PURPOSE: To obtain a sound field with full ambience, by controlling the level of an indirect sound and at the same time generating an indirect sound for each frequency band.

CONSTITUTION: Control signals (L-R/L+R) are obtained from the sum and difference of both left/right channel input signals L and R. At the same time, an indirect sound is synthesized from signals L and R. This indirect sound is supplied to an amplifier 7 having its gain to be controlled by the level of the control signal. The signals L and R are divided with each frequency band through BPFs 101, 102... and then processed for each frequency band. Thus it is possible to control the sound field with each band. Furthermore it is possible to increase the sound image of only background orchestra while the vocal kept at the normal position.