Electrical audio signal processing systems and devices – Noise or distortion suppression – Interpolation
Patent
1981-04-16
1983-11-22
Rubinson, G. Z.
Electrical audio signal processing systems and devices
Noise or distortion suppression
Interpolation
381 95, 381 43, H04B 1500
Patent
active
044170980
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an "active attenuation" method of cancelling noise (or other vibration) in which a primary vibration entering a selected location is nulled or cancelled by means of a secondary vibration which is fed into the location to reduce (and at best eliminate), the influence of the primary vibration. An accurate matching of phase and amplitude of the secondary vibration to the primary vibration is necessary if effective nulling is to result. In particular this invention is concerned with repetitive primary vibrations such as arise, for example, with an internal combustion engine.
BACKGROUND ART
In the specification of U.S. Pat. No. 4,153,815 there is described a method for the reduction of unwanted vibrations received at a selected location from a source of recurring vibrations which method comprised feeding a specially synthesised secondary vibration to said location, the generation of the secondary vibration being triggered by a signal derived from the source, and the waveform of the synthesised secondary vibration being adapted with respect to time to improve the extent to which the secondary vibration nulls the primary vibration at the said location.
DISCLOSURE OF INVENTION
The present invention relates to an adaptive method similar to that described in the preceding paragraph but which is characterised in that the time taken to evolve a successful adaption of the secondary vibration is reduced by monitoring the contemporary residual vibration at the said location which results from interaction between the primary vibration and the contemporary secondary vibration, and effecting the adaption of the secondary vibration on the basis of the amplitude and/or the polarity of at least a part of the contemporary residual vibration.
Suitably the amplitude and/or the polarity of each pulse of the residual vibration is cyclically sensed in a plurality of successive time intervals, each separate sensing being separately used in the correct sequence to control the adaption of a different part of the secondary vibration.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be further described, by way of example, with reference to the accompanying drawings, in which
FIG. 1 is a schematic illustration of the broad principles behind the method of the invention,
FIG. 2 is a block diagram illustrating one embodiment of waveform generator as shown in FIG. 1,
FIG. 3 is a schematic indication of the principle for the fast adaption achieved by the method of the invention,
FIG. 4 shows three graphs of actual and simulated waveforms,
FIG. 5 is a schematic illustration of a first embodiment of apparatus for carrying out the method of the invention,
FIG. 6 is a graph illustrating how delay is compensated for in the method of the invention,
FIG. 7 and 8 are schematic illustrations of second and third embodiments of apparatus for carrying out the method of the invention,
FIGS. 9 and 10 are graphs illustrating the performance obtainable with the method of the invention, and
FIG. 11 is a schematic illustration of a fourth embodiment of apparatus for carrying out the method of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
In the following description reference will be made to the cancellation of noise (i.e. acoustic vibrations in air) but it should be understood that the invention is equally applicable to the cancellation of vibration in gases, liquids or solids.
FIG. 1 shows a source 1 of a recurring noise which is nulled in a protected area 4 by a secondary vibration generated by a transducer (e.g. a loudspeaker) 3. A waveform generator 5 powers the transducer 3 and the output of this generator 5 is synchronised with the noise generation by a transducer 2 on the source 1. A microphone 6 in the area 4 senses the residula sound and feeds this to a control unit 7 which controls an adaptation unit 8 used to modify the output waveform of the generator 5 and thus seek for total cancellation in the area 4.
One form of generator 5 and adaptation unit 8 which can be used in the syste
REFERENCES:
patent: 3492563 (1970-01-01), Myer
patent: 3818364 (1974-06-01), Barret
patent: 4122303 (1978-10-01), Chaplin et al.
patent: 4153815 (1979-05-01), Chaplin et al.
Chaplin George B. B.
Powell Andrew R.
Smith Roderick A.
Dwyer James L.
Rubinson G. Z.
Sound Attenuators Limited
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