powspec.c

ears-0.32, linux下有用的语音信号处理工具包

/************************************************************************
 *                                                                       *
 *               ROUTINES IN THIS FILE:                                  *
 *                                                                       *
 *                         powspec(): compute some kind of power         *
 *                                    spectrum                           *
 *                                                                       *
 ************************************************************************/

#include <stdio.h>
#include "others/mymath.h"
#include "rasta.h"
#include "functions.h"

/*
 *	This is the file that would get hacked and replaced if
 *	you want to change the basic pre-PLP spectral
 * 	analysis. In original form, it calls the usual
 *	ugly but efficient FFT routine that was translated
 *	from Fortran, and computes a simple power spectrum.
 *	A pointer to the fvec structure (float vector plus length) holding
 *	this computed array is returned to the calling program.
 *
 *	This routine departs from the usual form of allocating only on
 *	the first time it is called, since we wish to allow
 *	for calling it with different frame lengths at some future time.
 *	This means that new memory is allocated for every frame.
 *	To keep this amount from mounting up too badly, we free
 *	the space for the last frame each time through.
 */
struct fvec *powspec( const struct param *pptr, struct fvec *fptr)
{
	int i, fftlength, log2length;
	char *funcname;
	static struct fvec *pspecptr = NULL;
	float noise;

	funcname = "powspec";

	if(pspecptr != (struct fvec *)NULL)
	{
		/* Better not allocate pspecptr->values anywhere but 
			in this routine */
		free( pspecptr->values );
		free( pspecptr );
	}

        /* Round up */
	log2length = ceil(log((double)(fptr->length))/log(2.0));

	fftlength = two_to_the((double)log2length);
	pspecptr = alloc_fvec ( (fftlength / 2) + 1);
		/* Allow space for pspec from bin 0 through bin N/2 */

	/* Not currently checking array bounds for fft;
		since we pass the input length, we know that
		we are not reading from outside of the array.
		The power spectral routine should not write past
		the fftlength/2 + 1 . */
		
	fft_pow( fptr->values, pspecptr->values, 
			(long)fptr->length, (long) log2length );

	if(pptr->smallmask == TRUE)
	{
		noise = (float)fptr->length;
			/* adding the length of the data vector
			to each power spectral value is roughly
			like adding a random least significant
	        	 bit to the data, (differing only
			because of window and powspeclength not
			being exactly the same as data length)
			but is less computaton
			than calling random() many times. */
		for(i=0; i<pspecptr->length; i++)
		{
			pspecptr->values[i] += noise;
		}
	}


	return( pspecptr );
}