Digital filter for a music synthesizer

摘要

A digital filter controlled by a plurality of filter coefficients is preferably coupled to the output of an excitation signal source within a MIDI synthesizer. The excitation signal source is typically controlled by a MIDI data file comprising a sequential series of program control commands and matching note on and note off commands. A plurality of filter coefficient factors are stored in memory and periodically accessed in response to variations in the program control commands and matching note on and note off commands. The selected filter coefficient factors are then utilised to calculate appropriate filter coefficients so that the centre frequency and filter Q of the digital filter may be dynamically and optimally controlled. In a preferred embodiment of the present invention a filter control circuit is also utilised to limit the output of the filter to a maximum level so that output stability is always maintained, independent of the initial conditions and filter coefficients of the filter.