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Art and Science of Audio Book Production

Issued September 1995

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Original Masters


NLS specifications require the original master recordings of book titles intended for cassette duplication to have sound tracks of eighty-eight minutes duration. The two exceptions to this requirement are the final sound track of a book and a book that requires a sound track of fewer than eighty-eight minutes duration for the entire recorded text. Original masters are recorded on open-reel tapes at 3.75 inches per second with a half-track format. This is a practical combination for producing high quality original masters at reasonable cost for the following reasons:

Aberrations in tape oxide coating can cause signal breakup distortion, and dropout. A minor aberration that is quite audible in a quarter-track recording may not be audible in a half-track recording made on the same tape. The sound track made by a half-track record head is ninety-one percent wider than the sound track made by a quarter-track record head. It has more oxide recorded with the same signal than a quarter-track recording, so minor aberrations are less audible.

Signal to noise ratio (S/N) is a comparison of the level of the recorded signal to the level of noise inherent in the recording process, such as noise from tape oxide and record electronics. S/N is affected by soundtrack width and tape speed. As a rule, the wider the sound track and the faster the tape speed, the greater the S/N. As sound track width and tape speed decrease, so does S/N. A full-track recording has the best S/N when compared to half-track and quarter-track recordings, and quarter-track recordings have the lowest S/N.

The typical original master has two sound tracks, and two consecutive masters are needed to produce a four-track cassette.

Production Time versus Listening Time

A production team, which consists of a narrator, a monitor, and a reviewer, typically requires 5.5 staff hours to produce each hour of error-free recorded text. Each hour of finished sound track typically requires not less than 2 hours of studio time to produce; that requires 2 hours for a narrator and 2 hours for a monitor working together as a team for a total of 4 staff hours. The reviewer requires not less than 1.5 hours to review each hour of sound track because notes must be prepared to identify errors for correction by the narrator monitor team. The total time contributed by all three team members yields the 5.5 staff hours necessary to produce each hour of error-free recorded text. Thus, the typical two-track original master with just under 3 hours of listening time requires not less than 16.5 staff hours to produce.

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Posted on 2014-12-02