File:Butterworth orders.png

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Original file(1,229 × 872 pixels, file size: 93 KB, MIME type: image/png)

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Description
English: Butterworth filter frequency response of several orders. Cutoff frequency is normalized to 1 rad/s. Gain is normalized to 0 dB in the passband.

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This plot was created with Gnuplot.
To convert the PostScript file to PNG:
  1. Open it in the GIMP (make sure you have ghostscript installed! - Windows instructions)
    • Enter 500 under Resolution (it doesn't say "DPI" but I think that's what it means)
    • Uncheck Try bounding box (since the bounding box cuts off the edge, unfortunately. You can try with the bounding box first.)
    • Enter large values for Width and Height
    • Check Color
    • Check Strong anti-aliasing for both graphics and text
  2. Crop off extra whitespace (Shift+C if you can't find it in the toolbox)
  3. Possibly need to rotate it: Click ImageTransformRotate 90 degrees clockwise
  4. FiltersBlurGaussian blur at 2.0 px (No need to blur if you use strong anti-aliasing during conversion. I see no significant difference between end results.)
  5. ImageScale Image...
    • Width and Height at 25%
    • Cubic interpolation
  6. You can view at normal size if you want by pressing 1, Ctrl+E
  7. Save as Butterworth orders.png
Date 20 July 2005 (upload date)
Source Own work
Author Omegatron
gnuplot source
InfoField
click to expand
 set samples 1001
 set terminal postscript enhanced landscape color solid lw 2 "Times-Roman" 20
 set output "butterworth_orders.ps"

 G(w,n) = 1 / (sqrt(1 + w**(2*n)))

 dB(x) = 20 * log10(abs(x))

 set grid

 # Set x axis to logarithmic scale
 set logscale x 10

 # Set range of x and y axes
 set xrange [0.01:100]
 set yrange [-100:10]

 # Create 10 x tick marks per decade
 set xtics 10

 set xlabel "Angular frequency (rad/s)"
 set ylabel "Gain (dB)"

 # Put legend in bottom left corner
 set key 0.1,-45

 # Plot five orders of the filter
 plot \
     dB(G(x,1)) title "1st order", \
     dB(G(x,2)) title "2nd order", \
     dB(G(x,3)) title "3rd order", \
     dB(G(x,4)) title "4th order", \
     dB(G(x,5)) title "5th order"

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Date/TimeThumbnailDimensionsUserComment
current00:07, 20 July 2005Thumbnail for version as of 00:07, 20 July 20051,229 × 872 (93 KB)Omegatron (talk | contribs)Butterworth filter of several orders.

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