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Is there an easy way of drawing a noisy waveform in TikZ? I know you can draw a simple sinusoid by repeatedly using cos and sin for every half-period, but doing that for a noisy waveform seems like a massive undertaking and a very roundabout way of doing it.

I'm looking for something like this: Noisy waveform

It doesn't have to be that long, a fifth of the length is fine. I'm diagramming a noise reduction system and need to show a noisy waveform as the input to the diagram (whereas the rest of the diagram is simple rectangular boxes and text...).

Any ideas?

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2  
    
Thanks for that. I just discovered TikZ today and it's surprisingly powerful! –  jodles Nov 10 '13 at 21:30
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3 Answers

up vote 24 down vote accepted

You can use \draw plot for plotting functions. For the noise, you can use the rand function.

In general, plotting is more comfortable using the PGFPlots package, which builds on PGF/TikZ:

\documentclass{article}
\usepackage{pgfplots}
\begin{document}
    \begin{tikzpicture}[samples=200, domain=0:5*360]
        \begin{axis}[
            width=10cm, height=4cm,
            enlarge x limits=false,
            xtick=\empty,
            axis lines*=middle,
            hide y axis
        ]
        \addplot [no markers, smooth] {sin(x)+rand*2};
        \end{axis}
    \end{tikzpicture}
\end{document}
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This is a derived example from the »PGF/TikZ« user guide.

\documentclass{article}
\usepackage{tikz}

\begin{document}
  \begin{tikzpicture}[
    declare function={
      excitation(\t,\w) = sin(\t*\w);
      noise = rnd - 0.5;
      source(\t) = excitation(\t,20) + noise;
      filter(\t) = 1 - abs(sin(mod(\t, 50)));
      speech(\t) = 1 + source(\t)*filter(\t);
    }
  ]
    \draw[help lines] (0,1) -- (3,1);
    \draw[blue, thick, x=0.0085cm, y=1cm] (0,1) -- plot [domain=0:360, samples=144, smooth] (\x,{speech(\x)});
  \end{tikzpicture}
\end{document}

Customization is left to you.


enter image description here

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With PSTricks.

\documentclass[pstricks,border=12pt]{standalone}
\usepackage{pst-plot,pst-node}
\psset{plotpoints=200,linejoin=1}
\pstVerb{realtime srand}

\begin{document}
\psLoop{10}{%
\begin{pspicture}[showgrid=false](-4,-2)(4.5,2.5)
    \psaxes[labels=none,ticks=none,linecolor=gray]{->}(0,0)(-4,-2)(4,2)[$t$,0][$v$,90]
    \psplot[linecolor=red]{-3.8}{3.8}{x 5 mul RadtoDeg sin Rand 4 mul 1 sub mul 1.8 mul}
\end{pspicture}}
\end{document}

enter image description here

Attention

Note that Rand no longer produces a random real number between 0 and 0.5 inclusive. Its definition had been tacitly changed. Now it produces a random real number between 0 and 1 inclusive. It is not documented, nor announced, but it is still fun!

The code given above has not been updated yet so it will produce different output. I have no time to update it right now. Sorry for this inconvenience.

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A plot continuously moving from right to left would be even cooler. –  AlexG Nov 11 '13 at 7:51
    
@AlexG: Yes. I will see it later. –  I am who I say I am Nov 11 '13 at 8:22
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