LowPassFilterRC Class Reference

#include <filterrc.h>

Public Member Functions
	LowPassFilterRC (Real timeconst)
void	configure (Real timeout)
void	process (const Real &sample_in, Real &sample_out)

Private Attributes
Real	m_timeconst
Real	m_y1
Real	m_a1
Real	m_b0

Detailed Description

First order low-pass IIR filter for real-valued signals.

Definition at line 26 of file filterrc.h.

Constructor & Destructor Documentation

LowPassFilterRC()

LowPassFilterRC::LowPassFilterRC

(

Real

timeconst

)

Construct 1st order low-pass IIR filter.

timeconst :: RC time constant in seconds (1 / (2 * PI * cutoff_freq)

Definition at line 23 of file filterrc.cpp.

References exp(), m_a1, m_b0, and m_timeconst.

                                               :
    m_timeconst(timeconst),
    m_y1(0)
{
    m_a1 = - exp(-1/m_timeconst);
    m_b0 = 1 + m_a1;
}

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Member Function Documentation

configure()

void LowPassFilterRC::configure

(

Real

timeout

)

Reconfigure filter with new time constant

Definition at line 32 of file filterrc.cpp.

References exp(), m_a1, m_b0, m_timeconst, and m_y1.

Referenced by BFMDemod::applyAudioSampleRate(), and BFMDemod::BFMDemod().

{
    m_timeconst = timeconst;
    m_y1 = 0;
    m_a1 = - exp(-1/m_timeconst);
    m_b0 = 1 + m_a1;

    qDebug() << "LowPassFilterRC::configure: t: " << m_timeconst
            << " a1: " << m_a1
            << " b0: " << m_b0;
}

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process()

void LowPassFilterRC::process	(	const Real &	sample_in,
		Real &	sample_out
	)

Process samples.

Definition at line 45 of file filterrc.cpp.

References m_a1, m_b0, and m_y1.

Referenced by BFMDemod::feed().

{
    /*
     * Continuous domain:
     *   H(s) = 1 / (1 - s * timeconst)
     *
     * Discrete domain:
     *   H(z) = (1 - exp(-1/timeconst)) / (1 - exp(-1/timeconst) / z)
     */

    m_y1 = (sample_in * m_b0) - (m_y1 * m_a1);
    sample_out = m_y1;
}

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Member Data Documentation

m_a1

Real LowPassFilterRC::m_a1

private

Definition at line 48 of file filterrc.h.

Referenced by configure(), LowPassFilterRC(), and process().

m_b0

Real LowPassFilterRC::m_b0

private

Definition at line 49 of file filterrc.h.

Referenced by configure(), LowPassFilterRC(), and process().

m_timeconst

Real LowPassFilterRC::m_timeconst

private

Definition at line 46 of file filterrc.h.

Referenced by configure(), and LowPassFilterRC().

m_y1

Real LowPassFilterRC::m_y1

private

Definition at line 47 of file filterrc.h.

Referenced by configure(), and process().

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

• sdrbase/dsp/filterrc.h
• sdrbase/dsp/filterrc.cpp