FFTToy -- A Fast Fourier Transformation filtering tool for practitioners and students

FFTToy was developed to enable practitioners to quickly examine and filter signals. In addition, with FFTToy you can simply generate artificial vectors comprised of sine waves and then use those vectors to test your FFT filter. The tool computes a multiplication in the Fourier domain using the FFT coefficient vector provided, which can also be directly pasted into the tool. By multiplying in the Fourier domain, virtually any shape of filter transformation curve can be achieved; hence, complicated combinations of band and low-pass filters can be built that don't distort the signal with phase delay.

Instructions

Begin your session entering n, to determine the length of your signal vector. In the above example, n is set to 13, meaning 2^13 = 8192 samples are being used; therefore, the above example uses are sample 0.8192 seconds long, since the sample rate is set to 10kHz.

Using the "Add sine" button you can add as many sine waves to your vector as you like using the settings above: amplitude, phase, and frequency. Note that negative amplitudes may be entered as well.

Press "Run FFT" to compute FFT coefficients, and the inverse FFT will be also computed to the right. Before the inverse is computed, a the values provided in the "Filtering by FFT product" box are multiplied in the FFT domain by the signal's FFT coefficients. A zero, for example, effectively removes the coefficient and hence removes a particular sine wave frequency component from the signal.

Hint: Use Microsoft Excel to edit and visualize vectors and FFT coefficients. You can copy and paste from and to FFTToy using the context menu (right mouse click into the text field).

Please email your comments to info@fastneuron.com.

Download FFTToy here.