What is fringing effect?

Apparent boost in lows because of full track being played on multitrack machines.

If you have two parallel plates forming a capacitor, the electric field does not end abruptly at the edge of the plates. There is some field outside that plates that curves from one to the other. This causes the real capacitance to be larger than what you'd calculate using the ideal formula. You have more electric field because of the fringe fields.