If you used before the normal then, it shows that the settings of what no problem, the envelope that can only eliminate the fixed interference, such as within the scope of the installation by the shelf, or what causes inaccurate level detection;
If you use before normal, that means that there is no problem with the setup, envelope that can only eliminate fixed interference, such as within the scope of the installation by the shelf, or what causes inaccurate level detection.
The envelope can only eliminate fixed interference, such as the installation range by the shelf, or whatever caused the level detection inaccuracy;