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    <p>If you want to do something tailor-made, you could for example filter the low frequency components of the Fourier transform. </p> <p>Suppose we have the following signal:</p> <p><img src="https://i.stack.imgur.com/ZDVH9.png" alt="enter image description here"></p> <p>Then we calculate the FFT, and keep only the higher frequency components. Let's say we disregard the first 1.5% of the components. The resulting Plot of the original signal and the resulting oscillating one is: </p> <p><img src="https://i.stack.imgur.com/7HW0S.png" alt="enter image description here"></p> <p>HTH!</p> <p><strong>Edit 2</strong></p> <p>This is what you can expect from a hi-pass filter as described above, adding an exponential damping, instead of just disposing the low frequency components. </p> <p>Program in Mathematica (just in case): </p> <pre><code>centerOsc[x_] := Module[{list, n, fp, coef, s}, list = (Transpose@FinancialData[#, "Jan. 1, 2005"])[[2]] &amp;@x; n = Length@list; fp = Transpose[{N[Range[n]]/n, list}]; coef = FourierDST[list, 1]/Sqrt[n/2]; coef = Table[N[coef[[i]] (1 - E^(-i/6))], {i, 1, Length@coef}]; s = IntegerPart[Length@coef/100]; s = 1; {fp, {#, Sum[coef[[r]]*Sin[Pi r #], {r, s, n - 1}]} &amp; /@ (N[Range[n]]/ n)}]; l = {"GE", "GOOG", "IBM", "MSFT"} ;(*Real prices from*) GraphicsGrid@ Partition[ListLinePlot[centerOsc[#], Axes -&gt; False, Frame -&gt; True, PlotLabel -&gt; #, PlotRange -&gt; {{0.1, .9}, Full}, Epilog -&gt; Line[{{0, 0}, {1, 0}}]] &amp; /@ l, 2] </code></pre> <p><img src="https://i.stack.imgur.com/j2OTd.png" alt="enter image description here"></p> <p><strong>Edit 2</strong> </p> <p>Based on your last update, it seems that what you want can be achieved easier. Just see what you get by dividing reducing linearly the y axis by 50% and 80% (using <strong>your</strong> data, extracted from your plot): </p> <p><img src="https://i.stack.imgur.com/Oq53q.png" alt="enter image description here"></p> <p>and compare with your plot:</p> <p><img src="https://i.stack.imgur.com/5CDUT.png" alt="enter image description here"></p>
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