While a normal tone of a designated pitch is being generated in response to key depression or other performance operation on a keyboard or other performance operation device, the tone is controlled in response to manipulation of a pedal or other auxiliary performance operator. Thus, dubbing of editing material and dubbing of the final video program can be performed efficiently. As a result, in the COC type semiconductor device, when interconnecting a plurality of semiconductor chips, their electrode terminals can be joined to each other without deteriorating the properties of these chips owing to the high temperature applied thereon. An electric characteristic of the TFT is thus improved. The DC-DC converter of some variations performs pulse frequency modulation control at light loads, and includes a reducing circuit configured to skip an oscillation frequency signal at light loads and to generate a skipped signal.