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566
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1 function [h, w] = freqz(b,...) |
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904
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2 |
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3 # Compute the frequency response of a filter. |
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4 # |
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5 # [h,w] = resp(b) |
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6 # returns the complex frequency response h of the FIR filter with |
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7 # coefficients b. The response is evaluated at 512 angular frequencies |
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8 # between 0 and pi. w is a vector containing the 512 frequencies. |
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9 # |
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10 # [h,w] = resp(b,a) |
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11 # returns the complex frequency response of the rational IIR filter |
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12 # whose numerator has coefficients b and denominator coefficients a. |
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13 # |
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14 # [h,w] = resp(b,a,n) |
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15 # returns the response evaluated at n angular frequencies. For fastest |
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16 # computation n should factor into a small number of small primes. |
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566
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17 # |
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18 # [h,w] = freqz(b,a,n,"whole") |
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19 # evaluates the response at n frequencies between 0 and 2*pi. |
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20 |
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21 if (nargin == 1) |
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22 # Response of an FIR filter. |
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23 a = 1; |
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24 n = 512; |
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25 region = "half"; |
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26 elseif (nargin == 2) |
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27 # Response of an IIR filter |
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28 a = va_arg(); |
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29 n = 512; |
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30 region = "half"; |
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31 elseif (nargin == 3) |
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32 a = va_arg(); |
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33 n = va_arg(); |
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34 region = "half"; |
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35 elseif (nargin == 4) |
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36 a = va_arg(); |
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37 n = va_arg(); |
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38 region = va_arg(); |
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39 endif |
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40 |
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41 la = length(a); |
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42 a = reshape(a,1,la); |
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43 lb = length(b); |
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44 b = reshape(b,1,lb); |
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45 |
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46 k = max([la lb]); |
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47 |
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48 if( n >= k) |
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49 if (strcmp(region,"whole")) |
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50 h = fft(postpad(b,n)) ./ fft(postpad(a,n)); |
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51 w = 2*pi*[0:(n-1)]/n; |
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52 else |
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53 h = fft(postpad(b,2*n)) ./ fft(postpad(a,2*n)); |
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54 h = h(1:n); |
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55 w = pi*[0:(n-1)]/n; |
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56 endif |
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57 else |
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58 if (strcmp(region,"whole")) |
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59 w = 2*pi*[0:(n-1)]/n; |
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60 else |
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61 w = pi*[0:(n-1)]/n; |
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62 endif |
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63 h = polyval(postpad(b,k),exp(j*w)) ./ polyval(postpad(a,k),exp(j*w)); |
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64 endif |
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65 |
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66 endfunction |
