GB1432286A - Visual audio frequency comparator - Google Patents

Abstract

1432286 Tuning musical instruments MOTOROLA Inc 4 Sept 1974 [17 Sept 1973] 38711/74 Heading G5J [Also in Division G1] In a frequency comparator for use in tuning musical instruments, a display is provided which displays bars whose position and number indicate phase and frequency of the input signal and gating means supplies two signals alternately to the display. A cathode-ray tube 98 is operated in a split screen mode to display horizontal bars indicating a reference frequency on one half of the screen and a second frequency on the other half (Figs. 3-6, not shown). The horizontal oscillator (e.g. 15,750 Hz) produces a horizontal sweep in the normal way and is also used to drive a pair of parallel connected transistors 64<SP>1</SP>, 66 which pass a square-wave to the base of transistor 62 which thus short-circuits transistor 36 for half of each horizontal sweep. The square wave is also applied to transistors 74, 76 to invert it and passed to transistor 72 to short-circuit transistor 46 during the other half of the horizontal sweep. Consequently signals from one source corresponding to a first note pass through transistor 36 and are displayed on one half of the CRT screen and signals from a second source are displayed on the other half. One source provides vertical synchronization such that the reference signal is displayed as a stationary pattern. If required, the bars. may be vertical and a solid state display may be utilized.