Functions > Signal Processing > Digital Filtering > IIR Filter Coefficients
IIR Filter Coefficients
bessel(n, scale)—Returns coefficients for an analog Bessel filter of order n; scale controls the gain at cutoff. The output is used as an argument to one of the IIR filter functions.
butter(n)—Returns coefficients for an analog Butterworth filter of order n. The output is used as an argument to one of the IIR filter functions.
cheby1(n, e)—Returns coefficients for a Type I Chebyshev analog filter of order n; ripple is controlled by the parameter e. The output is used as an argument to one of the IIR filter functions.
cheby2(n, scale, atten)—Returns coefficients for a Type II Chebyshev analog filter of order n with the lower edge of the stopband at scale and stopband attenuation atten. The output is an argument to the IIR filter functions.
Arguments
n is an integer filter order:
For bessel filters, n is between 1 and 35
For all others, n is between 1 and 200.
e is a positive real number representing the allowable passband ripple.
scale is a calculated real number greater than 1 setting the lower edge of the stopband:
For bessel filters, it is a real number greater than 0 which can be used to control the gain at the cuttoff frequency.
For cheby2 filters, it is a calculated real number greater than 1 setting the lower edge of the stopband.
atten is a real number greater than 1, the stopband attenuation factor.
Additional Information
These functions produce coefficient arrays with an even number of columns:
If there are two columns, as in the output of bessel, the filter consists of a single section: column 1 contains coefficients of the transfer function numerator, column 2 contains denominator coefficients.
If there are more than two columns, each pair represents a section of a filter in cascade form.
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