kaiser.h

著名的 helix realplayer 基于手机 symbian 系统的 播放器全套源代码

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#ifndef _KAISER_H_
#define _KAISER_H_

/*
 * KaiserEstim() estimates the window length and beta needed to
 * meet the given filter specifications.
 *
 * fpass, fstop are normalized freq (1.0 == Nyquist).
 * atten is stopband attenuation in dB.
 */
void
KaiserEstim(float fpass, float fstop, float atten, int *length, float *beta) ;

/*
 *             inf
 * Io(x) = 1 + sum(((x/2)^r / r!)^2)
 *             r=1
 */
double
Izero(double x) ;

/*
 * KaiserLowpass() creates a Kaiser-windowed lowpass filter.
 *
 * length is length of filter wing.
 * cutoff is normalized cutoff freq (-6dB down).
 * beta is the Kaiser window parameter.
 * gain is the desired dc gain.
 *
 * The Kaiser window is given by:
 * w[n] = Io(beta * sqrt(1 - (n/M)^2)) / Io(beta)	(0 <= n <= M)
 *
 * Note: sampling of the "analog" lowpass is offset by 0.5 sample,
 * so that all phases are an even length.
 */
void 
KaiserLowpass(int length, float cutoff, float beta, float gain, double *filter) ;

#endif /* _KAISER_H_ */