actually resample stella's audio

src/BizHawk.Emulation.Cores/Consoles/Atari/Stella/Stella.IEmulator.cs

@@ -58,6 +58,7 @@ namespace BizHawk.Emulation.Cores.Atari.Stella
 		public void Dispose()
 		{
 			_elf.Dispose();
+			DisposeSound();
 		}
 	}
 }

src/BizHawk.Emulation.Cores/Consoles/Atari/Stella/Stella.ISoundProvider.cs

@@ -1,12 +1,13 @@
-using System.Runtime.InteropServices;
-
-using BizHawk.Emulation.Common;
+using BizHawk.Emulation.Common;
 using BizHawk.Common;
 
 namespace BizHawk.Emulation.Cores.Atari.Stella
 {
 	public partial class Stella : ISoundProvider
 	{
+		private BlipBuffer _blipL, _blipR;
+		private int _latchL, _latchR;
+
 		private readonly short[] _samples = new short[4096];
 		private int _nsamp;
 
@@ -20,9 +21,7 @@ namespace BizHawk.Emulation.Cores.Atari.Stella
 		}
 
 		public void DiscardSamples()
-		{
-			_nsamp = 0;
-		}
+			=> _nsamp = 0;
 
 		public void SetSyncMode(SyncSoundMode mode)
 		{
@@ -30,26 +29,89 @@ namespace BizHawk.Emulation.Cores.Atari.Stella
 			{
 				throw new NotSupportedException("Async mode is not supported.");
 			}
-
 		}
+
 		public SyncSoundMode SyncMode => SyncSoundMode.Sync;
 
 		public void GetSamplesAsync(short[] samples)
-		{
-			throw new InvalidOperationException("Async mode is not supported.");
-		}
+			=> throw new InvalidOperationException("Async mode is not supported.");
 
-		private void UpdateAudio()
+		private unsafe void UpdateAudio()
 		{
 			var src = IntPtr.Zero;
-			Core.stella_get_audio(ref _nsamp, ref src);
+			var nsamp = 0;
+			Core.stella_get_audio(ref nsamp, ref src);
 
 			if (src != IntPtr.Zero)
 			{
 				using (_elf.EnterExit())
 				{
-					Marshal.Copy(src, _samples, 0, _nsamp * 2);
+					var samplePtr = (ushort*)src.ToPointer();
+					for (uint i = 0; i < nsamp; i++)
+					{
+						int sample = *samplePtr++;
+						if (sample != _latchL)
+						{
+							var diff = _latchL - sample;
+							_latchL = sample;
+							_blipL.AddDelta(i, diff);
+						}
+
+						sample = *samplePtr++;
+						if (sample != _latchR)
+						{
+							var diff = _latchR - sample;
+							_latchR = sample;
+							_blipR.AddDelta(i, diff);
+						}
+					}
 				}
+
+				_blipL.EndFrame((uint)nsamp);
+				_blipR.EndFrame((uint)nsamp);
+
+				_nsamp = _blipL.SamplesAvailable();
+				if (_nsamp != _blipR.SamplesAvailable())
+				{
+					throw new InvalidOperationException("Audio processing error");
+				}
+
+				_blipL.ReadSamplesLeft(_samples, _nsamp);
+				_blipR.ReadSamplesRight(_samples, _nsamp);
+			}
+			else
+			{
+				_nsamp = 0;
+			}
+		}
+
+		private void InitSound(int fps)
+		{
+			var sampleRate = fps switch
+			{
+				60 => 262 * 76 * 60 / 38, // 31440Hz
+				50 => 312 * 76 * 50 / 38, // 31200Hz
+				_ => throw new InvalidOperationException()
+			};
+
+			_blipL = new(2048);
+			_blipL.SetRates(sampleRate, 44100);
+			_blipR = new(2048);
+			_blipR.SetRates(sampleRate, 44100);
+		}
+
+		private void DisposeSound()
+		{
+			if (_blipL != null)
+			{
+				_blipL.Dispose();
+				_blipL = null;
+			}
+
+			if (_blipR != null)
+			{
+				_blipR.Dispose();
+				_blipR = null;
 			}
 		}
 	}

src/BizHawk.Emulation.Cores/Consoles/Atari/Stella/Stella.cs

@@ -62,6 +62,8 @@ namespace BizHawk.Emulation.Cores.Atari.Stella
 
 					Core.stella_get_frame_rate(out var fps);
 
+					InitSound(fps);
+
 					var regionId = Core.stella_get_region();
 					Region = regionId switch
 					{
@@ -85,7 +87,6 @@ namespace BizHawk.Emulation.Cores.Atari.Stella
 
 					Core.stella_set_input_callback(_inputCallback);
 
-					// Getting cartridge type
 					var ptr = Core.stella_get_cart_type();
 					var cartType = Marshal.PtrToStringAnsi(ptr);
 					Console.WriteLine($"[Stella] Cart type loaded: {cartType}");