amadeus: Add missing compressor effect from REV11 (#4010)

* amadeus: Add missing compressor effect from REV11

This was in my reversing notes but seems I completely forgot to
implement it

Also took the opportunity to simplify the Limiter effect a bit.

* Remove some outdated comment

* Address gdkchan's comments

Ryujinx.Audio/Renderer/Dsp/FloatingPointHelper.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Reflection.Metadata;
 using System.Runtime.CompilerServices;
 
 namespace Ryujinx.Audio.Renderer.Dsp
@@ -46,6 +47,53 @@ namespace Ryujinx.Audio.Renderer.Dsp
             return MathF.Pow(10, x);
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static float Log10(float x)
+        {
+            // NOTE: Nintendo uses an approximation of log10, we don't.
+            // As such, we support the same ranges as Nintendo to avoid unexpected behaviours.
+            return MathF.Pow(10, MathF.Max(x, 1.0e-10f));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static float MeanSquare(ReadOnlySpan<float> inputs)
+        {
+            float res = 0.0f;
+
+            foreach (float input in inputs)
+            {
+                res += (input * input);
+            }
+
+            res /= inputs.Length;
+
+            return res;
+        }
+
+        /// <summary>
+        /// Map decibel to linear.
+        /// </summary>
+        /// <param name="db">The decibel value to convert</param>
+        /// <returns>Converted linear value/returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static float DecibelToLinear(float db)
+        {
+            return MathF.Pow(10.0f, db / 20.0f);
+        }
+
+        /// <summary>
+        /// Map decibel to linear in [0, 2] range.
+        /// </summary>
+        /// <param name="db">The decibel value to convert</param>
+        /// <returns>Converted linear value in [0, 2] range</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static float DecibelToLinearExtended(float db)
+        {
+            float tmp = MathF.Log2(DecibelToLinear(db));
+
+            return MathF.Truncate(tmp) + MathF.Pow(2.0f, tmp - MathF.Truncate(tmp));
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static float DegreesToRadians(float degrees)
         {