SMPTE EG 14-1999

This guideline provides measurement methods and recommended levels for background noise sound pressure levels in dubbing stages. The purpose of adding intentional background noise to dubbing stages is to match the environment of the dubbing stage to the average theater environment, for best translation of the program material from dubbing stage to theater.
The practice is intended for application when the background noise is essentially a steady state sound, without strong time-varying components.
The background noise may be produced by air-handling systems, by adding noise to the monitoring system, or by a combination of these. An advantage to adding noise electronically is the ability to switch off the noise, for reproduction of the fullest possible dynamic range of the program material, exceeding that of most theaters, so long as the air-handling system note of the dubbing stage is quieter than most theaters.