Compensating filters
First Claim
1. A method of processing an audio signal, said method comprising the steps of:
- executing at least one spectral transform operation to derive a signal spectrum, processing the spectrum to effect smoothing thereof, said smoothing being variable with frequency across the signal spectrum; and
conditioning the response of a filter for use in a subsequent audio reproduction with said smoothed spectrum.
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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.
287 Citations
14 Claims
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1. A method of processing an audio signal, said method comprising the steps of:
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executing at least one spectral transform operation to derive a signal spectrum, processing the spectrum to effect smoothing thereof, said smoothing being variable with frequency across the signal spectrum; and
conditioning the response of a filter for use in a subsequent audio reproduction with said smoothed spectrum. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An acoustic environment audio correction system, comprising:
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a test signal generator;
a measurement microphone;
a conditionable correction filter; and
processing means for deriving a representation of the response of the acoustic environment at a plurality of frequencies in dependence on a test signal generated by the test signal generator and transmitted within the acoustic environment, for processing the representation of the response to effect smoothing, said smoothing being variable with frequency, and subsequently for conditioning the correction filter in dependence on the smoothed representation of the response. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification