Image:Mains hum spectrum.png

[edit] Summary

A spectrum analysis of Mains hum, generated from an uncompressed file thanks to User:Omegatron, using Audacity. Important to note if comparing this to the other spectrum analyses on Colors of noise is that due to the signal having only a single major frequency component (so nearly all of the energy is concentrated in a small frequency band), the intensity scale range was increased by about 50% to show the full peak. Also, the frequency scale was adjusted to include 60Hz and its surrounding frequencies.

[edit] Instructions

Gather spectrum analysis data with Audacity. Run gnuplot on this data with the following script:

set terminal png transparent font "/usr/share/fonts/truetype/ttf-bitstream-vera/Vera.ttf" size 800,600 enhanced
set output "mains_hum_spectrum.png"

# this seems to fix the trailers on the TTF font for the x-label
set bmargin 4

# enable grid
set grid
set grid mxtics

# set up x-axis
set logscale x 10
set xrange [20:22000]
set xlabel "Frequency (Hz)"
set xtics border nomirror

# set up y-axis
set yrange [-40:30]
set ylabel "Intensity (dB)"
set ytics border nomirror

# again to deal with bad bboxes on the TTF...
set key height 1 box

# plot the output from Audacity
plot "mains_hum.txt" title "Mains Hum" with filledcurves x1 3

[edit] Licensing

This image has been (or is hereby) released into the public domain by its author, Ktims at the English Wikipedia project. This applies worldwide. In case this is not legally possible: Ktims grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.

• Mains hum