The NBC chimes of the National Broadcasting Company (NBC) radio network in the United States were the first ever audio trademark to be accepted by the U.S. Patent and Trademark Office. It consists of a succession of three distinct pitches: G3, E4, and C4 (middle C), sounded in that order, creating an arpeggiated C-major chord in the second inversion, within about two seconds time, and reverberating for another two or three seconds. The intervals of this progression are up a major 6th from G3 to E4 and down a major third from E4 to C4.

An elegant solution: the station break

The chimes were originally conceived to help solve a problem inherent in early network radio broadcasting, the vast majority of which was live, rather than pre-recorded. At the top of each hour, any individual broadcaster (on radio, TV or other broadcast band) must identify themselves by callsign and the name of the community where its broadcast license has been issued, in compliance with FCC regulations. For example: "This is KYW-TV, Philadelphia." Therefore it might seem efficient for a small radio network (three to seven stations, for instance) to accomplish this chore by having a single announcer "on the network", whose voice is transmitted to all the local stations, read the short list of local callsigns and corresponding communities for about ten seconds each hour, during an extended broadcast period. However, this practice becomes quite inefficient as a network grows, consuming valuable commercial airtimeNBC Network. Hence it was determined in early big-network radio days that this job, among others, had to be done locally, on a pre-determined cue from the network itself.