UTILSLIB::IirFilter Class Reference

Butterworth IIR filter design and application using second-order sections. More...

#include <iirfilter.h>

Public Types
enum	FilterType { LowPass = 0 , HighPass = 1 , BandPass = 2 , BandStop = 3 }
	Filter type selector. More...

Static Public Member Functions
static QVector< IirBiquad >	designButterworth (int iOrder, FilterType type, double dCutoffLow, double dCutoffHigh, double dSFreq)
static Eigen::RowVectorXd	applySos (const Eigen::RowVectorXd &vecData, const QVector< IirBiquad > &sos)
static Eigen::RowVectorXd	applyZeroPhase (const Eigen::RowVectorXd &vecData, const QVector< IirBiquad > &sos)
static Eigen::MatrixXd	applyZeroPhaseMatrix (const Eigen::MatrixXd &matData, const QVector< IirBiquad > &sos)

Detailed Description

Butterworth IIR filter design and application using second-order sections.

All filter types (LP, HP, BP, BS) are supported via the classical analogue-prototype → bilinear-transform design route with pre-warped cutoff frequencies. The resulting biquad cascade is numerically stable for high filter orders.

Typical usage:

// Design a 4th-order zero-phase Butterworth bandpass 1–40 Hz at 1000 Hz sampling rate
auto sos = IirFilter::designButterworth(4, IirFilter::BandPass, 1.0, 40.0, 1000.0);
 
// Apply to one channel
Eigen::RowVectorXd filtered = IirFilter::applyZeroPhase(rawChannel, sos);
 
// Apply to all channels of a matrix
Eigen::MatrixXd matFiltered = IirFilter::applyZeroPhaseMatrix(rawMatrix, sos);

Definition at line 106 of file iirfilter.h.

Member Enumeration Documentation

FilterType

enum UTILSLIB::IirFilter::FilterType

Filter type selector.

Enumerator
LowPass	Low-pass: attenuate above cutoffLow.
HighPass	High-pass: attenuate below cutoffLow.
BandPass	Band-pass: pass cutoffLow–cutoffHigh.
BandStop	Band-stop (notch): attenuate cutoffLow–cutoffHigh.

Definition at line 113 of file iirfilter.h.

Member Function Documentation

applySos()

RowVectorXd IirFilter::applySos ( const Eigen::RowVectorXd & vecData, const QVector< IirBiquad > & sos )

static

Apply a biquad cascade to one data row (causal, single-pass).

Parameters

[in]	vecData	Input row vector.
[in]	sos	Second-order sections from designButterworth().

Returns

Filtered row vector (same length as vecData).

Definition at line 384 of file iirfilter.cpp.

applyZeroPhase()

RowVectorXd IirFilter::applyZeroPhase ( const Eigen::RowVectorXd & vecData, const QVector< IirBiquad > & sos )

static

Apply a biquad cascade with zero-phase (forward + backward pass) to one row. The effective order is doubled and there is no phase distortion.

Parameters

[in]	vecData	Input row vector.
[in]	sos	Second-order sections from designButterworth().

Returns

Zero-phase filtered row vector (same length as vecData).

Definition at line 415 of file iirfilter.cpp.

applyZeroPhaseMatrix()

MatrixXd IirFilter::applyZeroPhaseMatrix ( const Eigen::MatrixXd & matData, const QVector< IirBiquad > & sos )

static

Apply zero-phase filtering to every row of a matrix (each row = one channel).

Parameters

[in]	matData	Input matrix (n_channels x n_samples).
[in]	sos	Second-order sections from designButterworth().

Returns

Filtered matrix (n_channels x n_samples).

Definition at line 436 of file iirfilter.cpp.

designButterworth()

QVector< IirBiquad > IirFilter::designButterworth ( int iOrder, FilterType type, double dCutoffLow, double dCutoffHigh, double dSFreq )

static

Design a Butterworth filter as a cascade of second-order sections.

Parameters

[in]	iOrder	Filter order (≥ 1). For BP/BS the effective order is 2*iOrder.
[in]	type	Filter type: LowPass, HighPass, BandPass, or BandStop.
[in]	dCutoffLow	Lower cutoff frequency in Hz. Used for LP, HP, BP, BS.
[in]	dCutoffHigh	Upper cutoff frequency in Hz. Used for BP and BS only.
[in]	dSFreq	Sampling frequency in Hz.

Returns

QVector of IirBiquad sections (multiply their transfer functions to get H(z)).

Definition at line 175 of file iirfilter.cpp.

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

• src/libraries/dsp/iirfilter.h
• src/libraries/dsp/iirfilter.cpp