Compensating filters
First Claim
1. Apparatus for generating an audio test signal comprising means (8) for generating a periodically repeating signal with a broad band frequency content and a periodically varying phase, in which the phase repetition period exceeds the signal repetition period.
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Accused Products
Abstract
A prefilter (5) for an audio system comprising a loudspeaker (1) in a room (2), which corrects both amplitude and phase errors due to the loudspeaker (1) by a linear phase correction filter response and corrects the amplitude response of the room (2) whilst introducing the minimum possible amount of extra phase distortion by employing a minimum phase correction filter stage. A test signal generator (8) generates a signal comprising a periodic frequency sweep with a greater phase repetition period than the frequency repetition period. A microphone (7) positioned at various points in the room (2) measures the audio signal processed by the room (2) and loudspeaker (1), and a coefficient calculator (6) (e.g. a digital signal processor device) derives the signal response of the room and thereby a requisite minimum phase correction to be cascaded with the linear phase correction already calculated for the loudspeaker (1). Filter (5) may comprise the same digital signal processor as the coefficient calculator (6). Applications in high fidelity audio reproduction, and in car stereo reproduction.
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Citations
22 Claims
- 1. Apparatus for generating an audio test signal comprising means (8) for generating a periodically repeating signal with a broad band frequency content and a periodically varying phase, in which the phase repetition period exceeds the signal repetition period.
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14. A method of testing the audio response of a system, comprising applying a periodically repeating signal thereto, the periodically repeating signal being such that the frequency components thereof are arranged not to be harmonically related, and measuring the output thereof in response to application of said signal, and separating from said measured output said signal components, separately of harmonics thereof introduced by distortion.
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15. A method of audio response measurement, comprising applying a signal portion to a system under test several times in a sequence, the phase of said signal being different at each repetition in the sequence, and producing from said sequence an averaged signal response by averaging each portion of signal over said different phases to reduce the effects of harmonic distortion.
- 18. An audio test signal having a periodic repetition period, a broad band frequency content and a periodically varying phase, the phase repetition period exceeding the periodic repetition period.
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20. An audio processing apparatus for cooperation with a predetermined loudspeaker which comprises:
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means for generating a periodically varying audio test signal through said loudspeaker, said periodically varying signal having a broad band frequency content and a periodically varying phase, in which the phase repetition period exceeds the signal repetition period; means for connection to an audio input device to receive said audio test signal and to derive a measured response; filter means arranged to filter an audio signal supplied to the loudspeaker in accordance with a plurality of filter parameters; and means for deriving the parameters of the filter means, wherein the apparatus further comprises; means for storing data relating to the loudspeaker signal response; and
in that the parameters of the filter means are derived in a manner jointly responsive to said stored data and to said measured response. - View Dependent Claims (21, 22)
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Specification