Thorn Emi Plc

Central Research Laboratories Limited

Stuart John Best

Martin Peter Todd

Nigel Johnson

Adrian M Sandford

Timothy Poole

Ian Robert McLauchlan

Reginald A Willard

Apparatus for labelling a stereophonic signal includes a plurality of notch filters having selected center frequencies to form notches at the selected frequencies in the channels of a stereophonic audio signal. Code generating components produce a coded label signal in the form of one or more code words, with the code being formed of selected signal bursts at the selected frequencies. The coded label signals are inserted into both channels of the audio signal, in the notches formed by the notch filters. The code signal amplitude bears a predetermined relationship to the audio signal amplitude in each channel.

Audio signal identification using digital labelling signals

A signal identification system, suitable for producing an identification code on a sound track recording is described. The system includes an encoder 209 effective to eliminate a variable sequence of frequency bands from an audio signal and insert a sequence of code signals into the frequency bands. As the sequence of frequency bands varies throughout the sound track recording, the presence of the code is difficult to detect.

Signal identification system

Equipment for labelling audio signals with identification information has an encoder which inserts the binary information into two very narrow notches of center frequencies 2883 and 3417 Hz, between semi-tones in the tonic scale to minimize music breakthrough into the decoding circuits, and to ensure that no fundamental frequencies in the tonic scale will be excluded in the reproduction. The notches are derived from a 3-stage biquad filter, and are approximately 50 dB deep and 150 Hz wide at the top. The encoder includes a wide bandpass circuit consisting of a 1 KHz highpass filter and a 6 KHz lowpass filter introduced to ensure that the code insertion level is not determined by frequencies, either high or low, which do not adequately mask the code frequencies. The code amplitude is kept a fixed level below the programme, initially adjustable by a suitable control. The code sequence has an addressing pre-amble consisting of a simultaneous burst of both the lower and higher frequencies for a period of 8 digits, followed by a message portion of 40 bits formed of an appropriate stream of the two frequencies.

Signal identification

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Harlington, United Kingdom

Stuart John Best