eqfil — Equalizer filter
The opcode eqfil is a 2nd order tunable equalisation filter based on Regalia and Mitra design ("Tunable Digital Frequency Response Equalization Filters", IEEE Trans. on Ac., Sp. and Sig Proc., 35 (1), 1987). It provides a peak/notch filter for building parametric/graphic equalisers.
The amplitude response for this filter will be flat (=1) for kgain=0. With kgain is bigger than 1, there will be a peak at the centre frequency, whose width is given by the kbw parameter, but outside this band, the response will tend towards 1. Conversely, if kgain is smaller than 1, a notch will be created around the CF.
istor --initial disposition of internal data space. Since filtering incorporates a feedback loop of previous output, the initial status of the storage space used is significant. A zero value will clear the space; a non-zero value will allow previous information to remain. The default value is 0.
asig -- filtered output signal.
ain -- input signal.
kcf -- filter centre frequency
kbw -- peak/notch bandwidth (Hz).
kgain -- peak/notch gain.