ddsp.filter.biquad source code

1 /**
2 * Copyright 2017 Cut Through Recordings
3 * License: MIT License
4 * Author(s): Ethan Reker
5 */
6 module ddsp.filter.biquad;
7 
8 import ddsp.effect.effect;
9 
10 const float pi = 3.14159265;
11 
12 enum FilterType
13 {
14     lowpass,
15     highpass,
16     bandpass,
17     allpass,
18     peak,
19     lowshelf,
20     highshelf,
21 }
22 
23 /**
24 This class implements a generic biquad filter. Should be inherited by all filters.
25 */
26 class BiQuad(T) : AudioEffect!T
27 {
28     public:
29 
30         this() nothrow @nogc
31         {
32 
33         }
34 
35         void initialize(T a0,
36                         T a1,
37                         T a2,
38                         T b1,
39                         T b2,
40                         T c0 = 1,
41                         T d0 = 0)  nothrow @nogc
42         {
43            _a0 = a0;
44            _a1 = a1;
45            _a2 = a2;
46            _b1 = b1;
47            _b2 = b2;
48            _c0 = c0;
49            _d0 = d0;
50         }
51         
52         void setFrequency(float frequency) nothrow @nogc
53         {
54             if(_frequency != frequency)
55             {
56                 _frequency = frequency;
57                 calcCoefficients();
58             }
59         }
60     
61         override void setSampleRate(float sampleRate) nothrow @nogc
62         {
63             _sampleRate = sampleRate;
64             calcCoefficients();
65             reset();
66         }
67 
68         override T getNextSample(const T input)  nothrow @nogc
69         {
70             _w = input - _b1 * _w1 - _b2 * _w2;
71             _yn = (_a0 * _w + _a1 *_w1 + _a2 * _w2) * _c0 + (input * _d0);
72 
73             _w2 = _w1;
74             _w1 = _w;
75 
76             return _yn;
77         }
78 
79         override void reset()
80         {
81             _w = 0;
82             _w1 = 0;
83             _w2 = 0;
84 
85             _yn = 0;
86         }
87 
88         abstract void calcCoefficients() nothrow @nogc;
89 
90     protected:
91 
92         //Delay samples
93         float _w = 0;
94         float _w1 = 0;
95         float _w2 = 0;
96         float _yn = 0;
97 
98         //Biquad Coeffecients
99         T _a0=0, _a1=0, _a2=0;
100         T _b1=0, _b2=0;
101         T _c0=1, _d0=0;
102 
103         float _sampleRate;
104         float _qFactor;
105         float _frequency;
106 }