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Cutoff frequency variable LPF and HPF by 160th-order FIR filter designed by window method usin Hamming window for ST Nucleo F401RE.
Dependencies: UIT_ACM1602NI UIT_ADDA mbed
Diff: WindowingDesignLpfHpf/WindowingDesignLH.cpp
- Revision:
- 0:ea9a0c65a7dd
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/WindowingDesignLpfHpf/WindowingDesignLH.cpp Mon Nov 10 03:03:18 2014 +0000 @@ -0,0 +1,92 @@ +//------------------------------------------------------------------------------ +// Design of FIR filter of LPF and HPF using window method +// +// 2014/11/09, Copyright (c) 2014 MIKAMI, Naoki +//------------------------------------------------------------------------------ + +#include "WindowingDesignLH.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 fc, + float hk[]) + { + if (pb == LPF) fC_ = fc; + if (pb == HPF) fC_ = 0.5f*FS_ - fc; + + 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 HPF, transform coefficients + if (pb != LPF) ToHpf(); + + for (int k=0; k<=order/2; k++) + hk[k] = hm_[order/2-k]; + + // For compensation of gain + float sum = hk[order_/2]; + if (pb == LPF) + for (int k=0; k<order_/2; k++) + sum = sum + 2.0f*hk[k]; + if (pb == HPF) + { + float sign = -1.0; + for (int k=order_/2-1; k>=0; k--) + { + sum = sum + sign*2.0f*hk[k]; + sign = -sign; + } + } + for (int k=0; k<=order_/2; k++) + hk[k] = hk[k]/sum; + } + + // 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 + void WindowingDesign::ToHpf() + { + for (int k=1; k<=order_/2; k+=2) + hm_[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); + } +} +