Add Look Ahead to Audio Filter

Util/Audio/Filter/Gain.cs

@@ -18,5 +18,7 @@ namespace ADOFAIRenderer.Util.Audio.Filter
         }
 
         public void Reset() { }
+
+        public double Latency => 0.0;
     }
 }

Util/Audio/Filter/HardClip.cs

@@ -27,5 +27,7 @@ namespace ADOFAIRenderer.Util.Audio.Filter
         }
 
         public void Reset() { }
+
+        public double Latency => 0.0;
     }
 }

Util/Audio/Filter/IAudioFilter.cs

@@ -10,5 +10,7 @@ namespace ADOFAIRenderer.Util.Audio.Filter
         void ProcessBlock(Span<float> buffer);
         
         void Reset();
+
+        double Latency { get; }
     }
 }

Util/Audio/Filter/RMSCompressor.cs

@@ -12,6 +12,8 @@ namespace ADOFAIRenderer.Util.Audio.Filter
         private float _releaseTime = 0.100f; // in seconds
         private float _kneeDb = 5f; // in dB
         private float _rmsWindowTime = 0.030f; // in seconds
+        private float _lookAheadTime; // in seconds
+        private int _lookAheadSamples;
 
         private int _sampleRate = 44100;
         private int _channels = 2;
@@ -23,6 +25,20 @@ namespace ADOFAIRenderer.Util.Audio.Filter
         // Per-channel state
         private float[] _rmsState = Array.Empty<float>(); // running mean-square (MS) state
         private float[] _gainState = Array.Empty<float>(); // smoothed gain reduction in dB
+        private float[][] _delayBuffers = Array.Empty<float[]>(); // circular delay buffers
+        private int[] _delayWriteIndices = Array.Empty<int>();
+
+        public float LookAheadTime
+        {
+            get => _lookAheadTime;
+            set
+            {
+                _lookAheadTime = Math.Max(0f, Math.Min(1.0f, value));
+                UpdateLookAheadSettings();
+            }
+        }
+
+        public double Latency => _lookAheadTime;
 
         public float ThresholdDb
         {
@@ -80,6 +96,7 @@ namespace ADOFAIRenderer.Util.Audio.Filter
             UpdateAttackCoef();
             UpdateReleaseCoef();
             UpdateRmsCoef();
+            UpdateLookAheadSettings();
 
             _rmsState = new float[channels];
             _gainState = new float[channels];
@@ -87,6 +104,26 @@ namespace ADOFAIRenderer.Util.Audio.Filter
             Reset();
         }
 
+        private void UpdateLookAheadSettings()
+        {
+            _lookAheadSamples = (int)Math.Round(_sampleRate * _lookAheadTime);
+            ReallocateDelayBuffers();
+        }
+
+        private void ReallocateDelayBuffers()
+        {
+            if (_channels <= 0) return;
+
+            _delayBuffers = new float[_channels][];
+            _delayWriteIndices = new int[_channels];
+
+            for (int i = 0; i < _channels; i++)
+            {
+                _delayBuffers[i] = _lookAheadSamples > 0 ? new float[_lookAheadSamples] : Array.Empty<float>();
+                _delayWriteIndices[i] = 0;
+            }
+        }
+
         private void UpdateAttackCoef()
         {
             _attackCoef = (float)Math.Exp(-1.0 / (_sampleRate * _attackTime));
@@ -155,6 +192,16 @@ namespace ADOFAIRenderer.Util.Audio.Filter
             // Convert back to linear gain multiplier
             float linearGain = (float)Math.Pow(10.0, currentGain / 20.0);
 
+            if (_lookAheadSamples > 0 && _delayBuffers.Length > channel && _delayBuffers[channel].Length > 0)
+            {
+                var buffer = _delayBuffers[channel];
+                int writeIdx = _delayWriteIndices[channel];
+                float delayedSample = buffer[writeIdx];
+                buffer[writeIdx] = sample;
+                _delayWriteIndices[channel] = (writeIdx + 1) % _lookAheadSamples;
+                return delayedSample * linearGain;
+            }
+
             return sample * linearGain;
         }
 
@@ -171,6 +218,12 @@ namespace ADOFAIRenderer.Util.Audio.Filter
         {
             Array.Clear(_rmsState, 0, _rmsState.Length);
             Array.Clear(_gainState, 0, _gainState.Length);
+            
+            for (int i = 0; i < _delayBuffers.Length; i++)
+            {
+                Array.Clear(_delayBuffers[i], 0, _delayBuffers[i].Length);
+            }
+            Array.Clear(_delayWriteIndices, 0, _delayWriteIndices.Length);
         }
     }
 }

Util/Audio/OfflineAudioMixer.cs

@@ -98,6 +98,7 @@ namespace ADOFAIRenderer.Util.Audio
 
         // Clip Cache
         private readonly AudioClipCache _clipCache = new();
+        private bool _isPrimed;
 
         public OfflineAudioMixer(int targetChannels, int targetSampleRate)
         {
@@ -113,6 +114,16 @@ namespace ADOFAIRenderer.Util.Audio
             rmsCompressor.Initialize(_targetSampleRate, _targetChannels);
             _filters.AddLast(rmsCompressor);
             
+            var limiter = new RMSCompressor
+            {
+                ThresholdDb = 0, Ratio = float.PositiveInfinity,
+                AttackTime = 0f, ReleaseTime = 0.05f,
+                KneeDb = 10, RmsWindowTime = 0.02f,
+                LookAheadTime = 0.01f
+            };
+            limiter.Initialize(_targetSampleRate, _targetChannels);
+            _filters.AddLast(limiter);
+            
             var hardClip = new HardClip();
             hardClip.Initialize(_targetSampleRate, _targetChannels);
             _filters.AddLast(hardClip);
@@ -173,11 +184,10 @@ namespace ADOFAIRenderer.Util.Audio
                     Pitch = pitch
                 };
                 _activeEvents.Add(ev);
-                if (source != null)
-                {
-                    _sourceMappings.Remove(source);
-                    _sourceMappings.Add(source, ev);
-                }
+                
+                if (!source) return;
+                _sourceMappings.Remove(source);
+                _sourceMappings.Add(source, ev);
             }
         }
 
@@ -216,6 +226,38 @@ namespace ADOFAIRenderer.Util.Audio
                 _bgmSamples = null;
                 _bgmDuration = 0;
                 _clipCache.Clear();
+                _isPrimed = false;
+                foreach (var filter in _filters)
+                {
+                    filter.Reset();
+                }
+            }
+        }
+
+        private void PrimeFilters(double totalLatency, double dspTimeBase)
+        {
+            int latencySamples = (int)Math.Round(totalLatency * _targetSampleRate);
+            if (latencySamples <= 0) return;
+
+            // Rent temporary buffer to prime filters with initial audio
+            float[] tempBuffer = System.Buffers.ArrayPool<float>.Shared.Rent(latencySamples * _targetChannels);
+            try
+            {
+                Array.Clear(tempBuffer, 0, latencySamples * _targetChannels);
+
+                // Mix starting from -totalLatency to 0
+                MixBGM(tempBuffer, latencySamples, -totalLatency, dspTimeBase, totalLatency);
+                MixEffectSounds(tempBuffer, latencySamples, -totalLatency, totalLatency);
+
+                // Feed the buffer into filters to prime circular delay buffers
+                foreach (var filter in _filters)
+                {
+                    filter.ProcessBlock(tempBuffer.AsSpan(0, latencySamples * _targetChannels));
+                }
+            }
+            finally
+            {
+                System.Buffers.ArrayPool<float>.Shared.Return(tempBuffer);
             }
         }
 
@@ -226,11 +268,24 @@ namespace ADOFAIRenderer.Util.Audio
 
             lock (_lock)
             {
+                double totalLatency = 0;
+                foreach (var filter in _filters)
+                {
+                    totalLatency += filter.Latency;
+                }
+
+                // Prime filters on first frame execution if latency exists
+                if (!_isPrimed && totalLatency > 0)
+                {
+                    PrimeFilters(totalLatency, dspTimeBase);
+                    _isPrimed = true;
+                }
+
                 // 1. Mix BGM
-                MixBGM(mixedBuffer, samplesNeeded, frameStartTime, dspTimeBase);
+                MixBGM(mixedBuffer, samplesNeeded, frameStartTime, dspTimeBase, totalLatency);
 
                 // 2. Mix Hitsounds/Effect Sounds
-                MixEffectSounds(mixedBuffer, samplesNeeded, frameStartTime);
+                MixEffectSounds(mixedBuffer, samplesNeeded, frameStartTime, totalLatency);
 
                 foreach (var filter in _filters)
                     filter.ProcessBlock(mixedBuffer.AsSpan(0, samplesNeeded * _targetChannels));
@@ -242,7 +297,7 @@ namespace ADOFAIRenderer.Util.Audio
             }
         }
 
-        private void MixBGM(float[] mixedBuffer, int samplesNeeded, double frameStartTime, double dspTimeBase)
+        private void MixBGM(float[] mixedBuffer, int samplesNeeded, double frameStartTime, double dspTimeBase, double totalLatency)
         {
             if (_bgmSamples == null || _bgmSamples.Length == 0) return;
 
@@ -258,13 +313,14 @@ namespace ADOFAIRenderer.Util.Audio
             // BGM Playback start time relative to dspTimeBase
             var time1 = dspTimeSong + separateCountdownOffset;
             var relativeTime1 = time1 - dspTimeBase;
+            var adjustedRelativeTime1 = relativeTime1 - totalLatency;
 
             var totalSamples = _bgmSamples.Length / _targetChannels;
 
             for (int s = 0; s < samplesNeeded; s++)
             {
                 double sampleTime = frameStartTime + (double)s / _targetSampleRate;
-                double clipTime = (sampleTime - relativeTime1) * pitch;
+                double clipTime = (sampleTime - adjustedRelativeTime1) * pitch;
 
                 if (clipTime >= 0 && clipTime < _bgmDuration)
                 {
@@ -287,7 +343,7 @@ namespace ADOFAIRenderer.Util.Audio
             }
         }
 
-        private void MixEffectSounds(float[] mixedBuffer, int samplesNeeded, double frameStartTime)
+        private void MixEffectSounds(float[] mixedBuffer, int samplesNeeded, double frameStartTime, double totalLatency)
         {
             for (var i = _activeEvents.Count - 1; i >= 0; i--)
             {
@@ -301,19 +357,21 @@ namespace ADOFAIRenderer.Util.Audio
 
                 var isSoundFinished = false;
                 var totalSamples = clipData.Samples.Length / _targetChannels;
+                double adjustedStartTime = ev.StartTime - totalLatency;
+                double adjustedEndTime = ev.EndTime >= 0 ? ev.EndTime - totalLatency : -1.0;
 
                 for (var s = 0; s < samplesNeeded; s++)
                 {
                     var sampleTime = frameStartTime + (double)s / _targetSampleRate;
 
                     // If it is a looping sound and has reached or exceeded its end time, stop playing.
-                    if (ev.EndTime >= 0 && sampleTime >= ev.EndTime)
+                    if (adjustedEndTime >= 0 && sampleTime >= adjustedEndTime)
                     {
                         isSoundFinished = true;
                         break;
                     }
 
-                    var elapsed = sampleTime - ev.StartTime;
+                    var elapsed = sampleTime - adjustedStartTime;
                     if (elapsed < 0) continue; // Sound hasn't started yet
 
                     var soundTime = elapsed * ev.Pitch;