PITCH-BASED PRE-FILTERING AND POST-FILTERING FOR COMPRESSION OF AUDIO SIGNALS
First Claim
1. A system for enhancing the quality of an audio signal produced by an audio codec, comprising:
- a pitch-based pre-filter that adaptively filters an input audio signal to produce a filtered audio signal, wherein adaptively filtering the input audio signal comprises filtering each of a plurality of segments of the input audio signal in a manner that is dependent upon an estimated pitch period associated therewith;
an audio encoder that encodes the filtered audio signal to generate a compressed audio bit stream;
an audio decoder that decodes the compressed audio bit stream to generate a decoded audio signal; and
a pitch-based post-filter that adaptively filters the decoded audio signal to produce an output audio signal, wherein adaptively filtering the decoded audio signal comprises filtering each of a plurality of segments of the decoded audio signal in a manner that is dependent upon an estimated pitch period associated therewith, and wherein the pitch-based post-filter operates to undo at least part of a signal-shaping effect of the pitch-based pre-filter.
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Accused Products
Abstract
Systems and methods for enhancing the quality of an audio signal produced by an audio codec are described herein. In accordance with the systems and methods, a pitch-based pre-filter adaptively filters an input audio signal to produce a filtered audio signal. An audio encoder encodes the filtered audio signal to generate a compressed audio bit stream. An audio decoder decodes the compressed audio bit stream to generate a decoded audio signal. A pitch-based post-filter adaptively filters the decoded audio signal to produce an output audio signal, wherein adaptively filtering the decoded audio signal comprises undoing at least part of a signal-shaping effect of the pitch-based pre-filter.
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Citations
21 Claims
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1. A system for enhancing the quality of an audio signal produced by an audio codec, comprising:
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a pitch-based pre-filter that adaptively filters an input audio signal to produce a filtered audio signal, wherein adaptively filtering the input audio signal comprises filtering each of a plurality of segments of the input audio signal in a manner that is dependent upon an estimated pitch period associated therewith; an audio encoder that encodes the filtered audio signal to generate a compressed audio bit stream; an audio decoder that decodes the compressed audio bit stream to generate a decoded audio signal; and a pitch-based post-filter that adaptively filters the decoded audio signal to produce an output audio signal, wherein adaptively filtering the decoded audio signal comprises filtering each of a plurality of segments of the decoded audio signal in a manner that is dependent upon an estimated pitch period associated therewith, and wherein the pitch-based post-filter operates to undo at least part of a signal-shaping effect of the pitch-based pre-filter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for enhancing the quality of an audio signal produced by an audio codec, comprising:
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filtering each of a plurality of segments of an input audio signal by a pitch-based pre-filter in a manner that is dependent upon an estimated pitch period associated therewith to produce a filtered audio signal; encoding the filtered audio signal in an audio encoder to generate a compressed audio bit stream; and providing the compressed audio bit stream to a system that includes an audio decoder that decodes the compressed audio bit stream to generate a decoded audio signal and a pitch-based post-filter that filters each of a plurality of segments of the decoded audio signal in a manner that is dependent upon an estimated pitch period associated therewith to undo at least part of a signal-shaping effect of the pitch-based pre-filter. - View Dependent Claims (14, 15)
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16. A method for enhancing the quality of an audio signal produced by an audio codec, comprising:
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receiving a compressed audio bit stream generated by a system that includes a pitch-based pre-filter that filters each of a plurality of segments of an input audio signal in a manner that is dependent upon an estimated pitch period associated therewith to produce a filtered audio signal and an audio encoder that encodes the filtered audio signal to generate the compressed audio bit stream; decoding the compressed audio bit stream in an audio decoder to generate a decoded audio signal; and filtering each of a plurality of segments of the decoded audio signal by a pitch-based post-filter in a manner that is dependent upon an estimated pitch period associated therewith to produce an output audio signal, wherein the filtering operates to undo at least part of a signal-shaping effect of the pitch-based pre-filter. - View Dependent Claims (17, 18)
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19. A method for avoiding frame boundary discontinuities when performing pitch-based pre-filtering and pitch-based post-filtering of an audio signal, comprising:
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(a) obtaining a first set of filter parameters associated with a previously-received frame of the audio signal, wherein at least one parameter in the first set of filter parameters is determined based on an estimated pitch period associated with the previously-received frame; (b) obtaining a second set of filter parameters associated with a current frame of the audio signal, wherein at least one parameter in the second set of filter parameters is determined based on an estimated pitch period associated with the current frame; and (c) for each of a predetermined number of samples at a beginning of the current frame, consecutively performing an operation that effectively calculates and overlap adds a first filtered audio signal sample that corresponds to the sample of the current frame and is obtained using the first set of filter parameters and a second filtered audio signal sample that corresponds to the sample of the current frame and is obtained using the second set of filter parameters, thereby obtaining a corresponding sample of a filter output signal. - View Dependent Claims (20)
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21. A system, comprising:
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an audio encoder that includes; a band splitter that splits an input audio signal into at least a first sub-band audio signal and a second sub-band audio signal, a pitch-based pre-filter that filters the first sub-band audio signal to produce a pre-filtered first sub-band audio signal, a first sub-band encoder that encodes the pre-filtered first sub-band audio signal to produce an encoded first sub-band audio signal, a second sub-band encoder that encodes the second sub-band audio signal to produce an encoded second sub-band audio signal, and a bit multiplexer that combines at least the encoded first sub-band audio signal and the encoded second sub-band audio signal to generate a compressed audio bit stream; and an audio decoder that includes; a bit demultiplexer that obtains at least the encoded first sub-band audio signal and the encoded second sub-band audio signal from the compressed audio bit stream, a first sub-band decoder that decodes the encoded first sub-band audio signal to produce a decoded first sub-band audio signal, a second sub-band decoder that decodes the encoded second sub-band audio signal to produce a decoded second sub-band audio signal, a pitch-based post-filter that filters the decoded first sub-band audio signal to produce a post-filtered decoded first sub-band audio signal, and a band combiner that combines at least the post-filtered decoded first sub-band audio signal and the decoded second sub-band audio signal to produce an output audio signal.
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Specification