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/* -*- 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 program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version. See the file
COPYING included with this distribution for more information.
*/
#include "DecimatorB.h"
#include "maths/MathUtilities.h"
#include <iostream>
using std::vector;
DecimatorB::DecimatorB(int inLength, int decFactor)
{
m_inputLength = 0;
m_outputLength = 0;
m_decFactor = 1;
m_aaBuffer = 0;
m_tmpBuffer = 0;
initialise(inLength, decFactor);
}
DecimatorB::~DecimatorB()
{
deInitialise();
}
void DecimatorB::initialise(int inLength, int decFactor)
{
m_inputLength = inLength;
m_decFactor = decFactor;
m_outputLength = m_inputLength / m_decFactor;
if (m_decFactor < 2 || !MathUtilities::isPowerOfTwo(m_decFactor)) {
std::cerr << "ERROR: DecimatorB::initialise: Decimation factor must be a power of 2 and at least 2 (was: " << m_decFactor << ")" << std::endl;
m_decFactor = 0;
return;
}
if (m_inputLength % m_decFactor != 0) {
std::cerr << "ERROR: DecimatorB::initialise: inLength must be a multiple of decimation factor (was: " << m_inputLength << ", factor is " << m_decFactor << ")" << std::endl;
m_decFactor = 0;
return;
}
m_aaBuffer = new double[m_inputLength];
m_tmpBuffer = new double[m_inputLength];
// Order 6 Butterworth lowpass filter
// Calculated using e.g. MATLAB butter(6, 0.5, 'low')
m_b[0] = 0.029588223638661;
m_b[1] = 0.177529341831965;
m_b[2] = 0.443823354579912;
m_b[3] = 0.591764472773216;
m_b[4] = 0.443823354579912;
m_b[5] = 0.177529341831965;
m_b[6] = 0.029588223638661;
m_a[0] = 1.000000000000000;
m_a[1] = 0.000000000000000;
m_a[2] = 0.777695961855673;
m_a[3] = 0.000000000000000;
m_a[4] = 0.114199425062434;
m_a[5] = 0.000000000000000;
m_a[6] = 0.001750925956183;
for (int factor = m_decFactor; factor > 1; factor /= 2) {
m_o.push_back(vector<double>(6, 0.0));
}
}
void DecimatorB::deInitialise()
{
delete [] m_aaBuffer;
delete [] m_tmpBuffer;
}
void DecimatorB::doAntiAlias(const double *src, double *dst, int length,
int filteridx)
{
vector<double> &o = m_o[filteridx];
for (int i = 0; i < length; i++) {
double input = src[i];
double output = input * m_b[0] + o[0];
o[0] = input * m_b[1] - output * m_a[1] + o[1];
o[1] = input * m_b[2] - output * m_a[2] + o[2];
o[2] = input * m_b[3] - output * m_a[3] + o[3];
o[3] = input * m_b[4] - output * m_a[4] + o[4];
o[4] = input * m_b[5] - output * m_a[5] + o[5];
o[5] = input * m_b[6] - output * m_a[6];
dst[i] = output;
}
}
void DecimatorB::doProcess()
{
int filteridx = 0;
int factorDone = 1;
while (factorDone < m_decFactor) {
doAntiAlias(m_tmpBuffer, m_aaBuffer,
m_inputLength / factorDone,
filteridx);
filteridx ++;
factorDone *= 2;
for (int i = 0; i < m_inputLength / factorDone; ++i) {
m_tmpBuffer[i] = m_aaBuffer[i * 2];
}
}
}
void DecimatorB::process(const double *src, double *dst)
{
if (m_decFactor == 0) return;
for (int i = 0; i < m_inputLength; ++i) {
m_tmpBuffer[i] = src[i];
}
doProcess();
for (int i = 0; i < m_outputLength; ++i) {
dst[i] = m_tmpBuffer[i];
}
}
void DecimatorB::process(const float *src, float *dst)
{
if (m_decFactor == 0) return;
for (int i = 0; i < m_inputLength; ++i) {
m_tmpBuffer[i] = src[i];
}
doProcess();
for (int i = 0; i < m_outputLength; ++i) {
dst[i] = m_tmpBuffer[i];
}
}
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