Ground Layer Shield

The PCBs of the karacter have a total of none less than six layers: While the first five are used for separately routing audio and power supply, the sixth one is a dedicated ground shield layer. But what's the idea behind this?

As the additional ground layer is placed extremely close beneath the traces which carry audio, it is very efficient as a shield against unwanted noise interferences caused by electric fields. The result is even less noise – at least the one you don't want to have ;-)