Assembly: Microsoft.Xna.Framework (in microsoft.xna.framework.dll)
The sound effect master volume affects all sound effect instances, including currently playing instances and newly created instances. Each SoundEffectInstance also has its own volume (SoundEffectInstance.Volume) that is relative to the master volume.
You can adjust the volume of all sounds effects by changing MasterVolume. You can adjust the volume of an individual SoundEffectInstance by changing SoundEffectInstance.Volume, or by specifying an instance volume when you call Play to create the instance.