Guralp-systems Strong Motion Manuale Utente Scaricare il pdf (Pagina 14)

Strong Motion User Guide

is a set of four cascaded first-order IIR filters. Its roll off is

comparitively more shallow and begins at a lower frequency.

The phase shift observed in illustration 2 is actually a linear

phase shift introduced by a pure time delay. The FIR filter used

has a completely flat phase response, but is acausal. A pure

time delay must be used so that the filter can be realised. This

simply means that the output sample y(t) does not correspond

to the input sample u(t) but instead to the sample u(t-n).

14 Issue F

Illustration 2: Bode plot of normal 200Hz to 20Hz pre-decimation

FIR filter.

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Guralp-systems Strong Motion Manuale Utente Pagina 14