Added more sound effeects. Added audio manager.

AlientAttack.MonoGame/Audio/SoundPool.cs

@@ -0,0 +1,37 @@
+using Microsoft.Xna.Framework.Audio;
+using System;
+
+namespace AlienAttack.MonoGame.Audio;
+
+public sealed class SoundPool
+{
+    private readonly SoundEffectInstance[] _voices;
+    private int _cursor;
+
+    public SoundPool(SoundEffect effect, int maxVoices)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(maxVoices, 1);
+
+        _voices = new SoundEffectInstance[maxVoices];
+
+        for (int i = 0; i < maxVoices; i++)
+            _voices[i] = effect.CreateInstance();
+    }
+
+    public void Play(float volume = 1f, float pitch = 0f, float pan = 0f)
+    {
+        SoundEffectInstance instance = _voices[_cursor];
+
+        _cursor = (_cursor + 1) % _voices.Length;
+
+        // "Voice stealing": stop if currently playing, then reuse immediately
+        if (instance.State == SoundState.Playing)
+            instance.Stop();
+
+        instance.Volume = Math.Clamp(volume, 0f, 1f);
+        instance.Pitch = Math.Clamp(pitch, -1f, 1f);
+        instance.Pan = Math.Clamp(pan, -1f, 1f);
+
+        instance.Play();
+    }
+}