Dolby Laboratories Corporation

Ray Milton Dolby

Paul Anthony Spencer

Philip Charles Plunkett

Noise reduction of a signal such as a video signal is effected by averaging a plurality of relatively delayed replica signals, e.g. with line or field delays therebetween, in a decoding processor, the highly redundant information content of the signal being reinforced by the averaging while random noise undergoes a partial cancellation. In order to overcome the problem of signal changes caused by the decoding processor, the signal is encoded prior to application to the noise-introducing signal channel by a complementary encoding processor in which one or more replica signals are subtractively combined with one or more other replica signals. In both processors a variable combining means is employed to exclude from the combination replica signals which have a non-small difference from the replica signals in the combination, thereby to avoid smearing of the information content (with consequent picture smearing in the case of a video signal) when the signal is changing, e.g. because of movement in a picture.

Systems for reducing noise in video signals using amplitude averaging of

In a stereophonic reproduction system, especially for a cinema, a center channel signal is derived by combining left and right channel signals. In order to harden the center image, particularly in speech, the left and right channel signals are compared and, when they include significant amounts of correlated information, the relative gain of the center channel is enhanced by boosting the gain of that channel and/or cutting the gain of the left and right channels. The test for correlation of information is preferably restricted to speech frequencies and the enhancement of relative gain may be performed only at middle frequencies.

Center channel derivation for stereophonic cinema sound

Compressors and expanders for effecting dynamic range modification are constructed by connecting reactive networks in series for voltage dividing action or in parallel for current dividing action. The output signal is derived from the voltage across or current through one of the networks which includes a series or parallel variable resistance. The variable resistance is controlled in dependence upon the voltage thereacross in the sense required to achieve compression or expansion, as the case may be. The resistance change shifts a turnover frequency of the circuit so as to exclude large amplitude components from the amplitude increase or reduction which is applied to low level components within a restricted frequency band to create the compressor or expander action.

Growing community of inventors

London, United Kingdom

Ray Milton Dolby