www.pudn.com > mp3rar.rar > tns.c

/************************* MPEG-2 NBC Audio Decoder ************************** 
 *                                                                           * 
"This software module was originally developed by  
AT&T, Dolby Laboratories, Fraunhofer Gesellschaft IIS in the course of  
development of the MPEG-2 NBC/MPEG-4 Audio standard ISO/IEC 13818-7,  
14496-1,2 and 3. This software module is an implementation of a part of one or more  
MPEG-2 NBC/MPEG-4 Audio tools as specified by the MPEG-2 NBC/MPEG-4  
Audio standard. ISO/IEC  gives users of the MPEG-2 NBC/MPEG-4 Audio  
standards free license to this software module or modifications thereof for use in  
hardware or software products claiming conformance to the MPEG-2 NBC/MPEG-4 
Audio  standards. Those intending to use this software module in hardware or  
software products are advised that this use may infringe existing patents.  
The original developer of this software module and his/her company, the subsequent  
editors and their companies, and ISO/IEC have no liability for use of this software  
module or modifications thereof in an implementation. Copyright is not released for  
non MPEG-2 NBC/MPEG-4 Audio conforming products.The original developer 
retains full right to use the code for his/her  own purpose, assign or donate the  
code to a third party and to inhibit third party from using the code for non  
MPEG-2 NBC/MPEG-4 Audio conforming products. This copyright notice must 
be included in all copies or derivative works."  
Copyright(c)1996. 
 *                                                                           * 
 ****************************************************************************/ 
#include "all.h" 
 
#define	sfb_offset(x) ( ((x) > 0) ? sfb_top[(x)-1] : 0 ) 
 
/* Decoder transmitted coefficients for one TNS filter */ 
void 
tns_decode_coef( int order, int coef_res, short *coef, Float *a ) 
{ 
    int i, m; 
    Float iqfac,  iqfac_m; 
    Float tmp[TNS_MAX_ORDER+1], b[TNS_MAX_ORDER+1]; 
 
    /* Inverse quantization */ 
    iqfac   = (float)(((1 << (coef_res-1)) - 0.5) / (C_PI/2.0)); 
    iqfac_m = (float)(((1 << (coef_res-1)) + 0.5) / (C_PI/2.0)); 
    for (i=0; i= 0) ? iqfac : iqfac_m) ); 
    } 
    /* Conversion to LPC coefficients 
     * Markel and Gray,  pg. 95 
     */ 
    a[0] = 1; 
    for (m=1; m<=order; m++)  { 
	b[0] = a[0]; 
	for (i=1; i0; j--) 
	    state[j] = state[j-1]; 
	state[0] = y; 
	*spec = y; 
	spec += inc; 
    } 
} 
 
/* TNS decoding for one channel and frame */ 
void 
tns_decode_subblock(Float *spec, int nbands, short *sfb_top, int islong, 
	TNSinfo *tns_info) 
{ 
    int f, m, start, stop, size, inc; 
    int n_filt, coef_res, order, direction; 
    short *coef; 
    Float lpc[TNS_MAX_ORDER+1]; 
    TNSfilt *filt; 
 
    n_filt = tns_info->n_filt; 
    for (f=0; fcoef_res; 
	filt = &tns_info->filt[f]; 
	order = filt->order; 
	direction = filt->direction; 
	coef = filt->coef; 
	start = filt->start_band; 
	stop = filt->stop_band; 
 
	m = tns_max_order(islong); 
	if (order > m) { 
//	    CommonWarning("Error in tns max order"); 
	    order = m; 
	} 
	if (!order)  continue; 
 
	tns_decode_coef( order, coef_res, coef, lpc ); 
 
	start = min(start, tns_max_bands(islong)); 
        start = min(start, nbands); 
	start = sfb_offset( start ); 
	 
	stop = min(stop, tns_max_bands(islong)); 
        stop = min(stop, nbands); 
	stop = sfb_offset( stop ); 
	if ((size = stop - start) <= 0)  continue; 
 
	if (direction)  { 
	    inc = -1; 
	}  else { 
	    inc =  1; 
	} 
 
	tns_ar_filter( &spec[start], size, inc, lpc, order ); 
    } 
}