7413-A octave filter unit manufactured by Standard Telephones and Cables Ltd., London. A professional electronic test instrument designed to isolate and analyse specific frequency bands within an audio or signal range. The front panel features dual frequency range charts, rotary selector controls, connection terminals and indicator markings for use with associated measuring equipment such as a psophometer.
Octave filters of this type were used in telecommunications engineering, broadcast testing and acoustic measurement to separate signals into defined frequency bands for analysis of noise, transmission quality and circuit performance. The robust metal case reflects laboratory and field service use. 1950s to 1960s, during the expansion of telecommunications testing and audio engineering measurement systems.
