Regarding what to type into the parameter of this given function

Hi,
1st of all I think the method you mentioned may be in VB.NET. Because VB.NET it's "Public", in C# it's "public" though. Any way syntax not a matter here. Below explaining your function parameter. Your function contains a parameter of type Constants.SilentLoud

This type Constants.SilentLoud might have been defined in your application. I hope it's an enumerator. But I can't assume it without seeing it's definition.
More over your parameter is optional. That's saying here([Optional, i.e. you can assign parameter value if you need. You can also ignore this parameter if you don't need.
If you ignore 1st parameter, a default value will be assigned automatically. That's saying inside DefaultValue(Constants.SilentLoud.Loud)]

Hope this helps...