/*
* design and implementation of different types of digital filters
*
* Copyright (C) 2001 Anders Johansson ajh@atri.curtin.edu.au
*
* This file is part of mpv.
*
* mpv 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.
*
* mpv is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with mpv. If not, see .
*/
#include
#include
#include "dsp.h"
/******************************************************************************
* FIR filter implementations
******************************************************************************/
/* C implementation of FIR filter y=w*x
n number of filter taps, where mod(n,4)==0
w filter taps
x input signal must be a circular buffer which is indexed backwards
*/
inline FLOAT_TYPE af_filter_fir(register unsigned int n, const FLOAT_TYPE* w,
const FLOAT_TYPE* x)
{
register FLOAT_TYPE y; // Output
y = 0.0;
do{
n--;
y+=w[n]*x[n];
}while(n != 0);
return y;
}
/******************************************************************************
* FIR filter design
******************************************************************************/
/* Design FIR filter using the Window method
n filter length must be odd for HP and BS filters
w buffer for the filter taps (must be n long)
fc cutoff frequencies (1 for LP and HP, 2 for BP and BS)
0 < fc < 1 where 1 <=> Fs/2
flags window and filter type as defined in filter.h
variables are ored together: i.e. LP|HAMMING will give a
low pass filter designed using a hamming window
opt beta constant used only when designing using kaiser windows
returns 0 if OK, -1 if fail
*/
int af_filter_design_fir(unsigned int n, FLOAT_TYPE* w, const FLOAT_TYPE* fc,
unsigned int flags, FLOAT_TYPE opt)
{
unsigned int o = n & 1; // Indicator for odd filter length
unsigned int end = ((n + 1) >> 1) - o; // Loop end
unsigned int i; // Loop index
FLOAT_TYPE k1 = 2 * M_PI; // 2*pi*fc1
FLOAT_TYPE k2 = 0.5 * (FLOAT_TYPE)(1 - o);// Constant used if the filter has even length
FLOAT_TYPE k3; // 2*pi*fc2 Constant used in BP and BS design
FLOAT_TYPE g = 0.0; // Gain
FLOAT_TYPE t1,t2,t3; // Temporary variables
FLOAT_TYPE fc1,fc2; // Cutoff frequencies
// Sanity check
if(!w || (n == 0)) return -1;
// Get window coefficients
switch(flags & WINDOW_MASK){
case(BOXCAR):
af_window_boxcar(n,w); break;
case(TRIANG):
af_window_triang(n,w); break;
case(HAMMING):
af_window_hamming(n,w); break;
case(HANNING):
af_window_hanning(n,w); break;
case(BLACKMAN):
af_window_blackman(n,w); break;
case(FLATTOP):
af_window_flattop(n,w); break;
case(KAISER):
af_window_kaiser(n,w,opt); break;
default:
return -1;
}
if(flags & (LP | HP)){
fc1=*fc;
// Cutoff frequency must be < 0.5 where 0.5 <=> Fs/2
fc1 = ((fc1 <= 1.0) && (fc1 > 0.0)) ? fc1/2 : 0.25;
k1 *= fc1;
if(flags & LP){ // Low pass filter
// If the filter length is odd, there is one point which is exactly
// in the middle. The value at this point is 2*fCutoff*sin(x)/x,
// where x is zero. To make sure nothing strange happens, we set this
// value separately.
if (o){
w[end] = fc1 * w[end] * 2.0;
g=w[end];
}
// Create filter
for (i=0 ; i Fs/2
fc1 = ((fc1 <= 1.0) && (fc1 > 0.0)) ? fc1/2 : 0.25;
fc2 = ((fc2 <= 1.0) && (fc2 > 0.0)) ? fc2/2 : 0.25;
k3 = k1 * fc2; // 2*pi*fc2
k1 *= fc1; // 2*pi*fc1
if(flags & BP){ // Band pass
// Calculate center tap
if (o){
g=w[end]*(fc1+fc2);
w[end] = (fc2 - fc1) * w[end] * 2.0;
}
// Create filter
for (i=0 ; i1000.0 || Q< 1.0))
return -1;
memcpy(at,a,3*sizeof(FLOAT_TYPE));
memcpy(bt,b,3*sizeof(FLOAT_TYPE));
bt[1]/=Q;
/* Calculate a and b and overwrite the original values */
af_filter_prewarp(at, fc, fs);
af_filter_prewarp(bt, fc, fs);
/* Execute bilinear transform */
af_filter_bilinear(at, bt, k, fs, coef);
return 0;
}