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NAB Audio Cart Turns 40

The radio industry will pass a notable anniversary this fall, but one unlikely to be observed by too many people.

The radio industry will pass a notable anniversary this fall, but one unlikely to be observed by too many people. The NAB cart turns 40.

One of the many purposes of peer organizations such as the National Association of Broadcasters is to set standards in a given field to permit interchange and to unify business practices.

Some standards are forward-looking, such as the HD Radio specifications, in which we had a standard before the first HD station came on or receivers were built. Then we have backward-looking standards in which an industry development or practice is formalized.

An example of the latter is the NAB audio cartridge standard.

“Carts” – endless-loop 1/4-inch tape packages that could be played back without rewinding or rethreading – had been around the industry in various proprietary forms from the late 1950s.

The NAB standard, though, was published in October of 1964 – 40 years ago this fall.

This detailed standard dictated not only a cartridge’s physical dimensions and construction – carts came in multiple sizes – but also through performance requirements, the quality of the tape inside.

As in the story of Goldilocks, there were three cart sizes, AA, BB and CC, for increasing play lengths. Surprisingly, the NAB standard did not set any standard playing times; but cart vendors quickly focused on play time (and hence recue time) that most perfectly matched radio’s typical needs, such as the ubiquitous 40-second cart for 30-second commercials.

The standard further defined the playback machine capabilities, including track configuration; audio levels; flux record density; cue, logging and control tones (frequencies, levels, duration, etc.); flutter; phase differential in stereo; noise level; distortion; and response.

With the surety of this standard, a multitude of manufacturers entered the field, and cart machines appeared quickly, becoming de rigueur in virtually every radio station in the nation.

Today, with the conquest of computers and their cost-effective, transparent, voluminous hard-drive memory, the cart machine has been sent to the Dumpster.

A cottage industry continues to provide and repair machines and cart tapes for stalwarts who like the familiar convenience of having audio events segregated on a separate, reliable storage medium.