求达人帮我分析下FIR滤波器的设计

wxm27811

题目是这个样子的：
设计FIR滤波器（低通，四种窗函数， fs＝1200Hz, 截止频率300Hz,
阶数自选, 画频率特性并分析比较)。

最好的话，能够帮我解决一下，实在是隔行如隔山~一点不通啊。。。
多谢~~

wxm27811

谁知道阻带频率和题目中的关系？

wxm27811

这个是我用工具箱做的。希望对后来人有帮助。

1. clear;
   
2. Fs = 1200;  % Sampling Frequency
   
3. 
   
4. N    = 19;       % Order
   
5. Fc   = 300;      % Cutoff Frequency
   
6. flag = 'scale';  % Sampling Flag
   
7. Beta = 0.5;      % Window Parameter
   
8. %% 凯撒窗  %%
   
9. % Create the window vector for the design algorithm.
   
10. win = kaiser(N+1, Beta);
    
11. 
    
12. % Calculate the coefficients using the FIR1 function.
    
13. b  = fir1(N, Fc/(Fs/2), 'low', win, flag)
    
14. [h,f] = freqz(b,1,2048,1200);
    
15. figure;
    
16. plot(f,20*log10((abs(h))))
    
17. title('凯撒窗')
    
18. 
    
19. %% 矩形窗  %%
    
20. % Create the window vector for the design algorithm.
    
21. win = rectwin(N+1);
    
22. 
    
23. % Calculate the coefficients using the FIR1 function.
    
24. b  = fir1(N, Fc/(Fs/2), 'low', win, flag)
    
25. [h,f] = freqz(b,1,2048,1200);
    
26. figure;
    
27. plot(f,20*log10((abs(h))))
    
28. title('矩形窗')
    
29. 
    
30. %% 海明窗  %%
    
31. % Create the window vector for the design algorithm.
    
32. win = hamming(N+1);
    
33. 
    
34. % Calculate the coefficients using the FIR1 function.
    
35. b  = fir1(N, Fc/(Fs/2), 'low', win, flag)
    
36. [h,f] = freqz(b,1,2048,1200);
    
37. figure;
    
38. plot(f,20*log10((abs(h))))
    
39. title('海明窗')
    
40. 
    
41. %% 汉宁窗  %%
    
42. % Create the window vector for the design algorithm.
    
43. win = hann(N+1);
    
44. 
    
45. % Calculate the coefficients using the FIR1 function.
    
46. b  = fir1(N, Fc/(Fs/2), 'low', win, flag)
    
47. [h,f] = freqz(b,1,2048,1200);
    
48. figure;
    
49. plot(f,20*log10((abs(h))))
    
50. title('汉宁窗')
    
51. 
    
52. %% 布莱克曼窗  %%
    
53. % Create the window vector for the design algorithm.
    
54. win = blackman(N+1);
    
55. 
    
56. % Calculate the coefficients using the FIR1 function.
    
57. b  = fir1(N, Fc/(Fs/2), 'low', win, flag)
    
58. [h,f] = freqz(b,1,2048,1200);
    
59. figure;
    
60. plot(f,20*log10((abs(h))))
    
61. title('布莱克曼窗')

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