RTF_CREATE_CHEBYCHEV(3)

💖 RTF_CREATE_CHEBYCHEV 💖

okay bestie, welcome to the rtfilter library era — this is the RTF_CREATE_CHEBYCHEV(3) page and it's literally all about making IIR filters. yes, both the Chebychev one AND the Butterworth one, they're sharing a page, they're roommates, it's fine 🫶

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✨ NAME ✨

rtf_create_chebychev, rtf_create_butterworth — Creates IIR Chebychev and Butterwoth filters

(that's their typo not mine, we love them anyway 💅)

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🌸 SYNOPSIS 🌸

#include <rtf_common.h>

hfilter rtf_create_chebychev(unsigned int nchann, int proctype,
                             double fc, unsigned int num_pole,
                             int highpass, double r);
hfilter rtf_create_butterworth(unsigned int nchann, int proctype,
                               double fc, unsigned int num_pole,
                               int highpass);

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🦋 DESCRIPTION 🦋

So rtf_create_chebychev() creates an IIR chebychev filter, right? And it's processing nchann channels of data, of the data type that proctype says. You hand it fc as the normalized cutoff frequency, and the filter's Z-transform has num_pole poles — yes, poles, plural, that's the whole vibe — and its impulse response has a ripple of r.

Now that r? It's expressed as the ratio between the overshoot and the unit length. And the overshoot is the difference between the max value of the response to a unit step and the unit length. Important: that ratio is not expressed in decibels, okay? not decibels. periodt.

rtf_create_butterworth() is the exact same thing as rtf_create_chebychev() except it creates a butterworth filter — which is a special case of a chebychev filter with a ripple of 0. iconic, honestly. so much range 🎀

A normalized frequency is the ratio between the absolute frequency and the sampling frequency. So like, a value of 1.0 refers to the sampling frequency. iykyk.

And the highpass thing:

• if highpass is 0, it specifies the filter should be a lowpass
• if highpass is non-zero, the should be a highpass

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⭐ RETURN VALUE ⭐

Returns the handle to the created filter in case of success, NULL otherwise.

so like... check it, bestie. don't just assume. 🙈

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💜 SEE ALSO 💜

• rtf_create_filter(3)
• rtf_destroy_filter(3)

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ok that's the whole page, no cap. go make some filters, main character 💅✨

later babes — this was the rtfilter library, EPFL, 2010 🎀💖