MDCT-based complex prediction stereo coding
First Claim
1. A decoder system for providing a stereo signal by complex prediction stereo coding, the decoder system comprising:
- an upmix stage adapted to generate the stereo signal based on first frequency-domain representations of a downmix signal and a residual signal, each of the first frequency-domain representations comprising first spectral components representing spectral content of the corresponding signal expressed in a first subspace of a multidimensional space, the upmix stage comprising;
a module for computing a second frequency-domain representation of the downmix signal based on the first frequency-domain representation thereof, the second frequency-domain representation comprising second spectral components representing spectral content of the signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace;
a weighted summer for computing a side signal on the basis of the first and second frequency-domain representations of the downmix signal, the first frequency-domain representation of the residual signal and a complex prediction coefficient encoded in a bit stream signal received by the decoder system; and
a sum-and-difference stage for computing the stereo signal on the basis of the first frequency-domain representation of the downmix signal and the side signal,wherein the upmix stage is further operable in a pass-through mode, in which said downmix and residual signals are supplied to the sum-and-difference stage directly.
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Abstract
The invention provides methods and devices for stereo encoding and decoding using complex prediction in the frequency domain. In one embodiment, a decoding method, for obtaining an output stereo signal from an input stereo signal encoded by complex prediction coding and comprising first frequency-domain representations of two input channels, comprises the upmixing steps of: (i) computing a second frequency-domain representation of a first input channel; and (ii) computing an output channel on the basis of the first and second frequency-domain representations of the first input channel, the first frequency-domain representation of the second input channel and a complex prediction coefficient. The upmixing can be suspended responsive to control data.
16 Citations
30 Claims
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1. A decoder system for providing a stereo signal by complex prediction stereo coding, the decoder system comprising:
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an upmix stage adapted to generate the stereo signal based on first frequency-domain representations of a downmix signal and a residual signal, each of the first frequency-domain representations comprising first spectral components representing spectral content of the corresponding signal expressed in a first subspace of a multidimensional space, the upmix stage comprising; a module for computing a second frequency-domain representation of the downmix signal based on the first frequency-domain representation thereof, the second frequency-domain representation comprising second spectral components representing spectral content of the signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace; a weighted summer for computing a side signal on the basis of the first and second frequency-domain representations of the downmix signal, the first frequency-domain representation of the residual signal and a complex prediction coefficient encoded in a bit stream signal received by the decoder system; and a sum-and-difference stage for computing the stereo signal on the basis of the first frequency-domain representation of the downmix signal and the side signal, wherein the upmix stage is further operable in a pass-through mode, in which said downmix and residual signals are supplied to the sum-and-difference stage directly. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An encoder system for encoding a stereo signal using complex prediction as a signal comprising downmix and residual channels and a complex prediction coefficient, wherein the downmix and residual channels are segmented into time frames, said system including:
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an estimator for estimating a complex prediction coefficient; a coding stage operable; (a) to transform the stereo signal into a frequency-domain representation of a downmix and a residual signal, in a relationship determined by the value of the complex prediction coefficient; and (b) to act as a pass-through stage, thereby supplying as output the stereo signal to be encoded, the encoder system further comprising a switch for selecting, for each time segment, whether to encode the stereo signal in this time segment by at least one of the following options; direct stereo coding, joint stereo coding, and complex-prediction stereo coding, wherein, if direct stereo coding is selected, the coding stage is configured to transform the stereo signal into a frequency-domain representation of a left channel and a right channel, which are encoded as a bit stream; and wherein, if joint stereo coding is selected, the coding stage is configured to transform the stereo signal into a frequency-domain representation of a downmix and side channel, which are encoded as a bit stream. - View Dependent Claims (13, 14)
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15. A decoding method implemented in a decoder system for providing a stereo signal by complex prediction stereo coding, the method comprising the steps of:
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receiving first frequency-domain representations of a downmix signal and a residual signal, each of the first frequency-domain representations comprising first spectral components representing spectral content of the corresponding signal expressed in a first subspace of a multidimensional space; receiving a control signal; and responsive to the value of said control signal; (a) upmixing said downmix and residual signals, using an upmix stage, to obtain said stereo signal, by performing the sub-steps of; computing a second frequency-domain representation of the downmix signal based on the first frequency-domain representation thereof, the second frequency-domain representation comprising second spectral components representing spectral content of the signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace; computing a side signal on the basis of the first and second frequency-domain representations of the downmix signal, the first frequency-domain representation of the residual signal and a complex prediction coefficient encoded in a bit stream signal received by the decoder system; and computing said stereo signal by applying a sum-and-difference transform to the first frequency-domain representation of the downmix signal and the side signal, or (b) suspending upmixing. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 29)
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24. An encoding method for encoding a stereo signal by a bit stream signal by complex prediction stereo coding, the method comprising the steps of:
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determining a complex prediction coefficient; transforming the stereo signal into a first frequency-domain representation of a downmix channel and a residual channel, in a relationship determined by the complex prediction coefficient, the first frequency-domain representation comprising first spectral components representing spectral content of the corresponding signal expressed in a first subspace of a multidimensional space; and encoding the downmix and residual channels and the complex prediction coefficient as said bit stream signal, the downmix and residual channels being segmented into time frames, said method further comprising; selecting, for each time segment, whether to encode the stereo signal in this time segment by at least one of the following options; direct stereo coding, joint stereo coding, and complex-prediction stereo coding, wherein, if direct stereo coding is selected, the stereo signal is transformed into a frequency-domain representation of a left channel and a right channel, which are encoded as said bit stream signal; and wherein, if joint stereo coding is selected, the stereo signal is transformed into a frequency-domain representation of a downmix and side channel, which are encoded as said bit stream signal. - View Dependent Claims (25, 26, 27, 28, 30)
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Specification