Added AY38912 support

Core/Audio/Ay38912.cs

@@ -0,0 +1,69 @@
+using System;
+
+namespace Core.Audio
+{
+    public class Ay38912
+    {
+        private readonly byte[] _registers = new byte[16];
+        private byte _selectedRegister = 0;
+
+        // The AY-3-8912 uses logarithmic volume, not linear! 
+        // This table converts the 0-15 register value into a precise float multiplier.
+        private readonly float[] _volumeTable = {
+            0.0000f, 0.0137f, 0.0205f, 0.0291f, 0.0423f, 0.0618f, 0.0847f, 0.1369f,
+            0.1691f, 0.2647f, 0.3527f, 0.4499f, 0.5704f, 0.6873f, 0.8482f, 1.0000f
+        };
+
+        // --- Hardware Port Intercepts ---
+        public void SelectRegister(byte register)
+        {
+            _selectedRegister = (byte)(register & 0x0F); // Only 16 registers exist
+        }
+
+        public void WriteRegister(byte value)
+        {
+            _registers[_selectedRegister] = value;
+        }
+
+        public byte ReadRegister()
+        {
+            return _registers[_selectedRegister];
+        }
+
+        // --- Audio Math Generators ---
+
+        // The AY clock on a Spectrum 128 is 1.7734 MHz. 
+        // The chip divides this by 16 internally, giving a base clock of ~110,837 Hz.
+        private float GetFrequency(int registerLow, int registerHigh)
+        {
+            int period = _registers[registerLow] | ((_registers[registerHigh] & 0x0F) << 8);
+            if (period == 0) return 0f; // Prevent divide-by-zero
+            return 110837.5f / period;
+        }
+
+        private float GetVolume(int volumeRegister)
+        {
+            byte vol = _registers[volumeRegister];
+
+            // Bit 4 indicates if the channel is using the hardware Envelope generator.
+            // For Version 1 of our chip, if the envelope is active, we will just 
+            // output half volume so the game doesn't go silent!
+            if ((vol & 0x10) != 0)
+            {
+                return 0.5f;
+            }
+
+            return _volumeTable[vol & 0x0F];
+        }
+
+        // --- Public Data for your Audio Engine ---
+        public float FreqA => GetFrequency(0, 1);
+        public float FreqB => GetFrequency(2, 3);
+        public float FreqC => GetFrequency(4, 5);
+
+        // Register 7 is the Mixer. Bit 0, 1, and 2 turn the tone channels OFF when set to 1.
+        public float VolA => (_registers[7] & 0x01) == 0 ? GetVolume(8) : 0f;
+        public float VolB => (_registers[7] & 0x02) == 0 ? GetVolume(9) : 0f;
+        public float VolC => (_registers[7] & 0x04) == 0 ? GetVolume(10) : 0f;
+    }
+}