eqfil
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## eqfil

eqfil — Equalizer filter

## Description

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=1. 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.

## Syntax

    asig eqfil ain, kcf, kbw, kgain[, istor]

## Initialization

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.

## Performance

asig -- filtered output signal.

ain -- input signal.

kcf -- filter centre frequency

kbw -- peak/notch bandwidth (Hz).

kgain -- peak/notch gain.

## Examples

Example 137. Example

    kfe         expseg 10, p3*0.9, 180, p3*0.1, 175
    kenv        linen  1000, 0.05, p3, 0.05
    asig        buzz   kenv, kfe, sr/(2*kfe), 1
    afil        eqfil  asig, 1500, 400,  0.1

                out afil

## Credits

Author: Victor Lazzarini;
April 2007

New in version 5.06

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