  This report proposes to discuss the Fourier domain analysis performances of a
RESPER probe. A uniform ADC, which is characterized by a sensible phase
inaccuracy depending on frequency, is connected to a Fast Fourier Transform
(FFT) processor, that is especially affected by a round-off amplitude noise
linked to both the FFT register length and samples number. If the register
length is equal to 32 bits, then the round-off noise is entirely negligible,
else, once bits are reduced to 16, a technique of compensation must occur. In
fact, oversampling can be employed within a short time window, reaching a
compromise between the needs of limiting the phase inaccuracy due to ADC and
not raising too much the number of averaged FFT values sufficient to bound the
round-off. Finally, the appendix presents an outline of somewhat lengthy
demonstrations needed to calculate the amplitude and especially phase
inaccuracies due to the round-off noise of FFT processors.
