Dual FFT

Under dual FFT (short for dual Fast Fourier Transformation , English for "dual Fast Fourier Transform") refers to the determination of the frequency response by comparing two spectra . For this purpose, the excitation and the result signal are digitized, then the spectrum of both signals is calculated using the Fast Fourier Transformation (FFT). Now the values ​​at the individual frequencies are divided by one another. If the route includes a transit time , the reference signal must be delayed accordingly before the FFT. The result then shows the spectrum of the impulse response of the system, with the phase shifted according to the delay of the reference signal. If required, this can be calculated using the inverse FFT from the result of the dual FFT. In this case, the reference signal must not be delayed before the calculation, otherwise the temporal position of the impulse response must be corrected accordingly.