Principles of digital filtering

The digital computer is a versatile tool that may be used to filter seismic traces. Conventional filtering is performed by means of analog-type electronic networks, whose behavior is ordinarily studied in the frequency domain. Digital filtering, on the other hand, is more fruitfully treated in the time domain. A digital filter is represented by a sequence of numbers called weighting coefficients. The output of a digital filter is obtained by convolving the digitized input trace with the filter's weighting coefficients. The mechanics of digital filtering in the time domain are described with the aid of discrete z-transform theory. These ideas are then related to the more familiar interpretation of filter behavior in the frequency domain. An important criterion for the classification of filters is the notion of "minimum phase-lag". This paper ends with a new and simple presentation of this concept.