PURPOSE: To obtain superior timbre which is not heard so far by supplying a musical sound signal to a processing means selected among plural signal processing means (filter) having mutually different transfer functions (frequency characteristic) according to the characteristics of the musical sound signal.

CONSTITUTION: According to the level of the musical sound signal supplied to an input terminal 20, changeover switches 18 and 22 are switched with a digital code generated by a level decision part 26. For example, when the musical sound signal is supplied to a filter 10, the musical sound signal is processed corresponding to the frequency characteristics of the filter 10 and supplied to an output terminal 24. Namely, when the musical sound signal varies in level, the changeover switches 18 and 22 are switched. When the musical sound signal is supplied to a filter 14, the musical sound signal is processed corresponding to its frequency characteristics and outputted to the output terminal 24. Thus, the waveform of the musical sound signal is processed corresponding to the level of the musical sound signal.