00001 /* 00002 $Id: BiquadUG.h 3282 2005-05-22 07:35:24Z leighsmith $ 00003 00004 Defined In: The MusicKit 00005 Description: 00006 BiquadUG.h - Two-pole, two-zero, filter section, with gain. 00007 00008 The BiquadUG unit-generator implements a two-pole, two-zero filter 00009 section in direct form. The output space can only be y DSP memory. 00010 Therefore, only two leaf classes exist, BiquadUGx and BiquadUGy, 00011 corresponding to the two possible input spaces. 00012 00013 The biquad transfer function is 00014 00015 -1 -2 00016 1 + b1 * z + b2 * z 00017 H(z) = g * ------------------------- 00018 -1 -2 00019 1 + a1 * z + a2 * z 00020 00021 The biquad difference equation which implements H(z) is 00022 00023 v(n) = g * x(n) - a1 * v(n-1) - a2 * v(n-2); 00024 y(n) = v(n) + b1 * v(n-1) + b2 * v(n-2); 00025 00026 where n denotes the current sample time, x(n) is the input signal at 00027 time n, y(n) is the output signal, and v(n) is an intermediate signal 00028 between the poles section and the zeros section. This is the 00029 so-called direct-form digital filter structure, which follows 00030 immediately from the transfer function definiteion. In the DSP, which 00031 uses fixed-point arithmetic, the so-called "transposed direct form" is 00032 used instead to avoid the possibility of internal overflow of v(n). 00033 However, the transfer function is equivalent. See Digital Signal 00034 Processing by A.V. Oppenheim and R.W. Schafer (Prentice-Hall, 1975, 00035 p. 155) for further discussion. 00036 00037 You instantiate a subclass of the form 00038 BiquadUG<a><b>, where <a> = space of output and <b> = space of input. 00039 00040 Original Author: David A. Jaffe 00041 00042 Copyright (c) 1988-1992, NeXT Computer, Inc. 00043 Portions Copyright (c) 1994 NeXT Computer, Inc. and reproduced under license from NeXT 00044 Portions Copyright (c) 1994 Stanford University. 00045 Portions Copyright (c) 1999-2001, The MusicKit Project. 00046 */ 00087 #ifndef __MK_BiquadUG_H___ 00088 #define __MK_BiquadUG_H___ 00089 00090 #import <MusicKit/MKUnitGenerator.h> 00091 00092 @interface BiquadUG : MKUnitGenerator 00093 { 00094 } 00095 00096 00104 - setInput:(id)aPatchPoint; 00105 /* Sets filter input. */ 00106 00107 00115 - setOutput:(id)aPatchPoint; 00116 /* Sets filter output. */ 00117 00118 00125 - clear; 00126 /* Clear internal filter state. */ 00127 00136 - setFirstDelayedSample:(double)d1; 00137 00146 - setSecondDelayedSample:(double)d2; 00147 00148 /* The following four methods set the corresponding coefficients. See 00149 * discussion above. 00150 */ 00151 00159 - setA1:(double)a1; 00160 00168 - setA2:(double)a2; 00169 00177 - setB1:(double)b1; 00178 00186 - setB2:(double)b2; 00187 00188 00196 - setGain:(double)g; 00197 /* Sets gain of filter. */ 00198 00207 +(BOOL)shouldOptimize:(unsigned) arg; 00208 /* Specifies that all arguments are to be optimized if possible except the 00209 * filter state. */ 00210 00211 /* The following provide more convenient ways to talk to the filters. */ 00212 00224 - setComplexPolesRadius:(double)r angle:(double)t; 00225 /* Sets the coefficients such as to provide the specified pole radius and 00226 * angle. The angle is in radians. */ 00227 00228 00240 - setComplexZerosRadius:(double)r angle:(double)t; 00241 /* Sets the coefficients such as to provide the specified zero radius and 00242 * angle. The angle is in radians. */ 00243 00244 00256 - setComplexPolesFrequency:(double)f bandwidth:(double)b; 00257 /* Sets the coefficients such as to place the poles at the specified freq 00258 * and bandwidth. */ 00259 00260 00272 - setComplexZerosFrequency:(double)f bandwidth:(double)b; 00273 /* Sets the coefficients such as to place the zeros at the specified freq 00274 * and bandwidth. */ 00275 00286 - setComplexPolesFrequency:(double)f t60:(double)t60; 00287 00288 @end 00289 00290 #endif
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