Unrevert audio (#21330)

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>

Content.Shared/CCVar/CCVars.cs

@@ -69,6 +69,8 @@ namespace Content.Shared.CCVar
         public static readonly CVarDef<float> AmbienceVolume =
             CVarDef.Create("ambience.volume", 0.0f, CVar.ARCHIVE | CVar.CLIENTONLY);
 
+        public const float MasterMultiplier = 2f;
+
         // Midi is on engine so deal
         public const float MidiMultiplier = 3f;