Abstract: A circuit for providing enhanced stereophonic sound by processing the L-R signal. A compressor which receives the L+R signal provides a gain control signal. This signal controls the level of the L-R signal and the gain in a tracking VCA. The tracking VCA receives the enhanced L-R signal and under predetermined conditions prevents increasing the level of the L-R signal.

Abstract: Improved FMX Companding apparatus for FM transmitter. A pilot subsystem which is substantially identical to the FMX audio path is used to develop a control signal which provides amplitude control through a VCA in the main FMX audio path.

Abstract: A peak limiter is described which employs the Hilbert transform. Effectively distinct processing occurs for low frequency and high frequency signals and harmonic distortion results only when the limiter is excited by high frequencies.

Abstract: A peak limiter is described which employs the Hilbert transform. Effectively distinct processing occurs for low frequency and high frequency signals and harmonic distortion results only when the limiter is excited by high frequencies.

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 multiband analog audio processor is described which provides low peak-to-r.m.s. ratios. A distributed crossover configuration is described which, in the presently preferred embodiment, employs bandpass filters with embedded clippers for high frequency processing. Circuits for improved distortion performance of the distributed crossover configuration is also described. An economical series/parallel crossover configuration with favorable summation properties is also set forth.

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 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.