Can somebody point me out to some literature about how to calculate the impulse response or the step response from an experimental Frequency Response Function (epxerimental bode plot) measured at logarithmically spaced frequencies? I am looking into direct numerical methods, not passing by a model (i.e. not by identifying a model from the bode plot and then calculating the impulse or step response of the model). IFFT won't be of much help as experiment is done at logarithmically spaced frequencies.