不韋 呂
Output the audio signal with filtering by IIR filter in the *.wav file on the SD card using onboard CODEC. SD カードの *.wav ファイルのオーディオ信号を遮断周波数可変の IIR フィルタを通して，ボードに搭載されているCODEC で出力する．
Dependencies: BSP_DISCO_F746NG F746_GUI LCD_DISCO_F746NG SDFileSystem_Warning_Fixed TS_DISCO_F746NG mbed FrequencyResponseDrawer F746_SAI_IO Array_Matrix
Diff: MyClasses_Functions/BilinearDesignLH.cpp
- Revision:
- 0:04b43b777fae
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/MyClasses_Functions/BilinearDesignLH.cpp Tue Apr 19 09:46:11 2016 +0000
@@ -0,0 +1,76 @@
+//------------------------------------------------------------------------------
+// Design of Butterworth LPF and HPF using bilinear transform
+//
+// 2016/03/31, Copyright (c) 2016 MIKAMI, Naoki
+//------------------------------------------------------------------------------
+
+#include "BilinearDesignLH.hpp"
+
+namespace Mikami
+{
+ // Execute design
+ // input
+ // fc: Cutoff frequency
+ // pb: Passband (LPF or HPF)
+ // output
+ // c : Coefficients for cascade structure
+ // g : Gain factor for cascade structure
+ void BilinearDesign::Execute(float fc, Type pb, Coefs c[], float& g)
+ {
+ Butterworth();
+ Bilinear(fc);
+ ToCascade(pb);
+ GetGain(pb);
+ GetCoefs(c, g);
+ }
+
+ // Get poles for Butterworth characteristics
+ void BilinearDesign::Butterworth()
+ {
+ float pi_2order = PI_/(2.0f*ORDER_);
+ for (int j=0; j<ORDER_/2; j++) // Pole with imaginary part >= 0
+ {
+ float theta = (2.0f*j + 1.0f)*pi_2order;
+ sP_[j] = Complex(-cosf(theta), sinf(theta));
+ }
+ }
+
+ // Bilinear transform
+ // fc: Cutoff frequency
+ void BilinearDesign::Bilinear(float fc)
+ {
+ float wc = tanf(fc*PI_FS_);
+ for (int k=0; k<ORDER_/2; k++)
+ zP_[k] = (1.0f + wc*sP_[k])/(1.0f - wc*sP_[k]);
+ }
+
+ // Convert to coefficients for cascade structure
+ void BilinearDesign::ToCascade(Type pb)
+ {
+ for (int j=0; j<ORDER_/2; j++)
+ {
+ ck_[j].a1 = 2.0f*real(zP_[j]); // a1m
+ ck_[j].a2 = -norm(zP_[j]); // a2m
+ ck_[j].b1 = (pb == LPF) ? 2.0f : -2.0f; // b1m
+ ck_[j].b2 = 1.0f; // b2m
+ }
+ }
+
+ // Calculate gain factor
+ void BilinearDesign::GetGain(Type pb)
+ {
+ float u = (pb == LPF) ? 1.0f : -1.0f;
+ float g0 = 1.0f;
+ for (int k=0; k<ORDER_/2; k++)
+ g0 = g0*(1.0f - (ck_[k].a1 + ck_[k].a2*u)*u)/
+ (1.0f + (ck_[k].b1 + ck_[k].b2*u)*u);
+ gain_ = g0;
+ }
+
+ // Get coefficients
+ void BilinearDesign::GetCoefs(Coefs c[], float& gain)
+ {
+ for (int k=0; k<ORDER_/2; k++) c[k] = ck_[k];
+ gain = gain_;
+ }
+}