Inverse FFT |
SIGVIEW Help Home |

Inverse FFT is a function which converts complex spectrum in a time-domain signal, i.e. the
function which reverts FFT result back in the origin signal. To apply this function, you need to
provide complex spectrum with real and imaginary components. Applying Inverse-FFT directly to
spectrum derivate like magnitude spectrum or power spectrum is not possible because important
phase information is not available anymore.

Inverse FFT in *SIGVIEW* is included in __Signal Calculator__ as a binary operator. It should be
applied to a real and imaginary spectrum part as shown in the screenshot below:

The result would look like this in the Control Window:

Real and imaginary spectrum parts can be obtained in *SIGVIEW *in two ways*:*

1.* *Calculate FFT twice for a signal and choose "__Real
part__" and "__Imaginary part__" in "__Show result
as__" field for these two spectrums respectively. For both spectrums, windowing and zero-expand
options should be turned off if you wish to get exactly the same signal after inverse FFT. After
calculating Inverse-FFT as shown above, resulting signal should be the same (up to the
calculation precision) as the origin signal. Please note that DC component of the origin signal will
also be lost, i.e. result of the Inverse-FFT will probably be translated for a constant offset on the
Y-axis from the origin signal. To avoid it, you can use __Remove DC offset__
function on the origin
signal before calculating its spectrum.

2. *SIGVIEW *distribution includes ready-to-use __custom
tool__ named "RealAndImagFFT" which will
automatically calculate real and imaginary FFT parts in two separate windows as described
above. You can use it to prepare data for the Inverse-FFT function. since this tool uses no zero-padding when calculating FFTs, we recommend using power-of-2 signal length for best
performance.