matlab濾波器設計

1. 選定濾波器與其規格，以下隨意兩項會決定另一項的數值
• Filter order
• Transition width
• Peak passband/stopband ripple
2. 使用fvtool function檢查濾波器圖形
3. 檢查Group delay
4. shift訊號或是選用zero-phase filter來消除Group delay

FIR vs IIR

• IIR相比FIR有較少的濾波器階數，資源消耗較少
• IIR的group delay是非線性的

範例：

%Bandpass filter with Passband [50 400], Stopband frequency [45 405], Stopband attenuation [60], Passband Ripple [1000]. 

BPfilt = designfilt('bandpassfir', 'StopbandFrequency1', 45, 'PassbandFrequency1', 50, 'PassbandFrequency2', 400, 'StopbandFrequency2', 405, 'StopbandAttenuation1', 60, 'PassbandRipple', 1, 'StopbandAttenuation2', 60, 'SampleRate', 1000);

fvtool(BPfilt) %檢查濾波器波型

grpdelay(BPfilt) %檢查Group delay

D = mean(grpdelay(BPfilt));% Shift data去補償Group delay的影響 

y = filter(BPfilt,[YourData; zeros(D,1)]);  % 增加D zeros

y = y(D+1:end); 

相關文章：

• https://www.mathworks.com/help/signal/ref/designfilt.html
• https://www.mathworks.com/help/signal/ug/practical-introduction-to-digital-filter-design.html
• https://www.mathworks.com/help/signal/ug/practical-introduction-to-digital-filtering.html
• https://www.mathworks.com/help/signal/ref/filtfilt.html