Method and apparatus for dynamic midi synthesizer filter control

TLDR: In this article, a method and apparatus for the dynamic control of a MIDI synthesizer filter is described, where 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.

Abstract: A method and apparatus are disclosed for the dynamic control of a MIDI synthesizer filter. 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 utilized to calculate appropriate filter coefficients so that the center 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 utilized 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.