Abstract: When a video signal including a component modulated onto a subcarrier (such as a PAL signal) is subjected to a non-linear pre-emphasis known for MAC signals, with the object of reducing the effects of noise encountered in transmitting the composite signal through an f.m. channel, problems of noise and differential gain remain. These problems are overcome by subjecting the composite signal to a filtering step, before application of the non-linear processing, so as to filter out the subcarrier, the chrominance subcarrier in a PAL signal, and to compand the chrominance sidebands. Preferably a notch filter is used which has a notch shaped as a Gaussian curve.

Abstract: A method of pre-emphasising a signal comprises the steps of a) receiving the signal as an input; b) applying the input signal to a processing system comprising a pair of parallel signal processing paths each comprising a non-linear phase filter and a non-linearity, and a further parallel path, wherein the filters in the pair of processing paths have equal but opposite phase responses and substantially equal magnitude responses, and wherein the outputs of the parallel processing paths are combined to produce the raw pre-emphasised signal; whereby the input signal is subjected to a non-linear dynamic range compression which is phase linear. Alternatively or additionally the input signal is split into at least three different frequency bands for non-linear processing. Preferably the pre-emphasised signal is pre-corrected using an iterative system. Complementary de-emphasis systems are also described, as well as pre-emphasis and de-emphasis apparatus.

Abstract: In a high definition multiplexed analog component system, a high definition signal is processed by splitting it into high and low frequency components and pre-emphasizing the high frequency component with a non-linear characteristic and at the receiver a complementary de-emphasis process is applied to produce a noise-reduced high definition signal compatible with existing conventional receivers. A processor of a pre-connector for the high definition signal can be used for intersample interference due to non-compatibility between the pre and de-emphasis characteristics in a digital implementation of the system.

Abstract: A phase lock loop demodulator has its loop transfer function (F(s)) optimized to: F(s)=A+B/s+CF.sub.1 (s)+DF.sub.2 (s) where CF.sub.1 (s) is a chrominance sub-carrier term DF.sub.2 (s) is a sound sub-carrier term and A, B, C and D are constants whereby to minimize the phase error signal appearing at the output of the phase comparator (10) of the loop. An equalizer circuit (14) may be added at the output of the loop in which case the transfer function (F.sub.T (s)) of the equalizer circuit is as follows: F.sub.T (s)=KoKd+s/F(s) where F(s) is the transfer function of the loop amplifier circuit (12) and A, Ko and Kd are constants.

Abstract: In a system in which an information signal is transmitted along with digital data from a transmitter to a receiver, transmitter circuitry is provided which produces digital data indicative of parameters relating to noise reduction for the information signal, and receiver circuitry is provided responsive to the digital data so as to optimize reception of the information signal. In one embodiment of the invention, one of a plurality of different pre-emphasis levels is applied to a signal and digital data is produced according to a value of pre-emphasis added. The digital data and the pre-emphasized signal are then transmitted. The receiver decodes the digital data and adds a corresponding amount of de-emphasis to the received information signal. In another embodiment the digital data indicates an optimum value for a parameter to be applied to a threshold extension demodulator in the receiver.

Abstract: A demodulator for television signals includes a feedback loop which incorporates a delay for feeding back a first portion of a modulating signal to be compared with a following portion of the signal. This allows correlation of the modulating signals between the first portion of the signal and the following portion. Such correlation can be applied in feedback type demodulation such as phase-locked loops, to increase the threshold performance of the loop. The circuitry can be applied in normal demodulation circuits to effect a frequency tracking circuit allowing the use of a band pass filter with a narrower band than would be normally allowable.

Abstract: A phase lock loop demodulator has its loop amplifier and filter designed such that the transfer function of the amplifier and filter is optimized for the presence of sound and color subcarriers. An equalizer circuit is included in the demodulator for equalizing the demodulator response and has a transfer function which is independent of the transfer function of the loop filter and amplifier whereby to render the demodulator insensitive to small frequency errors around the subcarrier frequencies.