()) / static_cast<AmReal32>(_device.mRequestedOutputSampleRate));
 
             // Initialize the converter
             lay->dataConverter = ampoolnew(MemoryPoolKind::Amplimix, AudioConverter);
@@ -1064,9 +1068,8 @@ namespace SparkyStudios::Audio::Amplitude
         {
             currentSpeed = AM_Lerp(currentSpeed, 0.75f, playSpeed);
 
-            const AmReal32 basePitch =
-                static_cast<AmReal32>(layer->snd->format.GetSampleRate()) / static_cast<AmReal32>(_device.mRequestedOutputSampleRate);
-            const AmReal32 sampleRateRatio = basePitch * currentSpeed;
+            const AmReal32 baseSampleRateRatio = AMPLIMIX_LOAD(&layer->baseSampleRateRatio);
+            const AmReal32 sampleRateRatio = baseSampleRateRatio * currentSpeed;
 
             AMPLIMIX_STORE(&layer->targetPlaySpeed, playSpeed);
             AMPLIMIX_STORE(&layer->sampleRateRatio, sampleRateRatio);
diff --git a/src/Mixer/Amplimix.h b/src/Mixer/Amplimix.h
index 0cfa48fb..1e1e2dbb 100644
--- a/src/Mixer/Amplimix.h
+++ b/src/Mixer/Amplimix.h
@@ -76,6 +76,7 @@ namespace SparkyStudios::Audio::Amplitude
         _Atomic(AmReal32) playSpeed; // current sound playback speed
         _Atomic(AmReal32) targetPlaySpeed; // computed (real) sound playback speed
         _Atomic(AmReal32) sampleRateRatio; // sample rate ratio
+        _Atomic(AmReal32) baseSampleRateRatio; // base sample rate ratio
 
         AudioConverter* dataConverter; // miniaudio resampler & channel converter