GrEqParamsCalculator.hpp

00001 //------------------------------------------------------------------------------
00002 //  Parameters calculator class of buquad unit for graphic equalizer
00003 //  グラフィックイコライザで使う biquad フィルタの係数を計算するクラス
00004 //
00005 //   2016/05/09, Copyright (c) 2016 MIKAMI, Naoki
00006 //------------------------------------------------------------------------------
00007 
00008 #ifndef GRAPHIC_EQALIZER_PARAMETER_CALCULATOR_HPP
00009 #define GRAPHIC_EQALIZER_PARAMETER_CALCULATOR_HPP
00010 
00011 #include "mbed.h"
00012 #include "BiquadGrEq.hpp"
00013 
00014 namespace Mikami
00015 {
00016     class GrEqParams
00017     {
00018     public:
00019         // Constructor
00020         GrEqParams(int bands, float fs) : BANDS_(bands), FS_(fs) {}
00021 
00022         // 係数を計算する
00023         BiquadGrEq::Coefs Execute(int band, float f0, float gDb, float qVal)
00024         {
00025             const float PI = 3.1415926536f;
00026             BiquadGrEq::Coefs coefs;
00027             
00028             float gSqrt = sqrtf(powf(10, gDb/20.0f));
00029             float w0 = 2.0f*PI*f0/FS_;
00030             
00031             if ( (band != 0) && (band != BANDS_-1) )
00032             {
00033                 float alpha = sinf(w0)/(2.0f*qVal);
00034                 float a0 = 1.0f + alpha/gSqrt;
00035                 coefs.a1 = 2.0f*cosf(w0)/a0;
00036                 coefs.a2 = -(1.0f - alpha/gSqrt)/a0;
00037                 coefs.b0 = (1.0f + alpha*gSqrt)/a0;
00038                 coefs.b1 = -coefs.a1;
00039                 coefs.b2 = (1.0f - alpha*gSqrt)/a0;
00040             }
00041             else
00042             {
00043                 w0 = (band == 0) ? w0*1.414f : w0/1.414f;
00044                 float alpha = sinf(w0)/sqrtf(2.0f); // Q = 1/sqrt(2)
00045                 float g_a = sqrtf(gSqrt);
00046                 float cosW0 = cosf(w0);
00047                 float gSqrtP1 = gSqrt+1.0f;
00048                 float gSqrtM1 = gSqrt-1.0f;
00049                 if (band == 0)
00050                 {                   
00051                     float a0 = gSqrtP1 + gSqrtM1*cosW0
00052                                + 2.0f*g_a*alpha;
00053                     coefs.a1 = 2.0f*(gSqrtM1 + gSqrtP1*cosW0)/a0;
00054                     coefs.a2 = -(gSqrtP1 + gSqrtM1*cosW0
00055                                - 2.0f*g_a*alpha)/a0;
00056                     coefs.b0 = gSqrt*(gSqrtP1 - gSqrtM1*cosW0
00057                                + 2.0f*g_a*alpha)/a0;
00058                     coefs.b1 = 2.0f*gSqrt*(gSqrtM1
00059                                - gSqrtP1*cosW0)/a0;
00060                     coefs.b2 = gSqrt*(gSqrtP1 - gSqrtM1*cosW0
00061                                - 2.0f*g_a*alpha)/a0;
00062                 }
00063                 else
00064                 {
00065                     float a0 = gSqrtP1 - gSqrtM1*cosW0
00066                                + 2.0f*g_a*alpha;
00067                     coefs.a1 = -2.0f*(gSqrtM1 - gSqrtP1*cosW0)/a0;
00068                     coefs.a2 = -(gSqrtP1 - gSqrtM1*cosW0
00069                                - 2.0f*g_a*alpha)/a0;
00070                     coefs.b0 = gSqrt*(gSqrtP1 + gSqrtM1*cosW0
00071                                + 2.0f*g_a*alpha)/a0;
00072                     coefs.b1 = -2.0f*gSqrt*(gSqrtM1 + gSqrtP1*cosW0)/a0;
00073                     coefs.b2 = gSqrt*(gSqrtP1 + gSqrtM1*cosW0
00074                                - 2.0f*g_a*alpha)/a0;
00075                 }
00076             }
00077 
00078             return coefs;
00079         }
00080 
00081     private:
00082         const int BANDS_;
00083         const float FS_;
00084     };
00085 }
00086 #endif  // GRAPHIC_EQALIZER_PARAMETER_CALCULATOR_HPP