Methods and apparatus for post-filtering MDCT domain audio coefficients in a decoder
First Claim
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1. A method of operating a decoder comprising:
- obtaining a vector d(k) comprising quantized Modified Discrete Cosine Transform (MDCT) domain coefficients of a time segment of an audio signal;
deriving a processed vector {circumflex over (d)}(k) by applying a post-filter directly on the vector d(k), the post-filter being configured to have a transfer function H(k),
H(k)={(abs[d(k)])/(max[abs(d)])}a(k),which is a compressed version of an envelope of the vector d(k), where k goes from 1 to the number of MDCT domain coefficients of the time segment of the audio signal, where max[abs(d)] is a maximum of an absolute value of the vector d(k), and a(k) is an emphasis component configured to control a post-filter aggressiveness over the MDCT spectrum; and
deriving a signal waveform by performing an inverse MDCT transform on the processed vector {circumflex over (d)}(k).
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Abstract
Method and decoder for processing of audio signals. The method and decoder relate to deriving a processed vector {circumflex over (d)} by applying a post-filter directly on a vector d comprising quantized MDCT domain coefficients of a time segment of an audio signal. The post-filter is configured to have a transfer function H which is a compressed version of the envelope of the vector d. A signal waveform is reconstructed by performing an inverse MDCT transform on the processed vector {circumflex over (d)}.
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Citations
21 Claims
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1. A method of operating a decoder comprising:
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obtaining a vector d(k) comprising quantized Modified Discrete Cosine Transform (MDCT) domain coefficients of a time segment of an audio signal; deriving a processed vector {circumflex over (d)}(k) by applying a post-filter directly on the vector d(k), the post-filter being configured to have a transfer function H(k),
H(k)={(abs[d(k)])/(max[abs(d)])}a(k),which is a compressed version of an envelope of the vector d(k), where k goes from 1 to the number of MDCT domain coefficients of the time segment of the audio signal, where max[abs(d)] is a maximum of an absolute value of the vector d(k), and a(k) is an emphasis component configured to control a post-filter aggressiveness over the MDCT spectrum; and deriving a signal waveform by performing an inverse MDCT transform on the processed vector {circumflex over (d)}(k). - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A decoder comprising:
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a processor implementing; a filter configured to derive a processed vector {circumflex over (d)}(k) by applying a post-filter directly on a vector d(k), wherein the vector d(k) comprises quantized Modified Discrete Cosine Transform (MDCT) domain coefficients of a time segment of an audio signal, the post-filter being configured to have a transfer function H(k),
H(k)={(abs[d(k)])/(max[abs(d)])}a(k),which is a compressed version of an envelope of the vector d(k), where k goes from 1 to the number of MDCT domain coefficients of the time segment of the audio signal, where max[abs(d)] is a maximum of an absolute value of the vector d(k), and a(k) is an emphasis component configured to control a post-filter aggressiveness over the MDCT spectrum, and a converter configured to derive a signal waveform by performing an inverse MDCT transform on the processed vector {circumflex over (d)}(k). - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. An audio handling entity comprising:
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memory including computer program modules; and a decoder coupled with the memory, the decoder being configured to execute the computer program modules of the memory to, obtain a vector d(k) comprising quantized Modified Discrete Cosine Transform (MDCT) domain coefficients of a time segment of an audio signal, derive a processed vector {circumflex over (d)}(k) by applying a post-filter directly on the vector d(k), the post-filter being configured to have a transfer function H(k),
H(k)={(abs[d(k)])/(max[abs(d)])}a(k),which is a compressed version of an envelope of the vector d(k), where k goes from 1 to the number of MDCT domain coefficients of the time segment of the audio signal, where max[abs(d)] is a maximum of an absolute value of the vector d(k), and a(k) is an emphasis component configured to control a post-filter aggressiveness over the MDCT spectrum, and derive a signal waveform by performing an inverse MDCT transform on the processed vector {circumflex over (d)}(k). - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification