AUDIO UP-MIXING DEVICE WITH THE CAPABILITY OF OPERATION IN PREDICTIVE OR NON-PREDICTIVE MODE

Claims

1. A decoder system for providing a stereo signal by complex prediction stereo coding, the decoder system comprising: an upmix stage adapted to generate a stereophonic signal based on first frequency domain representations of the downmix signal and the residual signal, where each of the first frequency domain representations comprises first spectral components that represent the spectral composition of the corresponding signal expressed in a first subspace of a multidimensional space, where the upmix stage comprises: a module for calculating a second frequency domain representation of a downmix signal based on its first frequency domain representation, wherein the second frequency domain representation comprises second spectral components representing the spectral composition of the signal expressed in a second subspace of a multidimensional space that comprises a portion of the multidimensional space not included in the first subspace; wherein the module is adapted to determine the second spectral components of the downmix signal by applying a finite impulse response (FIR) filter to the first spectral components of the downmix signal; a weighted adder configured to calculate a side signal based on 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 the bitstream signal received by the decoder system; and a sum-difference stage designed to calculate a stereo signal based on a first representation of the downmix signal in the frequency domain and a side signal; a first modifier stage in the frequency domain, located upstream of the upmix stage and capable of operating in an active mode, in which it processes the frequency domain representation of at least one signal, and in a passive mode, in which it acts as a repeater; and a second modifier stage in the frequency domain, located downstream of the upmix stage and capable of operating in an active mode, in which it processes the frequency domain representation of at least one signal, and in a passive mode, in which it plays the role of a repeater.

2. The decoder system according to claim 1, characterized in that the impulse response of the FIR filter is determined depending on a window function applied to determine the first representation of the downmix signal in the frequency domain.

3. The decoder system according to claim 1, characterized in that at least one of the said stages of the first and second modifier in the frequency domain is a stage of temporary noise shaping, TNS.

4. The decoder system according to claim 3, characterized in that it is also adapted to receive for each time frame a data field associated with this frame and to act, in response to the value of the data field, a first modifier stage in the frequency domain in its active mode or in its relay mode and to act a second modifier stage in the frequency domain in its active mode or in its relay mode.

5. The decoder system according to item 1, characterized in that it additionally contains: a dequantization stage located upstream of the upmix stage for providing said first frequency domain representations of the downmix signal and the residual signal based on the bitstream signal.

6. The decoder system according to item 1, characterized in that the first spectral components have real values expressed in the first subspace; the second spectral components have imaginary values expressed in the second subspace; optionally, the first spectral components are obtained using one of the following: discrete cosine transform (DCT) or modified discrete cosine transform, MDCT, and optionally, the second spectral components are obtained using one of the following: discrete sine transform, DST, or modified discrete sine transform, MDST.

7. The decoder system according to item 6, characterized in that: the downmix signal is divided into successive time frames, each of which is associated with a value of the complex prediction coefficient; and a module for calculating a second frequency domain representation of a downmix signal is adapted to self-switch off in response to the fact that the absolute value of the imaginary part of the complex prediction coefficient is less than a predetermined tolerance for a time frame, and thus it does not generate an output signal for this time frame.

8. The decoder system according to claim 5, characterized in that said stereophonic signal is represented in the time domain, and the decoder system also comprises: a switching unit located between said dequantization stage and said upmix stage, configured to function as: (a) a relay stage or (b) sum-difference stage, thereby providing the ability to switch between directly and jointly encoded input stereo signals; an inverse transform stage adapted to compute a time-domain representation of the stereo signal; and a selector circuit located upstream of the inverse conversion stage, adapted for its selective connection either to: (a) a point downstream of the upmix stage whereby the complex predicted stereo signal is fed to the inverse transform stage, or (b) a point downstream of the switching node and upstream of the upmix stage, whereby the stereo signal obtained by direct stereo encoding is fed to the inverse conversion stage.

9. The decoder system according to claim 5, characterized in that the module intended for calculating the second representation of the downmix signal in the frequency domain comprises: an inverse transform stage configured to compute a time domain representation of the downmix signal and / or the side signal based on a first frequency domain representation of the corresponding signal in a first subspace of the multidimensional space; and a transformation stage designed to calculate a second representation of the corresponding signal in the frequency domain based on the representation of this signal in the time domain, wherein preferably the inverse transform stage performs a modified discrete cosine transform, MDCT, and the transform stage performs a modified discrete sine transform, MDST.

10. The decoder system according to claim 9, characterized in that said stereophonic signal is represented in the time domain, and the decoder system also comprises: a switching unit located between said dequantization stage and said upmix stage, configured to function as: (a) a relay stage for use in joint stereo coding; or (b) sum-difference stage for use in direct stereo coding; an additional inverse transform stage located at the upmix stage, designed to calculate the time domain representation of the side signal; a selector circuit located upstream of the inverse conversion stages, adapted for their selective connection either with: (a) an additional sum-difference stage which in turn is associated with a point downstream of the switching node and upstream of the upmix stage; or (b) a downmix signal obtained from the switching node and a sideband signal obtained from the weighted adder.

11. A decoding method for upmixing an input stereo signal by complex prediction stereo coding into an output stereo signal, wherein: said input stereo signal comprises first frequency domain representations of a downmix channel and a residual channel and a complex prediction coefficient; and each of the said first frequency domain representations contains first spectral components that represent the spectral composition of the corresponding channel expressed in the first subspace of the multidimensional space, wherein the method is carried out by an upmixing stage and includes the following steps: calculating a second frequency domain representation of a downmix channel based on its first frequency domain representation, wherein the second frequency domain representation comprises second spectral components representing the spectral composition of the channel expressed in a second subspace of a multidimensional space that comprises a portion of the multidimensional space not included in the first subspace, wherein calculating the second frequency domain representation of the downmix channel includes determining the second spectral components of the downmix channel by applying a finite impulse response (FIR) filter to the first spectral components of the downmix channel; calculating a side channel based on the first and second frequency domain representations of the downmix channel, the first frequency domain representation of the residual channel, and the complex prediction coefficient, and also includes or is performed before the upmixing step of applying temporal noise shaping, TNS, to said first frequency domain representation of the downmix channel and / or said first frequency domain representation of the residual channel; or a step of applying TNS to at least one channel of said output stereo signal, performed after the upmixing step.

12. A computer program product containing a machine-readable medium in which commands are stored that, when executed by a general-purpose computer, perform the method according to paragraph 11.