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 
00027 /*! \page biquad_page Bi-quadratic filter sections
00028 \section biquad_page_sec_1 What does it do?
00029 ???.
00030 
00031 \section biquad_page_sec_2 How does it work?
00032 ???.
00033 */
00034 
00035 #if !defined(_SPANDSP_BIQUAD_H_)
00036 #define _SPANDSP_BIQUAD_H_
00037 
00038 typedef struct
00039 {
00040     int32_t gain;
00041     int32_t a1;
00042     int32_t a2;
00043     int32_t b1;
00044     int32_t b2;
00045 
00046     int32_t z1;
00047     int32_t z2;
00048 
00049 #if FIRST_ORDER_NOISE_SHAPING
00050     int32_t residue;
00051 #elif SECOND_ORDER_NOISE_SHAPING
00052     int32_t residue1;
00053     int32_t residue2;
00054 #endif
00055 } biquad2_state_t;
00056 
00057 #if defined(__cplusplus)
00058 extern "C"
00059 {
00060 #endif
00061 
00062 static __inline__ void biquad2_init(biquad2_state_t *bq,
00063                                     int32_t gain,
00064                                     int32_t a1,
00065                                     int32_t a2,
00066                                     int32_t b1,
00067                                     int32_t b2)
00068 {
00069     bq->gain = gain;
00070     bq->a1 = a1;
00071     bq->a2 = a2;
00072     bq->b1 = b1;
00073     bq->b2 = b2;
00074     
00075     bq->z1 = 0;
00076     bq->z2 = 0;    
00077 
00078 #if FIRST_ORDER_NOISE_SHAPING
00079     bq->residue = 0;
00080 #elif SECOND_ORDER_NOISE_SHAPING
00081     bq->residue1 = 0;
00082     bq->residue2 = 0;
00083 #endif
00084 }
00085 /*- End of function --------------------------------------------------------*/
00086 
00087 static __inline__ int16_t biquad2(biquad2_state_t *bq, int16_t sample)
00088 {
00089     int32_t y;
00090     int32_t z0;
00091     
00092     z0 = sample*bq->gain + bq->z1*bq->a1 + bq->z2*bq->a2;
00093     y = z0 + bq->z1*bq->b1 + bq->z2*bq->b2;
00094 
00095     bq->z2 = bq->z1;
00096     bq->z1 = z0 >> 15;
00097 #if FIRST_ORDER_NOISE_SHAPING
00098     y += bq->residue; 
00099     bq->residue = y & 0x7FFF;
00100 #elif SECOND_ORDER_NOISE_SHAPING
00101     y += (2*bq->residue1 - bq->residue2);
00102     bq->residue2 = bq->residue1;
00103     bq->residue1 = y & 0x7FFF;
00104 #endif
00105     y >>= 15;
00106     return (int16_t) y;
00107 }
00108 /*- End of function --------------------------------------------------------*/
00109 
00110 #if defined(__cplusplus)
00111 }
00112 #endif
00113 
00114 #endif
00115 /*- End of file ------------------------------------------------------------*/

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