// create arbitrary resampler
// _rate : resampling rate
// _m : prototype filter semi-length
// _fc : prototype filter cutoff frequency, fc in (0, 0.5)
// _As : prototype filter stop-band attenuation [dB] (e.g. 60)
// _npfb : number of filters in polyphase filterbank
RESAMP() RESAMP(_create)(float _rate,
unsigned int _m,
float _fc,
float _As,
unsigned int _npfb)
{
// validate input
if (_rate <= 0) {
fprintf(stderr,"error: resamp_%s_create(), resampling rate must be greater than zero\n", EXTENSION_FULL);
exit(1);
} else if (_m == 0) {
fprintf(stderr,"error: resamp_%s_create(), filter semi-length must be greater than zero\n", EXTENSION_FULL);
exit(1);
} else if (_fc <= 0.0f || _fc >= 0.5f) {
fprintf(stderr,"error: resamp_%s_create(), filter cutoff must be in (0,0.5)\n", EXTENSION_FULL);
exit(1);
} else if (_As <= 0.0f) {
fprintf(stderr,"error: resamp_%s_create(), filter stop-band suppression must be greater than zero\n", EXTENSION_FULL);
exit(1);
} else if (_npfb == 0) {
fprintf(stderr,"error: resamp_%s_create(), number of filter banks must be greater than zero\n", EXTENSION_FULL);
exit(1);
}
// allocate memory for resampler
RESAMP() q = (RESAMP()) malloc(sizeof(struct RESAMP(_s)));
// set rate using formal method (specifies output stride
// value 'del')
RESAMP(_set_rate)(q, _rate);
// set properties
q->m = _m; // prototype filter semi-length
q->fc = _fc; // prototype filter cutoff frequency
q->As = _As; // prototype filter stop-band attenuation
q->npfb = _npfb; // number of filters in bank
// design filter
unsigned int n = 2*q->m*q->npfb+1;
float hf[n];
TC h[n];
liquid_firdes_kaiser(n,q->fc/((float)(q->npfb)),q->As,0.0f,hf);
// normalize filter coefficients by DC gain
unsigned int i;
float gain=0.0f;
for (i=0; i<n; i++)
gain += hf[i];
gain = (q->npfb)/(gain);
// copy to type-specific array, applying gain
for (i=0; i<n; i++)
h[i] = hf[i]*gain;
q->f = FIRPFB(_create)(q->npfb,h,n-1);
// reset object and return
RESAMP(_reset)(q);
return q;
}
// create arbitrary resampler object with a specified input
// resampling rate and default parameters
// m (filter semi-length) = 7
// fc (filter cutoff frequency) = 0.25
// As (filter stop-band attenuation) = 60 dB
// npfb (number of filters in the bank) = 64
RESAMP() RESAMP(_create_default)(float _rate)
{
// validate input
if (_rate <= 0) {
fprintf(stderr,"error: resamp_%s_create_default(), resampling rate must be greater than zero\n", EXTENSION_FULL);
exit(1);
}
// det default parameters
unsigned int m = 7;
float fc = 0.5f*_rate > 0.49f ? 0.49f : 0.5f*_rate;
float As = 60.0f;
unsigned int npfb = 64;
// create and return resamp object
return RESAMP(_create)(_rate, m, fc, As, npfb);
}
#include <stdlib.h>
#include <string.h>
#include <math.h>
// defined:
// TO output data type
// TC coefficient data type
// TI input data type
// RESAMP() name-mangling macro
// FIRPFB() firpfb macro
// enable run-time debug printing of resampler
#define DEBUG_RESAMP_PRINT 0
// internal: update timing
void RESAMP(_update_timing_state)(RESAMP() _q);
struct RESAMP(_s) {
// filter design parameters
unsigned int m; // filter semi-length, h_len = 2*m + 1
float As; // filter stop-band attenuation
float fc; // filter cutoff frequency
// resampling properties/states
float rate; // resampling rate (ouput/input)
float del; // fractional delay step
// floating-point phase
float tau; // accumulated timing phase, 0 <= tau < 1
float bf; // soft filterbank index, bf = tau*npfb = b + mu
int b; // base filterbank index, 0 <= b < npfb
RESAMP() RESAMP(_create)(float _r,
unsigned int _h_len,
float _fc,
float _As,
unsigned int _npfb)
{
// validate input
if (_r <= 0) {
fprintf(stderr,"error: resamp_%s_create(), resampling rate must be greater than zero\n", EXTENSION_FULL);
exit(1);
} else if (_h_len == 0) {
fprintf(stderr,"error: resamp_%s_create(), filter length must be greater than zero\n", EXTENSION_FULL);
exit(1);
} else if (_npfb == 0) {
fprintf(stderr,"error: resamp_%s_create(), number of filter banks must be greater than zero\n", EXTENSION_FULL);
exit(1);
} else if (_fc <= 0.0f || _fc >= 0.5f) {
fprintf(stderr,"error: resamp_%s_create(), filter cutoff must be in (0,0.5)\n", EXTENSION_FULL);
exit(1);
} else if (_As <= 0.0f) {
fprintf(stderr,"error: resamp_%s_create(), filter stop-band suppression must be greater than zero\n", EXTENSION_FULL);
exit(1);
}
RESAMP() q = (RESAMP()) malloc(sizeof(struct RESAMP(_s)));
q->r = _r;
q->As = _As;
q->fc = _fc;
q->h_len = _h_len;
q->b = 0;
q->del = 1.0f / q->r;
#if RESAMP_USE_FIXED_POINT_PHASE
q->num_bits_npfb = liquid_nextpow2(_npfb);
q->npfb = 1<<q->num_bits_npfb;
q->num_bits_phase = 20;
q->max_phase = 1 << q->num_bits_phase;
q->num_shift_bits = q->num_bits_phase - q->num_bits_npfb;
q->theta = 0;
q->d_theta = (unsigned int)( q->max_phase * q->del );
#else
q->npfb = _npfb;
q->tau = 0.0f;
q->bf = 0.0f;
#endif
// design filter
unsigned int n = 2*_h_len*q->npfb+1;
float hf[n];
TC h[n];
liquid_firdes_kaiser(n,q->fc/((float)(q->npfb)),q->As,0.0f,hf);
// normalize filter coefficients by DC gain
unsigned int i;
float gain=0.0f;
for (i=0; i<n; i++)
gain += hf[i];
gain = (q->npfb)/(gain);
// copy to type-specific array
for (i=0; i<n; i++)
h[i] = hf[i]*gain;
q->f = FIRPFB(_create)(q->npfb,h,n-1);
//for (i=0; i<n; i++)
// PRINTVAL_TC(h[i],%12.8f);
//exit(0);
return q;
}
gain += hf[i];
gain = (q->npfb)/(gain);
// copy to type-specific array
for (i=0; i<n; i++)
h[i] = hf[i]*gain;
q->f = FIRPFB(_create)(q->npfb,h,n-1);
//for (i=0; i<n; i++)
// PRINTVAL_TC(h[i],%12.8f);
//exit(0);
return q;
}
void RESAMP(_destroy)(RESAMP() _q)
{
FIRPFB(_destroy)(_q->f);
free(_q);
}
void RESAMP(_print)(RESAMP() _q)
{
printf("resampler [rate: %f]\n", _q->r);
FIRPFB(_print)(_q->f);
}
void RESAMP(_reset)(RESAMP() _q)
{
FIRPFB(_clear)(_q->f);
_q->b = 0;
// create msresamp object
// TODO: add signal bandwidth parameter?
// TODO: add center frequency parameter; facilitates DDS object synthesis
// _r : resampling rate [output/input]
// _As : stop-band attenuation
MSRESAMP() MSRESAMP(_create)(float _r,
float _As)
{
// validate input
if (_r <= 0.0f) {
fprintf(stderr,"error: msresamp_%s_create(), resampling rate must be greater than zero\n", EXTENSION_FULL);
exit(1);
}
// create object
MSRESAMP() q = (MSRESAMP()) malloc(sizeof(struct MSRESAMP(_s)));
// set internal properties
q->rate = _r; // composite rate
q->As = _As; // stop-band suppression
// decimation or interpolation?
q->type = (q->rate > 1.0f) ? LIQUID_RESAMP_INTERP : LIQUID_RESAMP_DECIM;
// compute derived values
q->rate_arbitrary = q->rate;
q->rate_halfband = 1.0f;
q->num_halfband_stages = 0;
switch(q->type) {
case LIQUID_RESAMP_INTERP:
while (q->rate_arbitrary > 2.0f) {
q->num_halfband_stages++;
q->rate_halfband *= 2.0f;
q->rate_arbitrary *= 0.5f;
}
break;
case LIQUID_RESAMP_DECIM:
while (q->rate_arbitrary < 0.5f) {
q->num_halfband_stages++;
q->rate_halfband *= 0.5f;
q->rate_arbitrary *= 2.0f;
}
break;
default:;
}
// allocate memory for buffer
q->buffer_len = 4 + (1 << q->num_halfband_stages);
q->buffer = (T*) malloc( q->buffer_len*sizeof(T) );
// create single multi-stage half-band resampler object
// TODO: compute appropriate cut-off frequency
q->halfband_resamp = MSRESAMP2(_create)(q->type,
q->num_halfband_stages,
0.4f, 0.0f, q->As);
// create arbitrary resampler object
// TODO: compute appropriate parameters
q->arbitrary_resamp = RESAMP(_create)(q->rate_arbitrary, 7, 0.4f, q->As, 64);
// reset object
MSRESAMP(_reset)(q);
// return main object
return q;
}
