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Cutoff frequency variable LPF, HPF, BPF, and BRF by FIR 160th-order filter.
Dependencies: UIT_ACM1602NI UITDSP_ADDA mbed UIT_AQM1602
WindowingDesign/WindowingDesign.cpp
- Committer:
- MikamiUitOpen
- Date:
- 2015-07-25
- Revision:
- 3:24b6aa1a19ba
- Parent:
- 0:ca94cfc90365
File content as of revision 3:24b6aa1a19ba:
//------------------------------------------------------------------------------ // Design of FIR filter of 4 type passbands using window method // // 2014/12/07, Copyright (c) 2014 MIKAMI, Naoki //------------------------------------------------------------------------------ #include "WindowingDesign.hpp" namespace Mikami { WindowingDesign::WindowingDesign(int order, float fs) : FS_(fs), PI_FS_(3.1415926536f/fs) { order_ = order; if ((order % 2) != 0) { fprintf(stderr, "order must be even."); return; } hm_ = new float[order/2+1]; wn_ = new float[order/2+1]; HammWindow(); } void WindowingDesign::Design(int order, Type pb, float fc1, float fc2, float hk[]) { if (pb == LPF) fC_ = fc1; if (pb == HPF) fC_ = 0.5f*FS_ - fc1; float w0 = PI_FS_*(fc1 + fc2); if ((pb == BPF) || (pb == BRF)) fC_ = 0.5f*fabs(fc2 - fc1); if (order != order_) { order_ = order_; if (hm_ != NULL) delete[] hm_; hm_ = new float[order/2+1]; if (wn_ != NULL) delete[] wn_; wn_ = new float[order/2+1]; HammWindow(); } // Calculate coefficients for LPF LpfCoefficients(); // If not LPF, transform coefficients if (pb != LPF) Transform(pb, w0); for (int k=0; k<=order/2; k++) hk[k] = hm_[order/2-k]; } // Calculation of coefficients for LPF void WindowingDesign::LpfCoefficients() { float w = 2.0f*PI_FS_*fC_; hm_[0] = 2.0f*fC_/FS_; for (int k=1; k<=order_/2; k++) hm_[k] = (sinf(k*w)/(PI_*k))*wn_[k]; } // Transform LPF to HPF, BPF, or BRF void WindowingDesign::Transform(Type pb, float w0) { if (pb == HPF) // To HPF for (int k=1; k<=order_/2; k+=2) hm_[k] = -hm_[k]; if (pb == BPF) // To BPF for (int k=0; k<=order_/2; k++) hm_[k] = 2.0f*cosf(w0*k)*hm_[k]; if (pb == BRF) // To BRF { hm_[0] = 1.0f - 2.0f*hm_[0]; for (int k=1; k<=order_/2; k++) hm_[k] = -2.0*cosf(w0*k)*hm_[k]; } } // Hamming window void WindowingDesign::HammWindow() { float pi2OvM = 2.0f*PI_/(float)(order_ + 1); for (int n=0; n<=order_/2; n++) wn_[n] = 0.54f + 0.46f*cosf(pi2OvM*n); } }