Dolby Laboratories Corporation

Arado Electronics

Paul Anthony Spencer

Ray Milton Dolby

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

A metal detector has a balanced coil arrangement fed by an audio frequency oscillator. In-phase and quadrature components arising when the arrangement is unbalanced by proximate conductive objects are detected, the sense of the quadrature component depending on whether the object is ferromagnetic or non-ferromagnetic. The quadrature component varies the frequency of another audio frequency oscillator above and below a mean value and the in-phase component controls the strength of the audio frequency signal fed from the second oscillator to a transducer such as headphones.

Metal detectors for discriminatory detection of buried metal objects

A filter performs a dual filtering function by connecting an input terminal through a first impedance such as a resistor to a first output terminal. The input terminal is connected to a virtual earth at the input to a current amplifier through the first impedance and a second impedance such as a tuned circuit. The output of the amplifier is connected to a second output terminal and also to ground through a third impedance such as a resistor. The characteristics at the first and second output terminals may be complementary band stop and band pass characteristics.

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Paul Anthony Spencer