IirBiquad

Namespace: RTPROCESSINGLIB  ·  Library: DSP Library

#include <dsp/iirfilter.h>

struct UTILSLIB::IirBiquad

Coefficients of one second-order IIR section (biquad).

Transfer function (Direct-Form II):

H(z) = (b0 + b1*z^-1 + b2*z^-2) / (1 + a1*z^-1 + a2*z^-2)

Note: a0 is normalised to 1. For first-order sections set b2 = a2 = 0.

src/examples/ex_dsp_spectral/main.cpp

const QVector<IirBiquad> sos = IirFilter::designButterworth(4, IirFilter::LowPass, 30.0, 0.0, kSFreq);
const RowVectorXd lowPassed = IirFilter::applyZeroPhase(signal, sos); // forward-backward, no phase shift

---

Example

• Full source: src/examples/ex_dsp_spectral/main.cpp
• Build target: ex_dsp_spectral (runs under CTest)

Used in examples

ex_dsp_spectral

Spectral and filtering tools of the dsp library on signals with known content.

src/examples/ex_dsp_spectral/main.cpp, line 97

double gainAt(const QVector<IirBiquad>& sos, double freq)
{
    const std::complex<double> z = std::polar(1.0, -2.0 * kPi * freq / kSFreq); // z^-1
    std::complex<double> h(1.0, 0.0);
    for (const IirBiquad& s : sos) {
        h *= (s.b0 + s.b1 * z + s.b2 * z * z) / (1.0 + s.a1 * z + s.a2 * z * z);
    }
    return std::abs(h);
}

Authors of this file

• Christoph Dinh <christoph.dinh@mne-cpp.org>