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);
         }
     }
 }