Bela
Real-time, ultra-low-latency audio and sensor processing system for BeagleBone Black
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IirFilter.h
1 /*
2  * IirFilter.h
3  *
4  * Created on: 17 Sep 2015
5  * Author: giulio
6  */
7 
8 #ifndef IIRFILTER_H_
9 #define IIRFILTER_H_
10 
11 #define IIR_FILTER_STAGE_COEFFICIENTS (5)
12 #define IIR_FILTER_STAGE_STATES (IIR_FILTER_STAGE_COEFFICIENTS - 1)
13 
14 class IirFilterStage{ //TODO : to save (some) memory we should only store the coefficients pointers here,
15  //so that IirFilter can share them among multiple stages if needbe)
16 private:
17  double coefficients[IIR_FILTER_STAGE_COEFFICIENTS]; // these are b0,b1,b2,a1,a2
18  double states[IIR_FILTER_STAGE_STATES]; // these are xprev, xprevprev, yprev, yprevprev
19 public:
21  void setCoefficients(double* newCoefficients);
22  void setStates(double* newStates);
23  // this is not meant to be efficient, just of practical use!
24  double process(double in){
25  process(&in, 1);
26  return in;
27  }
28 
29  void process(double* inout, int length){
30  // make variables explicit. A smart compiler will optimize these out, right?
31  double b0=coefficients[0];
32  double b1=coefficients[1];
33  double b2=coefficients[2];
34  double a1=coefficients[3];
35  double a2=coefficients[4];
36  double x1 = states[0];
37  double x2= states[1];
38  double y1 = states[2];
39  double y2 = states[3];
40  for(int n = 0; n < length; n++){
41  double x0 = inout[n];
42  double y = x0 * b0 + x1 * b1 + x2 * b2 +
43  - y1 * a1 - y2 * a2;
44  inout[n] = y;
45  x2 = x1;
46  x1 = x0;
47  y2 = y1;
48  y1 = y;
49  }
50  states[0] = x1;
51  states[1] = x2;
52  states[2] = y1;
53  states[3] = y2;
54  }
55 };
56 
57 class IirFilter{
58 private:
59  IirFilterStage** stages = 0;
60  int numberOfStages = 0;
61  void dealloc();
62 public:
63  IirFilter();
64  IirFilter(int newNumberOfStages);
65  IirFilter(int newNumberOfStages, double *newCoefficients);
66  void setCoefficients(double* newCoefficients);
67  void setCoefficients(double* newCoefficients, unsigned int stage);
68  void setStates(double* newStates);
69  void setStates(double* newStates, unsigned int stage);
70  void setNumberOfStages(int newNumberOfStages);
71 // double process(double in);
72 // inline void process(double* inout, int length);
73 // inline void process(double* in, double* out, int length);
74  double process(double in){
75  process(&in, 1);
76  return in;
77  };
78  void process(double* inout, int length){
79  for(int n = 0; n < numberOfStages && n < 8/* TODO: this "8" compensates for a memory corruption somewhere on the BBB*/; n++){
80  stages[n]->process(inout, length);
81  }
82  }
83 };
84 
85 
86 //void IirFilter::process(double* in, double* out, int length);
87 
88 #endif /* IIRFILTER_H_ */
Definition: IirFilter.h:57
Definition: IirFilter.h:14