Signal Filtering and System Control for Physiology

Abstract

Filters come in many forms from air filters and shock absorbers to digital filters. Using ideas from everyday filters like air filters, we can understand electronic filters. Electronic filters are familiarly used in audio systems as well as in all physiological measurement systems. During the recording of any signal, some undesirable signals termed “noise” are inevitably picked up. If the signal and noise are well separated in their frequency composition, we can use frequency filters that permit the passage of the desired signal while attenuating the other interfering signals. If the desired signal and the unwanted noise are not distinct, then we have to decide how best to reduce the noise while retaining as much as possible of the signal. This is the concept of an optimal filter. In many natural systems and artificial systems, where the output is affected by variations in the system properties or by disturbances added to the output, the desired response may be better achieved if the system is able to correct itself using some information about the actual output and its deviation from the desired output. Such systems are called feedback systems. The formal analysis of feedback system is useful in not only understanding the benefits of such feedback but also potential problems.

All stable processes we shall predict.All unstable processes we shall control.

– John von Neumann