Device and method for postprocessing a decoded multi-channel audio signal or a decoded stereo signal

1. A device for post-processing at least one channel signal of a plurality of channel signals of a multi-channel signal, the at least one channel signal being generated from a decoded downmix signal by a low-bit-rate audio coding/decoding system, the device comprising:

a receiver for receiving the at least one channel signal generated from the decoded downmix signal, a time envelope of the decoded down mix signal, an interchannel time difference between the at least one channel signal and the downmix signal, and a classification indication indicating a transient type of the downmix signal;

a post-processor for post-processing the at least one channel signal based on the time envelope of the decoded downmix signal weighted by a respective weighting factor and in dependence on the classification indication and the interchannel time difference, wherein the respective weighting factor depends on a received channel level difference, CLDm, between the at least one channel signal and a reference signal; and

a decider adapted to decide dependent on the classification indication indicating a transient type of the downmix signal and on a further classification indication indicating a transient type of the channel signal, whether the at least one of the plurality of channel signals is post-processed, and to decide dependent on the interchannel time difference, whether the at least one channel signal is post-processed by a delayed time envelope of the downmix signal weighted by the respective weighting factor.

2. The device of claim 1 , wherein the receiver is adapted to receive the plurality of channel signals and a plurality of interchannel time differences, wherein each of the interchannel time differences is associated to a channel signal of the plurality of channel signals and comprises information about a time difference between the respective channel signal and the downmix signal; and

wherein the decider is adapted to control the post-processor.

3. The device of claim 1 , wherein the decider is configured to control the post-processor to post-process the at least one channel signal using a delayed time envelope of the downmix signal weighted by the respective weighting factor in case the classification indication indicates that the downmix signal is downmix transient and the further classification indication associated to the at least one multi-channel signal indicates that the at least one channel is not channel transient, and the channel specific interchannel time difference associated to the at least one multi-channel signal indicates that the at least one channel signal is delayed with regard to the downmix signal.

4. The device of claim 1 , wherein the decider is configured to control the post-processor to not post-process the at least one channel signal in case the classification indication indicates that the downmix signal is downmix transient and the further classification indication associated to the at least one multi-channel signal indicates that the at least one channel is channel transient.

5. The device of claim 1 , wherein the classification indication indicates that a channel is channel transient in case a change over time of a relation between an energy of the channel signal and an energy of a reference signal exceeds a predetermined threshold.

6. The device of claim 5 , wherein the downmix signal forms the reference signal.

7. The device of claim 1 , wherein the classification indicates that the downmix signal is downmix transient in case a change over time of an energy of the downmix signal exceeds a predetermined threshold.

8. The device of claim 1 , wherein the decider is adapted for deciding based on the interchannel time difference, whether the at least one channel signal is delayed with regard to the downmix signal, and, if the at least one channel signal is delayed with regard to the downmix signal, to delay the time envelope of the downmix signal to obtain a delayed time envelope for post-processing the delayed channel signal, wherein the decider is adapted to delay the time envelope of the downmix signal by the interchannel time difference.

9. A decoder for parametric multi-channel audio decoding, the decoder comprising a downmix decoder, an upmixer and a device comprising:

a receiver for receiving at least one channel signal generated from a decoded downmix signal by the decoder, a time envelope of the decoded downmix signal, an interchannel time difference between the at least one channel signal and the downmix signal, and a classification indication indicating a transient type of the downmix signal;

a post-processor for post-processing the at least one channel signal based on the time envelope of the decoded downmix signal weighted by a respective weighting factor and in dependence on the classification indication and the interchannel time difference, wherein the respective weighting factor depends on a received channel level difference, CLDm, between the at least one channel signal and a reference signal, and wherein the downmix decoder is configured to receive an encoded downmix signal representing the multi-channel signal and to decode the encoded downmix signal to generate the decoded downmix signal, wherein the upmixer is configured to receive the decoded downmix signal from the downmix decoder and multi-channel parameters associated to the downmix signal and to upmix the decoded downmix signal based on the multi-channel parameters to generate the plurality of channel signals of the multi-channel signal; and

a decider adapted to decide dependent on the classification indication indicating a transient type of the downmix signal and on a further classification indication indicating a transient type of the channel signal, whether the at least one channel signal is post-processed, and to decide dependent on the interchannel time difference, whether the at least one channel signal is post-processed by a delayed time envelope of the downmix signal weighted by the respective weighting factor.

10. A method for post-processing at least one channel signal of a plurality of channel signals of a multi-channel signal, the at least one channel signal being generated from a decoded downmix signal by a low-bit-rate audio coding/decoding system, the method comprising the following steps:

receiving the at least one channel signal generated from the decoded downmix signal, a time envelope of the decoded downmix signal, an interchannel time difference between the at least one channel signal and the downmix signal, and a classification indication indicating a transient type of the downmix signal;

deciding dependent on the classification indication indicating a transient type of the downmix signal and on a further classification indication indicating a transient type of the channel signal, which one or ones of the plurality of channel signals are post-processed, and deciding dependent on the interchannel time difference, whether the at least one channel signal is post-processed by a delayed time envelope of the downmix signal weighted by a respective weighting factor; and

post-processing the at least one channel signal based on the time envelope of the decoded downmix signal weighted by the respective weighting factor and in dependence on the classification indication and the interchannel time difference, wherein the respective weighting factor depends on a received channel level difference, CLDm, between the at least one channel signal and a reference signal.

11. A device for post-processing at least one of a left or a right channel signal of a stereo signal, the left and the right channel signals being generated from a decoded downmix signal by a low-bit-rate coding/decoding system, the device comprising:

a receiver for receiving the left channel signal and the right channel signal generated from the decoded downmix signal, a time envelope of the decoded downmix signal, an interchannel time difference between the left channel signal and the right channel signal of the stereo signal and a classification indication indicating a transient type of the downmix signal or of the stereo signal,

a post-processor for post-processing at least one of the left or right channel signals based on the time envelope of the decoded downmix signal weighted by a respective weighting factor and in dependence on the interchannel time difference and on the classification indication, wherein the respective weighting factor depends on a received channel level difference, CLD, of the left and the right channel of the stereo signal, and

a decider adapted to decide dependent on the classification indication indicating a transient type of the downmix signal and on a further classification indication indicating a transient type of the stereo signal, which one or ones of the channel signals are post-processed, and to decide dependent on the interchannel time difference, whether the left or right channel signal is post-processed by a delayed time envelope of the downmix signal weighted by the respective weighting factor.

12. The device of claim 11 , wherein the decider is adapted to decide based on the interchannel time difference, whether one of the left channel signal and the right channel signal of the stereo signal is delayed with regard to the other channel signal, and, if one of the left channel signal or the right channel signal of the stereo signal is delayed with regard to the other channel signal, to post-process the delayed channel signal of the stereo signal using the delayed time envelope of the decoded downmix signal weighted by the respective weighting factor, and to post-process the other not delayed channel signal using the time envelope of the decoded downmix signal weighted by a respective weighting factor.

13. A method for post-processing at least one of a left or a right channel signal of a stereo signal, the left and the right channel signal generated from a decoded downmix signal by a low-bit-rate coding/decoding system, the method comprising:

receiving the left channel signal and the right channel signal generated from the decoded downmix signal, a time envelope of the decoded downmix signal, an interchannel time difference between the left channel signal and the right channel signal of the stereo signal and a classification indication indicating a transient type of the downmix signal or of the stereo signal;

deciding dependent on the classification indication indicating a transient type of the downmix signal and on a further classification indication indicating a transient type of the stereo signal, which one or ones of the channel signals are post-processed, and deciding dependent on the interchannel time difference, whether the left or right channel signal is post-processed by a delayed time envelope of the downmix signal weighted by a respective weighting factor; and

post-processing at least one of the left or right channel signals based on the time envelope of the decoded downmix signal weighted by the respective weighting factor and in dependence on the interchannel time difference and on the classification indication, wherein the respective weighting factor depends on a received channel level difference, CLD, of the left and the right channel of the stereo signal.