annotate dsp/rateconversion/Decimator.cpp @ 22:f7edcd9138bd

* Add decimation filter for 8x decimation

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    QM DSP Library

    Centre for Digital Music, Queen Mary, University of London.
    This file copyright 2005-2006 Christian Landone.
    All rights reserved.
*/

#include "Decimator.h"

#include <iostream>

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

Decimator::Decimator( unsigned int inLength, unsigned int decFactor )
{

    m_inputLength = 0;
    m_outputLength = 0;
    m_decFactor = 1;

    initialise( inLength, decFactor );
}

Decimator::~Decimator()
{
    deInitialise();
}

void Decimator::initialise( unsigned int inLength, unsigned int decFactor)
{
    m_inputLength = inLength;
    m_decFactor = decFactor;
    m_outputLength = m_inputLength / m_decFactor;

    decBuffer = new double[ m_inputLength ];

    // If adding new factors here, add them to
    // getHighestSupportedFactor in the header as well

    if(m_decFactor == 8)
    {
        //////////////////////////////////////////////////
        b[0] = 0.060111378492136;
        b[1] = -0.257323420830598;
        b[2] = 0.420583503165928;
        b[3] = -0.222750785197418;
        b[4] = -0.222750785197418;
        b[5] = 0.420583503165928;
        b[6] = -0.257323420830598;
        b[7] = 0.060111378492136;

        a[0] = 1;
        a[1] = -5.667654878577432;
        a[2] = 14.062452278088417;
        a[3] = -19.737303840697738;
        a[4] = 16.889698874608641;
        a[5] = -8.796600612325928;
        a[6] = 2.577553446979888;
        a[7] = -0.326903916815751;
        //////////////////////////////////////////////////
    }
    else if( m_decFactor == 4 )
    {
	//////////////////////////////////////////////////
	b[ 0 ] = 0.10133306904918619;
	b[ 1 ] = -0.2447523353702363;
	b[ 2 ] = 0.33622528590120965;
	b[ 3 ] = -0.13936581560633518;
	b[ 4 ] = -0.13936581560633382;
	b[ 5 ] = 0.3362252859012087;
	b[ 6 ] = -0.2447523353702358;
	b[ 7 ] = 0.10133306904918594;

	a[ 0 ] = 1;
	a[ 1 ] = -3.9035590278139427;
	a[ 2 ] = 7.5299379980621133;
	a[ 3 ] = -8.6890803793177511;
	a[ 4 ] = 6.4578667096099176;
	a[ 5 ] = -3.0242979431223631;
	a[ 6 ] = 0.83043385136748382;
	a[ 7 ] = -0.094420800837809335;
	//////////////////////////////////////////////////
    }
    else if( m_decFactor == 2 )
    {
	//////////////////////////////////////////////////
	b[ 0 ] = 0.20898944260075727;
	b[ 1 ] = 0.40011234879814367;
	b[ 2 ] = 0.819741973072733;
	b[ 3 ] = 1.0087419911682323;
	b[ 4 ] = 1.0087419911682325;
	b[ 5 ] = 0.81974197307273156;
	b[ 6 ] = 0.40011234879814295;
	b[ 7 ] = 0.20898944260075661;

	a[ 0 ] = 1;
	a[ 1 ] = 0.0077331184208358217;
	a[ 2 ] = 1.9853971155964376;
	a[ 3 ] = 0.19296739275341004;
	a[ 4 ] = 1.2330748872852182;
	a[ 5 ] = 0.18705341389316466;
	a[ 6 ] = 0.23659265908013868;
	a[ 7 ] = 0.032352924250533946;
    }
    else
    {
        if ( m_decFactor != 1 ) {
            std::cerr << "WARNING: Decimator::initialise: unsupported decimation factor " << m_decFactor << ", no antialiasing filter will be used" << std::endl;
        }

	//////////////////////////////////////////////////
	b[ 0 ] = 1;
	b[ 1 ] = 0;
	b[ 2 ] = 0;
	b[ 3 ] = 0;
	b[ 4 ] = 0;
	b[ 5 ] = 0;
	b[ 6 ] = 0;
	b[ 7 ] = 0;

	a[ 0 ] = 1;
	a[ 1 ] = 0;
	a[ 2 ] = 0;
	a[ 3 ] = 0;
	a[ 4 ] = 0;
	a[ 5 ] = 0;
	a[ 6 ] = 0;
	a[ 7 ] = 0;
    }

    resetFilter();
}

void Decimator::deInitialise()
{
    delete [] decBuffer;
}

void Decimator::resetFilter()
{
    Input = Output = 0;

    o1=o2=o3=o4=o5=o6=o7=0;
}

void Decimator::doAntiAlias(const double *src, double *dst, unsigned int length)
{

    for( unsigned int i = 0; i < length; i++ )
    {
	Input = (double)src[ i ];

	Output = Input * b[ 0 ] + o1;

	o1 = Input * b[ 1 ] - Output * a[ 1 ] + o2;
	o2 = Input * b[ 2 ] - Output * a[ 2 ] + o3;
	o3 = Input * b[ 3 ] - Output * a[ 3 ] + o4;
	o4 = Input * b[ 4 ] - Output * a[ 4 ] + o5;
	o5 = Input * b[ 5 ] - Output * a[ 5 ] + o6;
	o6 = Input * b[ 6 ] - Output * a[ 6 ] + o7;
	o7 = Input * b[ 7 ] - Output * a[ 7 ] ;

	dst[ i ] = Output;
    }

}

void Decimator::process(const double *src, double *dst)
{
    if( m_decFactor != 1 )
    {
	doAntiAlias( src, decBuffer, m_inputLength );
    }
    unsigned idx = 0;

    for( unsigned int i = 0; i < m_outputLength; i++ )
    {
	dst[ idx++ ] = decBuffer[ m_decFactor * i ];
    }
}