Abstract: An acoustic signal processing apparatus comprising infinite impulse response type digital filters and phase control device. The filters receive an acoustic signal. Outputs from the filters are synthesized to generate an output signal. The phase control device controls the phase of the output signals so as to cause limit cycle noise components generated by the filters to cancel each other on synthesizing.

Abstract: Two tone generators having different tone generation systems, e.g., PCM type and FM type, are provided. There are tone generation modes designating combination of tone generation in these tone generators and one can be selected from among them. There are, for example, a simple mixing mode, a delay mode in which start of tone generation in one tone generator is delayed from that in the other and a crossfade mode in which a tone signal is generated first in one tone generator and tone generation is switched to the other tone generator and envelope levels of output tone signals of the two tone generators are crossfaded during a switching period. Delay time in the delay mode and switching time in the crossfade mode can be variably controlled in accordance with a key scaling and/or other factors. A tone may be generated at a sampling frequency synchronized with a pitch in one tone generator and at a sampling frequency which is not synchronized with the pitch in the other tone generator.