Switched-capacitor audio filter

In audio engineering there is often a requirement for a filter that either passes or blocks certain frequencies or frequency ranges. This requirement is met by the filter described in this article: the type of filter response required is available at the flick of a switch. The use of a special filter IC from National Semiconductor in conjunction with switched capacitors make the construction and alignment, eben for high-order configurations, straithforward. Although the filter is intended primarily for test and measurement, it may also be used for signal enhancement and noise suppression in short-wave receivers and for experimentation in electronic music.