PURPOSE: To understand an accurate level of a compound signal by selecting properly whether the signal supplied to a level meter is limited only to a channel input of a compound signal added with a signal of another channel by means of a track/channel changeover switch.

CONSTITUTION: An input changeover switch 6 has a pair of contacts which are connected to a pair of mixer circuits 13 and 14 respectively in addition to a contact connected to a corresponding input amplifier circuit 21 or 24. A switch 15 or 16 is closed to add together input signals of an optional channel, and this added signal can be supplied equally to an input selection switch 6 of each channel. While level meters 41W44 of each channel are connected between an input signal line 5 and an output signal line 9 via a changeover switch 17. These level meters are switched to a contact 17t of the track side to display the signal level of a track and to a contact 17c of the channel side to display the signal level of a channel respectively.