The NBC chimes are a sequence of three tones played on National Broadcasting Company (NBC) broadcasts. Originally developed in 1927 as seven notes, they were standardized to the current three-note version by the early 1930s, and possibly as early as 1929. The chimes were originally employed as an audible programming cue, used to alert network control engineers and the announcers at NBC's radio network affiliates. They soon became associated with NBC programming in general, and are an early example of an "interval signal" used to help establish a broadcaster's identity with its audience.
In 1950 the NBC chimes became the first "purely audio" service mark granted by the U.S. Patent and Trademark Office. They continue to be used as an audio signature by the NBC TV network and its affiliates, and also on the NBC Sports Radio network and at the opening of the hourly NBC News Radio broadcasts.