Warning !

Soas is no longer maintained. You are strongly encouraged to switch to its successor, QSoas


(f) Filter (smooth using FFT).

This function allows the removal of regular and/or high frequency noise from the voltammograms.

The program allows you to change the cutoff (the highest relevant frequency, or the lowest relevant wavelength) and to see at the same time the raw (yellow) and FFTed (blue) data in the main box, and either the residue or the power spectra (of the raw and filtered data) in the lower box.

If you choose to monitor the residue (the difference between raw and ftted data), you should increase the filter size until the amplitude of the residue becomes greater than the noise (this means that you are over-filtering).

Alternatively, if the power spectrum is displayed, the cutoff can be directly selected using the mouse.

The screen capture below illustrates the effect of removing a band of intermediate frequencies on synthetic data set (y=sin(1/x))

The cutoff, the shape of the windowing function and the choice of viewing the power spectra instead of the residue are saved for the next time you use a FFT routine (f,d,D).

The option to let soas guess the filter size/shape is also saved. The next time you use the Fourier transform, the starting parameters of the filter will be set automatically. To disable this, type a again.

This command uses the public domain, real, fast Fourier transform from the NETLIB numerical library (http://www.netlib.org/fftpack/)

Warning !

Soas is no longer maintained. You are strongly encouraged to switch to its successor, QSoas
Christophe Leger 2009-02-24