Digital waveform data stored in a waveform memory is read out in response to the ON/OFF operations of key switches such as a keyboard of an electronic musical instrument. The waveform data is passed through a low-pass filter, then subjected to amplitude envelope processing such as attack, decay, release, and the like. The processed waveform data is D/A-converted to output it as a tone signal. A look-up table that stores resonant frequency data and resonance sharpness data (quality factor) of a filter in correspondence with the touch (operation strength or key-ON velocity) of the switch operation at, e.g., the keyboard is used. The resonant frequency and resonance sharpness data are read out from the table in correspondence with the touch data of the keyboard operation to control filter characteristics such as a cutoff frequency, roll-off or slope, and the like, by coefficient data to the filter.