StateVariable< FILTER_TYPE > Class Template Reference

State Variable Filter (approximation of Chamberlin version) Informed by pseudocode at http://www.musicdsp.org/showone.php?id=23 and. More...

#include <StateVariable.h>

Detailed Description

template<int8_t FILTER_TYPE>
class StateVariable< FILTER_TYPE >

State Variable Filter (approximation of Chamberlin version) Informed by pseudocode at http://www.musicdsp.org/showone.php?id=23 and.

http://www.musicdsp.org/showone.php?id=142. Here's the original:

cutoff = cutoff freq in Hz fs = sampling frequency //(e.g. 44100Hz) f = 2 sin (pi * cutoff / fs) //[approximately] q = resonance/bandwidth [0 < q <= 1] most res: q=1, less: q=0 low = lowpass output high = highpass output band = bandpass output notch = notch output

scale = q

low=high=band=0;

–beginloop low = low + f * band; high = scale * input - low - q*band; band = f * high + band; notch = high + low;

–endloop

References : Hal Chamberlin, Musical Applications of Microprocessors, 2nd Ed, Hayden Book Company 1985. pp 490-492. Jon Dattorro, Effect Design Part 1, J. Audio Eng. Soc., Vol 45, No. 9, 1997 September A State Variable filter which offers 12db resonant low, high, bandpass and notch modes.

Template Parameters

FILTER_TYPE

choose between LOWPASS, BANDPASS, HIGHPASS and NOTCH.

Note

To save processing time, this version of the filter does not saturate internally, so any resonant peaks are unceremoniously truncated. It may be worth adding code to constrain the internal variables to enable resonant saturating effects.

Definition at line 65 of file StateVariable.h.

Public Member Functions
	StateVariable ()
	Constructor.
void	setResonance (Q0n8 resonance)
	Set how resonant the filter will be. More...
void	setCentreFreq (unsigned int centre_freq)
	Set the centre or corner frequency of the filter. More...
int	next (int input)
	Calculate the next sample, given an input signal. More...

Member Function Documentation

next()

template<int8_t FILTER_TYPE>

int StateVariable< FILTER_TYPE >::next ( int  input )

inline

Calculate the next sample, given an input signal.

Parameters

input

the signal input.

Returns

the signal output.

Note

Timing: 16 - 20 us

Definition at line 112 of file StateVariable.h.

setCentreFreq()

template<int8_t FILTER_TYPE>

void StateVariable< FILTER_TYPE >::setCentreFreq ( unsigned int  centre_freq )

inline

Set the centre or corner frequency of the filter.

Parameters

centre_freq

20 - 4096 Hz (MOZZI_AUDIO_RATE/4). This will be the cut-off frequency for LOWPASS and HIGHPASS, and the centre frequency to pass or reduce for BANDPASS and NOTCH.

Note

Timing 25-30us

The frequency calculation is VERY "approximate". This really needs to be fixed.

Definition at line 94 of file StateVariable.h.

setResonance()

template<int8_t FILTER_TYPE>

void StateVariable< FILTER_TYPE >::setResonance ( Q0n8  resonance )

inline

Set how resonant the filter will be.

Parameters

resonance

a byte value between 1 and 255. The lower this value is, the more resonant the filter. At very low values, the filter can output loud peaks which can exceed Mozzi's output range, so you may need to attenuate the output in your sketch.

Note

Timing < 500 ns

Definition at line 79 of file StateVariable.h.