butterworth.h

/* ======== IGeoS ===== Distribition full ===== IGeoS =========
**                                                                         
** butterworth.h: Created by 'AMSS-developer' on Fri Jan 12 19:49:03 2018
**                                                                         
** Product      : IGeoS - Integrated Geoscience Software
**                                                                         
** Description  : System for seismic, well log, and potential-field data analysis
**                                                                         
** =================== Limited License: ===================================
** 
** This software is provided free under the following terms and conditions:
** 
** 1. Permission to use, copy, and modify this software 
** for non-commercial purposes without fee is hereby granted, provided  
** that this copyright notice, the warranty disclaimer, and this
** permission notice appear in all copies.
** 
** 2. Distribution of this software or any part of it "bundled" in with
** any product is considered to be a 'commercial purpose'.
** 
** 3. Any new or adapted code developed to operate as a part of this
** software shall be contributed to the authors and distributed under
** the same license.
** 
** ================== Warranty Disclaimer: ================================
** 
** This software is provided "as is", with no support and without
** obligation on the part of the author to assist in its use, correction,
** modification, or enhancement. No guarantees or warranties,
** either express or implied, and regarding the accuracy, safety, or
** fitness for any particular purpose are provided by any contributor
** to this software package.
** 
** ======== IGeoS ===== Distribition full ===== IGeoS ========= */

/******** Butterworth filters derived from Seismic UNIX *******************/

/* Copyright (c) Colorado School of Mines, 1997.*/
/* All rights reserved.                       */

/*********************** self documentation **********************/
/*****************************************************************************
BUTTERWORTH - Functions to design and apply Butterworth filters:

FILTER_bfdesign         design a Butterworth filter
FILTER_bfhighpass       apply a high-pass Butterworth filter 
FILTER_bflowpass        apply a low-pass Butterworth filter 

******************************************************************************
Function Prototypes:
*/

void FILTER_bfhighpass (int npoles, DATA_SAMPLE f3db, int n, 
                DATA_SAMPLE p[], DATA_SAMPLE q[]);
void FILTER_bflowpass (int npoles, DATA_SAMPLE f3db, int n, 
                DATA_SAMPLE p[], DATA_SAMPLE q[]);
void FILTER_bfdesign (DATA_SAMPLE fpass, DATA_SAMPLE apass, 
                DATA_SAMPLE fstop, DATA_SAMPLE astop,
                int *npoles, DATA_SAMPLE *f3db);

/*
******************************************************************************
FILTER_bfdesign:
Input:
fpass           frequency in pass band at which amplitude is >= apass
apass           amplitude in pass band corresponding to frequency fpass
fstop           frequency in stop band at which amplitude is <= astop
astop           amplitude in stop band corresponding to frequency fstop

Output:
npoles          number of poles
f3db            frequency at which amplitude is sqrt(0.5) (-3 db)

FILTER_bfhighpass and FILTER_bflowpass:
Input:
npoles          number of poles (and zeros); npoles>=0 is required
f3db            3 db frequency; nyquist = 0.5; 0.0<=f3db<=0.5 is required
n               length of p and q
p               array[n] to be filtered

Output:
q               filtered array[n] (may be equivalent to p)

******************************************************************************
Notes:
(1) Nyquist frequency equals 0.5

(2) The following conditions must be true:
        (0.0<fpass && fpass<0.5) &&
        (0.0<fstop && fstop<0.5) &&
        (fpass!=fstop) &&
        (0.0<astop && astop<apass && apass<1.0)

(3) if (fpass<fstop)

FILTER_bfdesign:
Butterworth filter:  compute number of poles and -3 db frequency
for a low-pass or high-pass filter, given a frequency response
constrained at two frequencies.

******************************************************************************
Author:  Dave Hale, Colorado School of Mines, 06/02/89
*****************************************************************************/
/**************** end self doc ********************************/

---