BiquadGrEq.hpp

00001 //--------------------------------------------------------------
00002 //  グラフィックイコライザで使う 1D タイプの 2 次のフィルタ
00003 //  Biquad filter of 1D type for graphic equalizer
00004 //      このクラスでは，係数は実行中に書き換えられることを想定している
00005 //
00006 //      u[n] = x[n] + a1*u[n-1] + a2*u[n-2]
00007 //      y[n] = b0*u[n] + b1*u[n-1] + b2*u[n-2]
00008 //          x[n] :  input signal
00009 //          y[n] :  output signal
00010 //
00011 // 2017/03/28, Copyright (c) 2017 MIKAMI, Naoki
00012 //--------------------------------------------------------------
00013 
00014 #ifndef IIR_BIQUAD_GREQ_HPP
00015 #define IIR_BIQUAD_GREQ_HPP
00016 
00017 #include "mbed.h"
00018 
00019 // 2nd order IIR filter
00020 namespace Mikami
00021 {
00022     class BiquadGrEq
00023     {
00024     public:
00025         struct Coefs { float a1, a2, b0, b1, b2; };
00026 
00027         BiquadGrEq(const Coefs ck = (Coefs){0, 0, 0, 0, 0})
00028         {
00029             SetCoefficients(ck);
00030             Clear();
00031         }
00032         
00033         void SetCoefficients(const Coefs cf) { cf_ = cf; }
00034 
00035         float Execute(float xn)
00036         {
00037             float un = xn + cf_.a1*un1_ + cf_.a2*un2_;
00038             float yn = cf_.b0*un + cf_.b1*un1_ + cf_.b2*un2_;
00039         
00040             un2_ = un1_;
00041             un1_ = un;
00042 
00043             return yn;
00044         }
00045 
00046         void Clear() { un1_ = un2_ = 0; }
00047 
00048     private:
00049         Coefs cf_;
00050         float un1_, un2_;
00051 
00052         // disallow copy constructor
00053         BiquadGrEq(const BiquadGrEq&);
00054     };
00055 }
00056 #endif  // IIR_BIQUAD_GREQ_HPP