6. Real-time bandwidth

Each new DFT calculation corresponds to an update of the measured "spectrum". We could therefore imagine having a new spectrum for each apparent sampling period. However, this is not generally useful, and excludes the possibility of averaging.

In practice, the sequence currently being sampled is stored in a buffer, while the FFT processor calculates the spectrum of the previous sequence.

As long as the FFT calculation time (to which must be added measurement management time) remains less than the sampling time θ, no signal data is lost; successively processed slices are joined. The analyzer then works in real time (figure 33 ).

The sampling time θ is linked to the resolution-dispersion pair chosen: $\theta =\frac{N\text{/}2}{\text{Gamme de fréquences d’analyse }}$