The digital anti-alias filter

Abstract

High performance seismic recording systems that make use of oversampling and decimation techniques reduce the requirements on the analog anti-alias filters because most of the filtering is performed in the digital domain (cf. Fig. 6.16). The quantization noise level of such systems decreases within the passband of interest with the ratio of the original Nyquist frequency to the final Nyquist frequency (oversampling ratio). On the other hand, it is desirable to keep the usable frequency range for the signal (passband of the anti-alias filter) as wide as possible. For this reason, digital anti-alias filters with very steep transition bands are needed to obtain the best resolution for a given frequency band of interest. The filter should also leave a band-limited signal which falls completely within the passband as unaffected as possible, causing neither amplitude nor phase distortions.