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 //   2017/03/28, Copyright (c) 2017 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         //      gDb : 利得（dB単位）
00024         BiquadGrEq::Coefs Execute(int band, float f0, float gDb, float qVal)
00025         {
00026             const float PI = 3.1415926536f;
00027             BiquadGrEq::Coefs coefs;
00028             
00029             float gSqrt = sqrtf(powf(10, gDb/20.0f));
00030             float w0 = 2.0f*PI*f0/FS_;
00031             
00032             if ( (band != 0) && (band != BANDS_-1) )    // ピーキングフィルタ
00033             {
00034                 float alpha = sinf(w0)/(2.0f*qVal);
00035                 float beta = 1.0f + alpha/gSqrt;
00036                 coefs.a1 = 2.0f*cosf(w0)/beta;
00037                 coefs.a2 = -(1.0f - alpha/gSqrt)/beta;
00038                 coefs.b0 = (1.0f + alpha*gSqrt)/beta;
00039                 coefs.b1 = -coefs.a1;
00040                 coefs.b2 = (1.0f - alpha*gSqrt)/beta;
00041             }
00042             else                                        // シェルビングフィルタ
00043             {                                           // Q は固定
00044                 w0 = (band == 0) ? w0*1.414f : w0/1.414f;
00045                 float alpha = sinf(w0)/sqrtf(2.0f); // Q = 1/sqrt(2)
00046                 float g_a = sqrtf(gSqrt);
00047                 float cosW0 = cosf(w0);
00048                 float gSqrtP1 = gSqrt+1.0f;
00049                 float gSqrtM1 = gSqrt-1.0f;
00050                 if (band == 0)      // ローシェルビング
00051                 {                   
00052                     float beta = gSqrtP1 + gSqrtM1*cosW0
00053                                + 2.0f*g_a*alpha;
00054                     coefs.a1 = 2.0f*(gSqrtM1 + gSqrtP1*cosW0)/beta;
00055                     coefs.a2 = -(gSqrtP1 + gSqrtM1*cosW0
00056                                - 2.0f*g_a*alpha)/beta;
00057                     coefs.b0 = gSqrt*(gSqrtP1 - gSqrtM1*cosW0
00058                                + 2.0f*g_a*alpha)/beta;
00059                     coefs.b1 = 2.0f*gSqrt*(gSqrtM1
00060                                - gSqrtP1*cosW0)/beta;
00061                     coefs.b2 = gSqrt*(gSqrtP1 - gSqrtM1*cosW0
00062                                - 2.0f*g_a*alpha)/beta;
00063                 }
00064                 else                // ハイシェルビング
00065                 {
00066                     float beta = gSqrtP1 - gSqrtM1*cosW0
00067                                + 2.0f*g_a*alpha;
00068                     coefs.a1 = -2.0f*(gSqrtM1 - gSqrtP1*cosW0)/beta;
00069                     coefs.a2 = -(gSqrtP1 - gSqrtM1*cosW0
00070                                - 2.0f*g_a*alpha)/beta;
00071                     coefs.b0 = gSqrt*(gSqrtP1 + gSqrtM1*cosW0
00072                                + 2.0f*g_a*alpha)/beta;
00073                     coefs.b1 = -2.0f*gSqrt*(gSqrtM1 + gSqrtP1*cosW0)/beta;
00074                     coefs.b2 = gSqrt*(gSqrtP1 + gSqrtM1*cosW0
00075                                - 2.0f*g_a*alpha)/beta;
00076                 }
00077             }
00078 
00079             return coefs;
00080         }
00081 
00082     private:
00083         const int BANDS_;
00084         const float FS_;
00085     };
00086 }
00087 #endif  // GRAPHIC_EQALIZER_PARAMETER_CALCULATOR_HPP