Speech and music can convey information only as far as their dynamic range exceeds the masking-threshold due to environmental noise. The dynamic range, available for transmission above the threshold, however, is restricted by annoying loudness, self-masking, and requirements concerning conservation of hearing. A matched combination of compression and reshaping of the spectral power distribution of the speech and music program enables a concentration of information within the restricted available dynamic range and consequently effects optimum transmission conditions in noisy environments. As an example of a system according to this principle, reference is made to the Environmental Radio System, designed for 3-channel simultaneous F.M. wireless transmission for high-quality music distribution and speech communication, to be used for ambulant personnel in factories with high acoustic noise level and high interfering electric and magnetic fields.
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