Time domain aliasing reduction for non-uniform filterbanks which use spectral analysis followed by partial synthesis

An audio processor for processing an audio signal to acquire a subband representation of the audio signal, the audio processor comprising:

• a cascaded lapped critically sampled transform stage configured to perform a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• a time domain aliasing reduction stage configured to perform a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the first block of samples using at least two window functions, and to acquire at least two segmented sets of subband samples based on the segmented set of bins corresponding to the first block of samples;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the second block of samples using the at least two window functions, and to acquire at least two segmented sets of subband samples based on the segmented set of bins corresponding to the second block of samples;
• and
• wherein the at least two window functions comprise different window width

An audio processor for processing an audio signal to acquire a subband representation of the audio signal, the audio processor comprising:

• a cascaded lapped critically sampled transform stage configured to perform a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• a time domain aliasing reduction stage configured to perform a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the first block of samples using at least two window functions, and to acquire at least two segmented sets of subband samples based on the segmented set of bins corresponding to the first block of samples;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the second block of samples using the at least two window functions, and to acquire at least two sets of subband samples based on the segmented set of bins corresponding to the second block of samples;
• and
• wherein filter slopes of the window functions corresponding to adjacent sets of subband samples are symmetric.

An audio processor for processing a subband representation of an audio signal to acquire the audio signal, the audio processor comprising:

• an inverse time domain aliasing reduction stage configured to perform a weighted combination of two corresponding aliasing reduced subband representations of the audio signal, to acquire an aliased subband representation, wherein the aliased subband representation is a set of subband samples;
• and
• a cascaded inverse lapped critically sampled transform stage configured to perform a cascaded inverse lapped critically sampled transform on the set of subband samples, to acquire a set of samples associated with a block of samples of the audio signal;
• wherein the cascaded inverse lapped critically sampled transform stage comprises a first inverse lapped critically sampled transform stage configured to perform an inverse lapped critically sampled transform on the set of subband samples, to acquire a set of bins associated with a given subband of the audio signal;
• and
• a first overlap and add stage configured to perform a concatenation of sets of bins associated with a plurality of subbands of the audio signal, which comprises a weighted combination of the set of bins associated with the given subband of the audio signal with a set of bins associated with another subband of the audio signal, to acquire a set) of bins associated with a block of samples of the audio signal.

An audio encoder, comprising:

• an audio processor for processing an audio signal to acquire a subband representation of the audio signal, the audio processor comprising:
• a cascaded lapped critically sampled transform stage configured to perform a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• a time domain aliasing reduction stage configured to perform a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein the cascaded lapped critically sampled transform stage comprises a first lapped critically sampled transform stage configured to perform lapped critically sampled transforms on a first block of samples and a second block of samples of the at least two partially overlapping blocks of samples of the audio signal, to acquire a first set of bins for the first block of samples and a second set of bins for the second block of samples;
• wherein the cascaded lapped critically sampled transform stage further comprises a second lapped critically sampled transform stage configured to perform a lapped critically sampled transform on a segment of the first set of bins and to perform a lapped critically sampled transform on a segment of the second set of bins, each segment being associated with a subband of the audio signal, to acquire a set of subband samples for the first set of bins and a set of subband samples for the second set of bins;
• wherein a first set of subband samples is a result of a first lapped critically sampled transform on the basis of the first segment of the first set of bins, wherein a second set of subband samples is a result of a second lapped critically sampled transform on the basis of the second segment of the first set of bins, wherein a third set of subband samples is a result of a third lapped critically sampled transform on the basis of the first segment of the second set of bins, wherein a fourth set of subband samples is a result of a fourth lapped critically sampled transform on the basis of the second segment of the second set of bins;
• and
• wherein the time domain aliasing reduction stage is configured to perform a weighted combination of the first set of subband samples and the third set of subband samples, to acquire a first aliasing reduced subband representation of the audio signal, wherein the time domain aliasing reduction stage is configured to perform a weighted combination of the second set of subband samples and the fourth set of subband samples, to acquire a second aliasing reduced subband representation of the audio signal,
• an encoder configured to encode the aliasing reduced subband representation of the audio signal, to acquire an encoded aliasing reduced subband representation of the audio signal;
• and
• a bitstream former configured to form a bitstream from the encoded aliasing reduced subband representation of the audio signal.

An audio encoder, comprising:

• an audio processor for processing an audio signal to acquire a subband representation of the audio signal, the audio processor comprising:
• a cascaded lapped critically sampled transform stage configured to perform a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• a time domain aliasing reduction stage configured to perform a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the first block of samples using at least two window functions, and to acquire at least two segmented sets of subband samples based on the segmented set of bins corresponding to the first block of samples;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the second block of samples using the at least two window functions, and to acquire at least two sets of subband samples based on the segmented set of bins corresponding to the second block of samples;
• and
• wherein filter slopes of the window functions corresponding to adjacent sets of subband samples are symmetric,
• an encoder configured to encode the aliasing reduced subband representation of the audio signal, to acquire an encoded aliasing reduced subband representation of the audio signal;
• and
• a bitstream former configured to form a bitstream from the encoded aliasing reduced subband representation of the audio signal.

An audio analyzer, comprising:

• an audio processor for processing an audio signal to acquire a subband representation of the audio signal, the audio processor comprising:
• a cascaded lapped critically sampled transform stage configured to perform a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• a time domain aliasing reduction stage configured to perform a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein the cascaded lapped critically sampled transform stage comprises a first lapped critically sampled transform stage configured to perform lapped critically sampled transforms on a first block of samples and a second block of samples of the at least two partially overlapping blocks of samples of the audio signal, to acquire a first set of bins for the first block of samples and a second set of bins for the second block of samples;
• wherein the cascaded lapped critically sampled transform stage further comprises a second lapped critically sampled transform stage configured to perform a lapped critically sampled transform on a segment of the first set of bins and to perform a lapped critically sampled transform on a segment of the second set of bins, each segment being associated with a subband of the audio signal, to acquire a set of subband samples for the first set of bins and a set of subband samples for the second set of bins;
• wherein a first set of subband samples is a result of a first lapped critically sampled transform on the basis of the first segment of the first set of bins, wherein a second set of subband samples is a result of a second lapped critically sampled transform on the basis of the second segment of the first set of bins, wherein a third set of subband samples is a result of a third lapped critically sampled transform on the basis of the first segment of the second set of bins, wherein a fourth set of subband samples is a result of a fourth lapped critically sampled transform on the basis of the second segment of the second set of bins;
• and
• wherein the time domain aliasing reduction stage is configured to perform a weighted combination of the first set of subband samples and the third set of subband samples, to acquire a first aliasing reduced subband representation of the audio signal, wherein the time domain aliasing reduction stage is configured to perform a weighted combination of the second set of subband samples and the fourth set of subband samples, to acquire a second aliasing reduced subband representation of the audio signal;
• and
• an information extractor, configured to analyze the aliasing reduced subband representation, to provide an information describing the audio signal.

An audio analyzer, comprising:

• an audio processor for processing an audio signal to acquire a subband representation of the audio signal, the audio processor comprising:
• a cascaded lapped critically sampled transform stage configured to perform a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• a time domain aliasing reduction stage configured to perform a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the first block of samples using at least two window functions, and to acquire at least two segmented sets of subband samples based on the segmented set of bins corresponding to the first block of samples;
• wherein the cascaded lapped critically sampled transform stage is configured to segment a set of bins acquired on the basis of the second block of samples using the at least two window functions, and to acquire at least two sets of subband samples based on the segmented set of bins corresponding to the second block of samples;
• and
• wherein filter slopes of the window functions corresponding to adjacent sets of subband samples are symmetric;
• and
• an information extractor, configured to analyze the aliasing reduced subband representation, to provide an information describing the audio signal.

A method for processing an audio signal to acquire a subband representation of the audio signal, the method comprising:

• performing a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• performing a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein performing the cascaded lapped critically sampled transform comprises performing lapped critically sampled transforms on a first block of samples and a second block of samples of the at least two partially overlapping blocks of samples of the audio signal, to acquire a first set of bins for the first block of samples and a second set of bins for the second block of samples;
• wherein performing the cascaded lapped critically sampled transform comprises performing a lapped critically sampled transform on a segment of the first set of bins and performing a lapped critically sampled transform on a segment of the second set of bins, each segment being associated with a subband of the audio signal, to acquire a set of subband samples for the first set of bins and a set of subband samples for the second set of bins;
• wherein a first set of subband samples is a result of a first lapped critically sampled transform on the basis of the first segment of the first set of bins, wherein a second set of subband samples is a result of a second lapped critically sampled transform on the basis of the second segment of the first set of bins, wherein a third set of subband samples is a result of a third lapped critically sampled transform on the basis of the first segment of the second set of bins, wherein a fourth set of subband samples is a result of a fourth lapped critically sampled transform on the basis of the second segment of the second set of bins;
• and
• wherein performing the weighted combination of two corresponding sets of subband samples comprises performing a weighted combination of the first set of subband samples and the third set of subband samples, to acquire a first aliasing reduced subband representation of the audio signal, wherein the time domain aliasing reduction stage is configured to perform a weighted combination of the second set of subband samples and the fourth set of subband samples, to acquire a second aliasing reduced subband representation of the audio signal.

A method for processing an audio signal to acquire a subband representation of the audio signal, the method comprising:

• performing a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• performing a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein performing the cascaded lapped critically sampled transform comprises segmenting a set of bins acquired on the basis of the first block of samples using at least two window functions, and acquiring at least two segmented sets of subband samples based on the segmented set of bins corresponding to the first block of samples;
• wherein performing the cascaded lapped critically sampled transform comprises segmenting a set of bins acquired on the basis of the second block of samples using the at least two window functions, and acquiring at least two segmented sets of subband samples based on the segmented set of bins corresponding to the second block of samples;
• and
• wherein the at least two window functions comprise different window width.

A method for processing an audio signal to acquire a subband representation of the audio signal, the method comprising:

• performing a cascaded lapped critically sampled transform on at least two partially overlapping blocks of samples of the audio signal, to acquire a set of subband samples on the basis of a first block of samples of the audio signal, and to acquire a corresponding set of subband samples on the basis of a second block of samples of the audio signal;
• and
• performing a weighted combination of two corresponding sets of subband samples, one acquired on the basis of the first block of samples of the audio signal and one acquired on the basis on the second block of samples of the audio signal, to acquire an aliasing reduced subband representation of the audio signal;
• wherein performing the cascaded lapped critically sampled transform comprises segmenting a set of bins acquired on the basis of the first block of samples using at least two window functions, and acquiring at least two segmented sets of subband samples based on the segmented set of bins corresponding to the first block of samples;
• wherein performing the cascaded lapped critically sampled transform comprises segmenting a set of bins acquired on the basis of the second block of samples using the at least two window functions, and acquiring at least two sets of subband samples based on the segmented set of bins corresponding to the second block of samples;
• and
• wherein filter slopes of the window functions corresponding to adjacent sets of subband samples are symmetric.

A method for processing a subband representation of an audio signal to acquire the audio signal, the method comprising:

• performing a weighted combination of two corresponding aliasing reduced subband representations of the audio signal, to acquire an aliased subband representation, wherein the aliased subband representation is a set of subband samples;
• and
• performing a cascaded inverse lapped critically sampled transform on the set of subband samples, to acquire a set of samples associated with a block of samples of the audio signal;
• wherein performing the cascaded inverse lapped critically sampled transform comprises performing an inverse lapped critically sampled transform on the set of subband samples, to acquire a set of bins associated with a given subband of the audio signal;
• and
• wherein performing the cascaded inverse lapped critically sampled transform comprises performing a concatenation of sets of bins associated with a plurality of subbands of the audio signal, which comprises a weighted combination of the set of bins associated with the given subband of the audio signal with a set of bins associated with another subband of the audio signal, to acquire a set of bins associated with a block of samples of the audio signal.