biquad.h

00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * biquad.h - General telephony bi-quad section routines (currently this just
00005  *            handles canonic/type 2 form)
00006  *
00007  * Written by Steve Underwood <steveu@coppice.org>
00008  *
00009  * Copyright (C) 2001 Steve Underwood
00010  *
00011  * All rights reserved.
00012  *
00013  * This program is free software; you can redistribute it and/or modify
00014  * it under the terms of the GNU Lesser General Public License version 2.1,
00015  * as published by the Free Software Foundation.
00016  *
00017  * This program is distributed in the hope that it will be useful,
00018  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00019  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00020  * GNU Lesser General Public License for more details.
00021  *
00022  * You should have received a copy of the GNU Lesser General Public
00023  * License along with this program; if not, write to the Free Software
00024  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
00025  *
00026  * $Id: biquad.h,v 1.14 2008/04/17 14:26:59 steveu Exp $
00027  */
00028 
00029 /*! \page biquad_page Bi-quadratic filter sections
00030 \section biquad_page_sec_1 What does it do?
00031 ???.
00032 
00033 \section biquad_page_sec_2 How does it work?
00034 ???.
00035 */
00036 
00037 #if !defined(_SPANDSP_BIQUAD_H_)
00038 #define _SPANDSP_BIQUAD_H_
00039 
00040 typedef struct
00041 {
00042     int32_t gain;
00043     int32_t a1;
00044     int32_t a2;
00045     int32_t b1;
00046     int32_t b2;
00047 
00048     int32_t z1;
00049     int32_t z2;
00050 
00051 #if FIRST_ORDER_NOISE_SHAPING
00052     int32_t residue;
00053 #elif SECOND_ORDER_NOISE_SHAPING
00054     int32_t residue1;
00055     int32_t residue2;
00056 #endif
00057 } biquad2_state_t;
00058 
00059 #if defined(__cplusplus)
00060 extern "C"
00061 {
00062 #endif
00063 
00064 static __inline__ void biquad2_init(biquad2_state_t *bq,
00065                                     int32_t gain,
00066                                     int32_t a1,
00067                                     int32_t a2,
00068                                     int32_t b1,
00069                                     int32_t b2)
00070 {
00071     bq->gain = gain;
00072     bq->a1 = a1;
00073     bq->a2 = a2;
00074     bq->b1 = b1;
00075     bq->b2 = b2;
00076     
00077     bq->z1 = 0;
00078     bq->z2 = 0;    
00079 
00080 #if FIRST_ORDER_NOISE_SHAPING
00081     bq->residue = 0;
00082 #elif SECOND_ORDER_NOISE_SHAPING
00083     bq->residue1 = 0;
00084     bq->residue2 = 0;
00085 #endif
00086 }
00087 /*- End of function --------------------------------------------------------*/
00088 
00089 static __inline__ int16_t biquad2(biquad2_state_t *bq, int16_t sample)
00090 {
00091     int32_t y;
00092     int32_t z0;
00093     
00094     z0 = sample*bq->gain + bq->z1*bq->a1 + bq->z2*bq->a2;
00095     y = z0 + bq->z1*bq->b1 + bq->z2*bq->b2;
00096 
00097     bq->z2 = bq->z1;
00098     bq->z1 = z0 >> 15;
00099 #if FIRST_ORDER_NOISE_SHAPING
00100     y += bq->residue; 
00101     bq->residue = y & 0x7FFF;
00102 #elif SECOND_ORDER_NOISE_SHAPING
00103     y += (2*bq->residue1 - bq->residue2);
00104     bq->residue2 = bq->residue1;
00105     bq->residue1 = y & 0x7FFF;
00106 #endif
00107     y >>= 15;
00108     return (int16_t) y;
00109 }
00110 /*- End of function --------------------------------------------------------*/
00111 
00112 #if defined(__cplusplus)
00113 }
00114 #endif
00115 
00116 #endif
00117 /*- End of file ------------------------------------------------------------*/