dspark::FIRDesign< T > Class Template Reference

Static methods for designing FIR filter coefficients. More...

#include <FIRFilter.h>

Static Public Member Functions
static std::vector< T >	lowPass (double sampleRate, double cutoffHz, int numTaps, T beta=T(5)) noexcept
	Designs a low-pass FIR filter.
static std::vector< T >	highPass (double sampleRate, double cutoffHz, int numTaps, T beta=T(5)) noexcept
	Designs a high-pass FIR filter.
static std::vector< T >	bandPass (double sampleRate, double lowCutoffHz, double highCutoffHz, int numTaps, T beta=T(5)) noexcept
	Designs a band-pass FIR filter.
static std::vector< T >	bandStop (double sampleRate, double lowCutoffHz, double highCutoffHz, int numTaps, T beta=T(5)) noexcept
	Designs a band-stop (notch) FIR filter.
static int	estimateTaps (double sampleRate, double transitionHz, double attenuationDb) noexcept
	Estimates the required number of taps for a given specification.
static T	estimateKaiserBeta (double attenuationDb) noexcept
	Estimates the Kaiser beta parameter for a desired attenuation.

Detailed Description

template<typename T>
class dspark::FIRDesign< T >

Static methods for designing FIR filter coefficients.

Uses the windowed-sinc method: an ideal (sinc) impulse response is multiplied by a window function to produce a realisable FIR filter.

All methods return a vector of filter coefficients (taps). The number of taps determines the filter's steepness and stopband attenuation. More taps = steeper transition but more latency and computation.

Rule of thumb for number of taps:

• N ~ 4 / (transitionWidth / sampleRate) for a Kaiser window
• For a 1 kHz transition band at 48 kHz: N ~ 4 / (1000/48000) ~ 192 taps
• Always use an odd number for symmetric (Type I) FIR filters

Template Parameters

T	Coefficient type (float or double).

Definition at line 74 of file FIRFilter.h.

Member Function Documentation

bandPass()

template<typename T >

static std::vector< T > dspark::FIRDesign< T >::bandPass ( double  sampleRate, double  lowCutoffHz, double  highCutoffHz, int  numTaps, T  beta = T(5)  )

inlinestaticnoexcept

Designs a band-pass FIR filter.

Created by subtracting a low-pass at lowCutoff from a low-pass at highCutoff.

Parameters

sampleRate	Sample rate in Hz.
lowCutoffHz	Lower cutoff frequency in Hz.
highCutoffHz	Upper cutoff frequency in Hz.
numTaps	Number of filter taps (must be odd, >= 3).
beta	Kaiser window beta.

Returns

Vector of filter coefficients.

Definition at line 125 of file FIRFilter.h.

bandStop()

template<typename T >

static std::vector< T > dspark::FIRDesign< T >::bandStop ( double  sampleRate, double  lowCutoffHz, double  highCutoffHz, int  numTaps, T  beta = T(5)  )

inlinestaticnoexcept

Designs a band-stop (notch) FIR filter.

Parameters

sampleRate	Sample rate in Hz.
lowCutoffHz	Lower cutoff frequency in Hz.
highCutoffHz	Upper cutoff frequency in Hz.
numTaps	Number of filter taps (must be odd, >= 3).
beta	Kaiser window beta.

Returns

Vector of filter coefficients.

Definition at line 152 of file FIRFilter.h.

estimateKaiserBeta()

template<typename T >

static T dspark::FIRDesign< T >::estimateKaiserBeta ( double  attenuationDb )

inlinestaticnoexcept

Estimates the Kaiser beta parameter for a desired attenuation.

Parameters

attenuationDb

Desired stopband attenuation in dB (positive).

Returns

Kaiser beta parameter.

Definition at line 204 of file FIRFilter.h.

estimateTaps()

template<typename T >

static int dspark::FIRDesign< T >::estimateTaps ( double  sampleRate, double  transitionHz, double  attenuationDb  )

inlinestaticnoexcept

Estimates the required number of taps for a given specification.

Uses the Kaiser formula to estimate the minimum number of odd taps needed to achieve the desired stopband attenuation with a given transition bandwidth.

Parameters

sampleRate	Sample rate in Hz.
transitionHz	Width of the transition band in Hz. Must be > 0.
attenuationDb	Desired stopband attenuation in dB (positive value, e.g., 60).

Returns

Estimated number of taps (always odd).

Definition at line 185 of file FIRFilter.h.

highPass()

template<typename T >

static std::vector< T > dspark::FIRDesign< T >::highPass ( double  sampleRate, double  cutoffHz, int  numTaps, T  beta = T(5)  )

inlinestaticnoexcept

Designs a high-pass FIR filter.

Created by spectrally inverting a low-pass filter.

Parameters

sampleRate	Sample rate in Hz.
cutoffHz	Cutoff frequency in Hz.
numTaps	Number of filter taps (must be odd, >= 3).
beta	Kaiser window beta.

Returns

Vector of filter coefficients.

Definition at line 105 of file FIRFilter.h.

lowPass()

template<typename T >

static std::vector< T > dspark::FIRDesign< T >::lowPass ( double  sampleRate, double  cutoffHz, int  numTaps, T  beta = T(5)  )

inlinestaticnoexcept

Designs a low-pass FIR filter.

Parameters

sampleRate	Sample rate in Hz.
cutoffHz	Cutoff frequency in Hz (-6 dB point).
numTaps	Number of filter taps (must be odd, >= 3).
beta	Kaiser window beta (default: 5.0). Higher = more attenuation.

Returns

Vector of filter coefficients.

Definition at line 86 of file FIRFilter.h.

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The documentation for this class was generated from the following file:

• Core/FIRFilter.h