when this key is off the slope of the low cut becomes flat display in the display section 25 is extinguished and the operation of the p down key 36 is not accepted any longer when this key is turned on from the off state the previous set values are displayed these are keys used when characteristics of the three divided regions should be established these keys correspond respectively to the low middle and high frequency regions if the low key 40 is depressed and the up down key 36 is operated the level of the low frequency region is established if the low key 40 is depressed and then the frequency key 32 is depressed and the up down key 36 is operated the center frequency fl of the low frequency region is established if the low key 40 is depressed and then the q slope key 34 is depressed and the up down key 6 is operated q of the low frequency region is established similarly with respect to the middle and high frequency regions the respective parameters can be established by depressing the middle key 42 and high key 44 and performing the similar operations this is a key for establishing the high cut characteristics and the high cut frequency and its slope can be established by performing similar operation to the low cut key 38 when this key has been turned off the slope of the high cut becomes flat the operation of the up down key 36 is not accepted any longer and the display in the display section 28 is extinguished a set value before the key 46 is.