A four-stage FM broadcast audio peak limiter

The design of a peak limiter processor for FM broadcast audio is described. The limiter has four gain control stages. The basic peak limiting function is performed in the first and second stages by a slow-attach-slow-release stage followed by a fast-attack-fast-release stage. Preemphasis control is performed in the third and fourth stages, which are part of a filter that emulates the transmitter preemphasis network. A peak clipper at the output of the preemphasis controller provides protection from overmodulation by short duration peaks that are not controlled by the four limiter stages.<
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