Kwave::LowPassFilter Class Reference

#include <LowPassFilter.h>

Inheritance diagram for Kwave::LowPassFilter:

Collaboration diagram for Kwave::LowPassFilter:

Public Slots
void	input (Kwave::SampleArray data)
void	setFrequency (const QVariant fc)

Signals
void	output (Kwave::SampleArray data)
Signals inherited from Kwave::StreamObject
void	attributeChanged (const QVariant value)

Public Member Functions
	LowPassFilter ()
virtual	~LowPassFilter () Q_DECL_OVERRIDE
virtual double	at (double f) Q_DECL_OVERRIDE
virtual void	goOn () Q_DECL_OVERRIDE
Public Member Functions inherited from Kwave::SampleSource
	SampleSource (QObject *parent=Q_NULLPTR)
virtual	~SampleSource ()
virtual bool	done () const
Public Member Functions inherited from Kwave::StreamObject
	StreamObject (QObject *parent=Q_NULLPTR)
virtual	~StreamObject ()
virtual unsigned int	tracks () const
virtual Kwave::StreamObject *	operator[] (unsigned int track)
virtual unsigned int	tracksOfPort (const char *port) const
virtual Kwave::StreamObject *	port (const char *port, unsigned int track)
virtual unsigned int	blockSize () const
void	setAttribute (const char *attribute, const QVariant &value)
Public Member Functions inherited from Kwave::TransmissionFunction
virtual	~TransmissionFunction ()

Private Member Functions
void	initFilter ()
void	normed_setfilter_shelvelowpass (double freq)

Private Attributes
Kwave::SampleArray	m_buffer
double	m_f_cutoff
struct {
double   cx
double   cx1
double   cx2
double   cy1
double   cy2
double   x
double   x1
double   x2
double   y
double   y1
double   y2
}	m_filter

Additional Inherited Members
Static Public Member Functions inherited from Kwave::StreamObject
static void	setInteractive (bool interactive)

Detailed Description

Definition at line 32 of file LowPassFilter.h.

Constructor & Destructor Documentation

LowPassFilter()

Kwave::LowPassFilter::LowPassFilter

(

)

Constructor

Definition at line 28 of file LowPassFilter.cpp.

References initFilter().

    :Kwave::SampleSource(Q_NULLPTR), m_buffer(blockSize()),
    m_f_cutoff(M_PI)
{
    initFilter();
}

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~LowPassFilter()

Kwave::LowPassFilter::~LowPassFilter ( )

virtual

Destructor

Definition at line 36 of file LowPassFilter.cpp.

{
}

Member Function Documentation

at()

double Kwave::LowPassFilter::at ( double  f )

virtual

See also

TransmissionFunction::at()

Implements Kwave::TransmissionFunction.

Definition at line 166 of file LowPassFilter.cpp.

References m_filter.

{
    /*
     * filter function as extracted from the aRts code:
     *
     * y[t] = cx*x[t] + cx1*x[t-1] + cx2*x[t-2]
     *                + cy1*y[t-1] + cy2*y[t-2];
     *
     * convert filter coefficients to our notation:
     */
    double a0, a1, a2, b1, b2;
    a0 = m_filter.cx;
    a1 = m_filter.cx1;
    a2 = m_filter.cx2;
    b1 = m_filter.cy1;
    b2 = m_filter.cy2;

    /*
     *        a0*z^2 + a1*z + a2
     * H(z) = ------------------   | z = e ^ (j*2*pi*f)
     *          z^2 - b1*z - b0
     */
    std::complex<double> h;
    std::complex<double> w;
    std::complex<double> j(0.0,1.0);
    std::complex<double> z;

    w = f;
    z = std::exp(j*w);

    // get h[z] at z=e^jw
    h = 0.95 * (a0 * (z*z) + (a1*z) + a2) / ((z*z) - (b1*z) - b2);

    return sqrt(std::norm(h));
}

goOn()

void Kwave::LowPassFilter::goOn ( )

virtual

does the calculation

Implements Kwave::SampleSource.

Definition at line 41 of file LowPassFilter.cpp.

References m_buffer, and output().

{
    emit output(m_buffer);
}

initFilter()

void Kwave::LowPassFilter::initFilter ( )

private

reset/initialize the filter coefficients

Definition at line 47 of file LowPassFilter.cpp.

References m_filter.

Referenced by LowPassFilter(), and setFrequency().

{
    m_filter.x1 = 0.0;
    m_filter.x2 = 0.0;
    m_filter.y1 = 0.0;
    m_filter.y2 = 0.0;
    m_filter.y  = 0.0;
}

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input

void Kwave::LowPassFilter::input ( Kwave::SampleArray  data )

slot

receives input data

Definition at line 138 of file LowPassFilter.cpp.

References double2sample(), m_buffer, m_f_cutoff, m_filter, normed_setfilter_shelvelowpass(), Kwave::SampleArray::resize(), sample2double(), and Kwave::SampleArray::size().

{
    const Kwave::SampleArray &in = data;
    bool ok = m_buffer.resize(in.size());
    Q_ASSERT(ok);
    Q_UNUSED(ok);

    normed_setfilter_shelvelowpass(m_f_cutoff);

    for (unsigned i = 0; i < in.size(); i++)
    {
        // do the filtering
        m_filter.x = sample2double(in[i]);
        m_filter.y =
            m_filter.cx  * m_filter.x  +
            m_filter.cx1 * m_filter.x1 +
            m_filter.cx2 * m_filter.x2 +
            m_filter.cy1 * m_filter.y1 +
            m_filter.cy2 * m_filter.y2;
        m_filter.x2 = m_filter.x1;
        m_filter.x1 = m_filter.x;
        m_filter.y2 = m_filter.y1;
        m_filter.y1 = m_filter.y;
        m_buffer[i] = double2sample(0.95 * m_filter.y);
    }
}

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normed_setfilter_shelvelowpass()

void Kwave::LowPassFilter::normed_setfilter_shelvelowpass ( double  freq )

private

calculate filter coefficients for a given frequency

Definition at line 121 of file LowPassFilter.cpp.

References m_filter, and shelve().

Referenced by input(), and setFrequency().

{
    double gain;
    double boost = 80.0;

    gain = pow(10.0, boost / 20.0);
    shelve(freq / (2 * M_PI), boost,
        &m_filter.cx, &m_filter.cx1, &m_filter.cx2,
        &m_filter.cy1, &m_filter.cy2);
    m_filter.cx  /= gain;
    m_filter.cx1 /= gain;
    m_filter.cx2 /= gain;
    m_filter.cy1  = -m_filter.cy1;
    m_filter.cy2  = -m_filter.cy2;
}

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output

void Kwave::LowPassFilter::output ( Kwave::SampleArray  data )

signal

emits a block with the filtered data

Referenced by goOn().

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setFrequency

void Kwave::LowPassFilter::setFrequency ( const QVariant  fc )

slot

Sets the cutoff frequency, normed to [0...2Pi]. The calculation is: fc = frequency [Hz] * 2 * Pi / f_sample [Hz]. The default setting is 0.5.

Definition at line 203 of file LowPassFilter.cpp.

References initFilter(), m_f_cutoff, and normed_setfilter_shelvelowpass().

Referenced by Kwave::LowPassDialog::updateDisplay().

{

    double new_freq = QVariant(fc).toDouble();
    if (qFuzzyCompare(new_freq, m_f_cutoff)) return; // nothing to do

    m_f_cutoff = new_freq;
    initFilter();
    normed_setfilter_shelvelowpass(m_f_cutoff);
}

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Member Data Documentation

cx

double Kwave::LowPassFilter::cx

Definition at line 85 of file LowPassFilter.h.

cx1

double Kwave::LowPassFilter::cx1

Definition at line 85 of file LowPassFilter.h.

cx2

double Kwave::LowPassFilter::cx2

Definition at line 85 of file LowPassFilter.h.

cy1

double Kwave::LowPassFilter::cy1

Definition at line 85 of file LowPassFilter.h.

cy2

double Kwave::LowPassFilter::cy2

Definition at line 85 of file LowPassFilter.h.

m_buffer

Kwave::SampleArray Kwave::LowPassFilter::m_buffer

private

buffer for input

Definition at line 78 of file LowPassFilter.h.

Referenced by goOn(), and input().

m_f_cutoff

double Kwave::LowPassFilter::m_f_cutoff

private

cutoff frequency [0...PI]

Definition at line 81 of file LowPassFilter.h.

Referenced by input(), and setFrequency().

m_filter

struct { ... } Kwave::LowPassFilter::m_filter

structure with the filter coefficients

Referenced by at(), initFilter(), input(), and normed_setfilter_shelvelowpass().

x

double Kwave::LowPassFilter::x

Definition at line 86 of file LowPassFilter.h.

x1

double Kwave::LowPassFilter::x1

Definition at line 86 of file LowPassFilter.h.

x2

double Kwave::LowPassFilter::x2

Definition at line 86 of file LowPassFilter.h.

y

double Kwave::LowPassFilter::y

Definition at line 86 of file LowPassFilter.h.

y1

double Kwave::LowPassFilter::y1

Definition at line 86 of file LowPassFilter.h.

y2

double Kwave::LowPassFilter::y2

Definition at line 86 of file LowPassFilter.h.

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

• plugins/lowpass/LowPassFilter.h
• plugins/lowpass/LowPassFilter.cpp