Abstract: A circuit and method for compressing or generating a pulse, particularly a chirp pulse, which uses infinite impulse response filtering (3.2). The infinite impulse response filters (3.9, 3.10, 3.11, 3.12) simulate the responses of finite impulse response filters. This is achieved by pre-processing the signal by passing it through a pre-processing filter (3.3) which has zero response at the resonant frequencies of the infinite impulse response filters (3.9, 3.10, 3.11, 3.12). The pre-processing and infinite impulse response filtering may be incorporated into a matched filter for detection of a chirp waveform input signal. This can be implemented in the time domain or the frequency domain. The matched filter also can incorporate beating to the base band techniques. The matched filter can also act as a generator by applying a pulse to the input which has the unit impulse function causing a chirp signal, equivalent to the transfer function of the filter, to be produced as the output.

Abstract: Apparatus for processing a broadband signal, 1.2, 2.2, by determining the first and second moments of variation between frequency sub-bands, 1.4, 2.4, of the broadband signal, 1.2, 2.2, in order to either distinguish between man made objects and natural objects or detect shadows comprising splitters, 1.3, 2.3, which comprise analogue or digital filters, for separating the broadband signal into a plurality of frequency sub-band signals, 1.4, 2.4, detectors means, 1.5, 2.5, for processing each of the frequency sub-band signals, 1.4, 2.4, to either extract, identify or enhance a signal within the broadband signal, 1.2, 2.2, and combiners, 1.7, 2.7, for re-combining the processed frequency sub-band signals, 1.4, 2.4, by either summating the frequency sub-band signals, 1.4, 2.4, to produce the first moment of variation or enabling the amount of variation between the processed frequency sub-band signals, 1.4, 2.4, to be analyzed to produce the second moment of variation.

Abstract: Apparatus for improving the audibility of incident sound (4) to a person (3) operating in an environment where there is a substantial background noise field (2) coming from a source (1) of repetitive noise, comprises an adaptable waveform generator (7), a first electro-acoustic transducer (10) receiving a synthesized cancelling waveform from the generator (7) and generating a cancelling noise to at least partly null the background noise, a second electro-acoustic transducer (11) to sense the partially nulled background noise, and adaptor (13) to modify the output of the generator (7) on the basis of the electrical output signal from the second transducer to minimize the nulled background noise, and sensor (5) to feed a triggering signal (6) derived from the source to the waveform generator. The electro-acoustic transducers (10, 11) can be mounted in headset (8) holding the transducers adjacent to an ear of said person without substantially impeding the arrival of said incident sound (4) to said ear.

Abstract: Vibration isolation between a source (1) and a mounting (3) is provided by means of a vibration-cancelling actuator (4a) with a shear isolator (5) placed in series with the source (1). Mechanical and magnetic actuators are disclosed, a preferred mechanical actuator including its own shear isolation with a ratio of compliance in shear and axial directions of at least 50:1.

Abstract: Primary vibrations from a repetitive source of such vibrations are nulled in a location by specially generated secondary vibrations fed to the location from an actruator. The actuator is driven by a waveform generator which is synchronized to the source by a synchronizing signal on the line which is derived otherwise than from the source. In FIG. 2, the synchronizing signal is derived from the output of a residual vibration sensor via a filter or a phase-locked loop (FIG. 3 and 4).

Abstract: Methods and apparatus for cancelling both random and repetitive vibrations in gases, liquids or solids. The invention relies on generating cancelling vibrations (S) for a primary vibration to be nulled (P) by operating at discrete locations in the frequency domain of time samples of the waveform of the primary vibration. The cancelling vibrations required are generated by transforming (at 15) the sensed residual vibrations into a plurality of pairs of components which together define the residual vibrations at a plurality of different locations in the frequency domain, separately modifying (at 17) the independent components and then transforming (at 20) the modified components back into a drive signal for the source (12) of the cancelling vibrations.

Abstract: A method of reducing the adaption time needed to adapt a synthetically generated secondary waveform so that it nulls a primary repetitive waveform (e.g. noise) from a source (1) of vibration, the secondary waveform generation (5) being synchronized by the source (1). The clarity and/or the amplitude of at least a part of the signal resulting from interaction between the primary and secondary waveforms is sensed (6) and used (7, 8) to reshape the secondary waveform. The invention finds application in the cancelling of repetitive vibrations (e.g. in quietening the driving cab of a vehicle).

Abstract: This invention concerns a method of, and apparatus for, reducing the ambient noise level at a location in the vicinity of a source of recurring noise. In its preferred embodiments the invention involves generating a series of cancelling noise signals which are exactly synchronized with the bursts of recurring noise from the source and adapting the cancelling signals in the series on the basis of the success achieved in nulling the noise from the source at the location.