Abstract: A multiband compressor suitable for compressing the dynamic range of an audio signal in a broadcasting system is disclosed. The frequency band with the highest predictable energy is selected as a master band with the energy level in this band used to control the gain in the other (slave) bands. When the energy in a slave band exceeds a predetermined level, additional control of the signal level in that band occurs. The described compressor has the advantages of both the wideband compressors and multiband compressors without the disadvantages of these compressors. In addition to the compressor, a unique overshoot protection circuit is described.

Abstract: A circuit which provides a control signal to dynamically adjust the level of clipping for an audio signal is described. The criterion for allowable clipping employed by the circuit is whether the clipper induced distortion is noticeable; the clipper induced distortion may be audible, however, remain unnoticeable. A frequency weighted correlation is performed on the audio signal to evaluate the waveform and establish an unnoticeable level of clipping.

Abstract: A circuit for controlling the polarity of an asymmetrical waveform, such as a typical audio waveform, is described. The circuit provides smooth polarity switching with substantially no audible switching sound. The smooth switching results from switching each frequency of the audio signal at a different time. The circuit is particularly useful in a peak-limiting apparatus such as those often used in AM broadcasting.

Abstract: A peak-limiting apparatus and method particularly useful in systems employing high frequency pre-emphasis to compensate for steep high frequency rolloff in a receiver, or the like. The apparatus and method is useful in standard AM broadcasting to maximize loudness without noticeable distortion. The distortion caused by a clipper is determined by subtracting a clipper's output from its input. This distortion is compared in a plurality of critical bands with the input to provide a gain control feedback signal for a variable gain stage. The psychoacoustic phenomenon of "masking" is used to estimate maximum (non-audible) clipping.

Abstract: In a bandlimited recording or transmission system utilizing broadband limiting and high-frequency pre-emphasis followed by clipping, a unique combination of a lowpass filter and shelving filter are used to limit channel overload exhibited by prior art clipping and anti-aliasing filters. The pre-emphasis employs a split path signal flow, with a voltage controlled amplifier used on the high-frequency signal path.

Abstract: A reverberation system which employs low cost, spring reverberators and obtains a frequency response to beyond 9kHz. The high frequency components of an input signal are frequency shifted, to a lower range, applied to a reverberator, and then frequency shifted to their original range. This signal is then summed with the output of a second reverberator which receives the lower frequency components of the input signal.