Apparatus and method for generating a multi-channel output signal
View Patent ↗An apparatus for generating a multi-channel output signal performs a center channel cancellation to obtain improved base channels for reconstructing left-side output channels or right-side output channels. In particular, the apparatus includes a cancellation channel calculator for calculating a cancellation channel using information related to the original center channel available at the decoder. The device furthermore includes a combiner for combining a transmission channel with the cancellation channel. Finally, the apparatus includes a reconstructor for generating the multi-channel output signal. Due to the center channel cancellation, the channel reconstructor not only uses a different base channel for reconstructing the center channel but also uses base channels different from the transmission channels for reconstructing left and right output channels which have a reduced or even completely cancelled influence of the original center channel.
1. Apparatus for generating a multi-channel output signal having K output channels, the multi-channel output signal corresponding to a multi-channel input signal having C input channels, using E transmission channels, the E transmission channels representing a result of a downmix operation having C input channels as an input, and using parametric information related to the input channels, wherein E is ≧2, C is >E, and K is >1 and ≦C, and wherein the downmix operation is effective to introduce a first input channel in a first transmission channel and in a second transmission channel, and to additionally introduce a second input channel in the first transmission channel, comprising:
a cancellation channel calculator for calculating a cancellation channel using information related to the first input channel included in the first transmission channel, the second transmission channel or the parametric information;
a combiner for combining the cancellation channel and the first transmission channel or a processed version thereof to obtain a second base channel, in which an influence of the first input channel is reduced compared to the influence of the first input channel on the first transmission channel; and
a channel reconstructor for reconstructing a second output channel corresponding to the second input channel using the second base channel and parametric information related to the second input channel, and for reconstructing a first output channel corresponding to the first input channel using a first base channel being different from the second base channel in that the influence of the first channel is higher compared to the second base channel, and parametric information related to the first input channel.
2. Apparatus in accordance with claim 1 , in which the combiner is operative to subtract the cancellation channel from the first transmission channel or the processed version thereof.
3. Apparatus in accordance with claim 1 , in which the cancellation channel calculator is operative to calculate an estimate for the first input channel using the first transmission channel and the second transmission channel to obtain the cancellation channel.
4. Apparatus in accordance with claim 1 , in which the parametric information includes a difference parameter between the first input channel and a reference channel, and in which the cancellation channel calculator is operative to calculate a sum of the first transmission channel and the second transmission channel and to weight the sum using the difference parameter.
5. Apparatus in accordance with claim 1 , in which the downmix operation is such that the first input channel is introduced into the first transmission channel after being scaled by a downmix factor, and in which the cancellation channel calculator is operative to scale the sum of the first and the second transmission channels using a scaling factor, which depends on the downmix factor.
6. Apparatus in accordance with claim 5 , in which the weighting factor is equal to the downmix factor.
7. Apparatus in accordance with claim 1 , in which the cancellation channel calculator is operative to determine a sum of the first and the second transmission channels to obtain the first base channel.
8. Apparatus in accordance with claim 1 , further comprising a processor which is operative to process the first transmission channel by weighting using a first weighting factor, and in which the cancellation channel calculator is operative to weight the second transmission channel using a second weighting factor.
9. Apparatus in accordance with claim 8 , in which the parametric information includes the difference parameter between the first input channel and a reference channel, and in which the cancellation channel calculator is operative to determine the second weighting factor based on a difference parameter.
10. Apparatus in accordance with claim 8 , in which the first weighting factor is equal to (1−h), wherein h is a real value, and in which the second weighting factor is equal to h.
11. Apparatus in accordance with claim 10 , in which the parametric information includes a level difference value, and wherein h is derived from the parametric level difference value.
12. Apparatus in accordance with claim 11 , in which h is equal to a value derived from the level difference divided by a factor depending on the downmix operation.
13. Apparatus in accordance with claim 10 , in which the parametric information includes the level difference between the first channel and the reference channel, and in which h is equal to 1√2×10 L/20 , wherein L is the level difference.
14. Apparatus in accordance with claim 1 , in which the parametric information further includes a control signal dependent on the relation between the first input channel and the second input channel, and
in which the cancellation channel calculator is controlled by the control signal to actively increase or decrease an energy of the cancellation channel or even disable the cancellation channel calculation at all.
15. Apparatus in accordance with claim 1 , in which the downmix operation is further operative to introduce a third input channel into the second transmission channel, the apparatus further comprising a further combiner for combining the cancellation channel and the second transmission channel or a processed version thereof to obtain a third base channel, in which an influence of the first input channel is reduced compared to the influence of the first input channel on the second transmission channel; and
a channel reconstructor for reconstructing the third output channel corresponding to the third input channel using the third base channel and parametric information related to the third input channel.
16. Apparatus in accordance with claim 1 , in which the parametric information includes inter-channel level differences, inter-channel time differences, inter-channel phase differences or inter-channel correlation values, and
in which the channel reconstructor is operative to apply any one of the parameters of the above group on a base channel to obtain a raw output channel.
17. Apparatus in accordance with claim 16 , in which the channel reconstructor is operative to scale the raw output channel so that the total energy in the final reconstructed output channel is equal to the total energy of the E transmission channels.
18. Apparatus in accordance with claim 1 , in which the parametric information is given band wise, and in which the cancellation channel calculator, the combiner and the channel reconstructor are operative to process the plurality of bands using band wise-given parametric information, and
in which the apparatus further comprises a time/frequency conversion unit for converting the transmission channels into a frequency representation having frequency bands, and a frequency/time conversion unit for converting reconstructed frequency bands into the time domain.
19. The apparatus of claim 1 further comprising:
a system selected from the group consisting of a digital video player, a digital audio player, a computer, a satellite receiver, a cable receiver, a terrestrial broadcast receiver, and a home entertainment system; and
wherein the system comprises the channel calculator, the combiner, and the channel reconstructor.
20. Method of generating a multi-channel output signal having K output channels, the multi-channel output signal corresponding to a multi-channel input signal having C input channels, using E transmission channels, the E transmission channels representing a result of a downmix operation having C input channels as an input, and using parametric information related to the input channels, wherein E is ≧2, C is >E, and K is >1 and ≦C, and wherein the downmix operation is effective to introduce a first input channel in a first transmission channel and in a second transmission channel, and to additionally introduce a second input channel in the first transmission channel, comprising:
calculating a cancellation channel using information related to the first input channel included in the first transmission channel, the second transmission channel or the parametric information;
combining the cancellation channel and the first transmission channel or a processed version thereof to obtain a second base channel, in which an influence of the first input channel is reduced compared to the influence of the first input channel on the first transmission channel; and
reconstructing a second output channel corresponding to the second input channel using the second base channel and parametric information related to the second input channel, and a first output channel corresponding to the first input channel using a first base channel being different from the second base channel in that the influence of the first channel is higher compared to the second base channel, and parametric information related to the first input channel.
21. Computer program having a program code for implementing, when running on a computer, a method for generating a multi-channel output signal having K output channels, the multi-channel output signal corresponding to a multi-channel input signal having C input channels, using E transmission channels, the E transmission channels representing a result of a downmix operation having C input channels as an input, and using parametric information related to the input channels, wherein E is ≧2, C is >E, and K is >1 and ≦C, and wherein the downmix operation is effective to introduce a first input channel in a first transmission channel and in a second transmission channel, and to additionally introduce a second input channel in the first transmission channel, the method comprising:
calculating a cancellation channel using information related to the first input channel included in the first transmission channel, the second transmission channel or the parametric information;
combining the cancellation channel and the first transmission channel or a processed version thereof to obtain a second base channel, in which an influence of the first input channel is reduced compared to the influence of the first input channel on the first transmission channel; and
reconstructing a second output channel corresponding to the second input channel using the second base channel and parametric information related to the second input channel, and a first output channel corresponding to the first input channel using a first base channel being different from the second base channel in that the influence of the first channel is higher compared to the second base channel, and parametric information related to the first input channel.