// Kaiser-Bessel derived window
float liquid_kbd(unsigned int _n,
unsigned int _N,
float _beta)
{
// TODO add reference
// validate input
if (_n >= _N) {
fprintf(stderr,"error: liquid_kbd(), index exceeds maximum\n");
exit(1);
} else if (_N == 0) {
fprintf(stderr,"error: liquid_kbd(), window length must be greater than zero\n");
exit(1);
} else if ( _N % 2 ) {
fprintf(stderr,"error: liquid_kbd(), window length must be odd\n");
exit(1);
}
unsigned int M = _N / 2;
if (_n >= M)
return liquid_kbd(_N-_n-1,_N,_beta);
float w0 = 0.0f;
float w1 = 0.0f;
float w;
unsigned int i;
for (i=0; i<=M; i++) {
// compute Kaiser window
w = kaiser(i,M+1,_beta,0.0f);
// accumulate window sums
w1 += w;
if (i <= _n) w0 += w;
}
//printf("%12.8f / %12.8f = %12.8f\n", w0, w1, w0/w1);
return sqrtf(w0 / w1);
}
// create spgram object
// _nfft : FFT size
// _wtype : window type, e.g. LIQUID_WINDOW_HAMMING
// _window_len : window length
// _delay : delay between transforms, _delay > 0
SPGRAM() SPGRAM(_create)(unsigned int _nfft,
int _wtype,
unsigned int _window_len,
unsigned int _delay)
{
// validate input
if (_nfft < 2) {
fprintf(stderr,"error: spgram%s_create(), fft size must be at least 2\n", EXTENSION);
exit(1);
} else if (_window_len > _nfft) {
fprintf(stderr,"error: spgram%s_create(), window size cannot exceed fft size\n", EXTENSION);
exit(1);
} else if (_window_len == 0) {
fprintf(stderr,"error: spgram%s_create(), window size must be greater than zero\n", EXTENSION);
exit(1);
} else if (_wtype == LIQUID_WINDOW_KBD && _window_len % 2) {
fprintf(stderr,"error: spgram%s_create(), KBD window length must be even\n", EXTENSION);
exit(1);
} else if (_delay == 0) {
fprintf(stderr,"error: spgram%s_create(), delay must be greater than 0\n", EXTENSION);
exit(1);
}
// allocate memory for main object
SPGRAM() q = (SPGRAM()) malloc(sizeof(struct SPGRAM(_s)));
// set input parameters
q->nfft = _nfft;
q->wtype = _wtype;
q->window_len = _window_len;
q->delay = _delay;
q->frequency = 0;
q->sample_rate= -1;
// set object for full accumulation
SPGRAM(_set_alpha)(q, -1.0f);
// create FFT arrays, object
q->buf_time = (TC*) malloc((q->nfft)*sizeof(TC));
q->buf_freq = (TC*) malloc((q->nfft)*sizeof(TC));
q->psd = (T *) malloc((q->nfft)*sizeof(T ));
q->fft = FFT_CREATE_PLAN(q->nfft, q->buf_time, q->buf_freq, FFT_DIR_FORWARD, FFT_METHOD);
// create buffer
q->buffer = WINDOW(_create)(q->window_len);
// create window
q->w = (T*) malloc((q->window_len)*sizeof(T));
unsigned int i;
unsigned int n = q->window_len;
float beta = 10.0f;
float zeta = 3.0f;
for (i=0; i<n; i++) {
switch (q->wtype) {
case LIQUID_WINDOW_HAMMING: q->w[i] = hamming(i,n); break;
case LIQUID_WINDOW_HANN: q->w[i] = hann(i,n); break;
case LIQUID_WINDOW_BLACKMANHARRIS: q->w[i] = blackmanharris(i,n); break;
case LIQUID_WINDOW_BLACKMANHARRIS7: q->w[i] = blackmanharris7(i,n); break;
case LIQUID_WINDOW_KAISER: q->w[i] = kaiser(i,n,beta,0); break;
case LIQUID_WINDOW_FLATTOP: q->w[i] = flattop(i,n); break;
case LIQUID_WINDOW_TRIANGULAR: q->w[i] = triangular(i,n,n); break;
case LIQUID_WINDOW_RCOSTAPER: q->w[i] = liquid_rcostaper_windowf(i,n/3,n); break;
case LIQUID_WINDOW_KBD: q->w[i] = liquid_kbd(i,n,zeta); break;
default:
fprintf(stderr,"error: spgram%s_create(), invalid window\n", EXTENSION);
exit(1);
}
}
// scale by window magnitude, FFT size
float g = 0.0f;
for (i=0; i<q->window_len; i++)
g += q->w[i] * q->w[i];
g = M_SQRT2 / ( sqrtf(g / q->window_len) * sqrtf((float)(q->nfft)) );
// scale window and copy
for (i=0; i<q->window_len; i++)
q->w[i] = g * q->w[i];
// reset the spgram object
q->num_samples_total = 0;
q->num_transforms_total = 0;
SPGRAM(_reset)(q);
// return new object
return q;
}
