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The Lombard, or voice reflex, effect results in speech with characteristics different from those of speech that is normally produced. This change of characteristics can be demonstrated as an effective way to combat noise interference during reception. It also demonstrates the advisability of control of the production of speech by the speaker himself, in addition to that offered by equipment, during audiological evaluations. Fifteen naive speakers read words and sentences while noise was being delivered to their headsets. There were five noise conditions. Their speech was recorded, with the noise being kept out of the recording channel, and then limited. Noise was then added to the recording in such a way as to produce a constant speech-to-noise ratio. The result was played to 200 American listeners. Results indicate that at a constant speech-to-noise ratio of reception speech produced by a talker with masking noise in his cars becomes more intelligible as the masking level rises to a given value. The change in intelligibility throughout the range investigated suggests an application to audiological testing as well as a device for use in voice communication.
Dreher et al. (Sun,) studied this question.