Methods for parametric multi-channel encoding
The present document relates to audio coding systems. In particular, the present document relates to efficient methods and systems for parametric multi-channel audio coding. An audio encoding system configured to generate a bitstream indicative of a downmix signal and spatial metadata for generating a multi-channel upmix signal from the downmix signal is described. The system comprises a downmix processing unit configured to generate the downmix signal from a multi-channel input signal; wherein the downmix signal comprises m channels and wherein the multi-channel input signal comprises n channels; n, m being integers with m<n. Furthermore, the system comprises a parameter processing unit configured to determine the spatial metadata from the multi-channel input signal. In addition, the system comprises a configuration unit configured to determine one or more control settings for the parameter processing unit based on one or more external settings; wherein the one or more external settings comprise a target data-rate for the bitstream and wherein the one or more control settings comprise a maximum data-rate for the spatial metadata.
1. A method comprising:
receiving, by an audio processor, a multi-channel input audio signal;
determining a first set of dynamic range control (DRC) values configured for controlling a dynamic range of an output audio signal;
determining a second set of DRC values configured for preventing the multi-channel input audio signal from clipping during downmixing by the audio processor;
applying the second set of DRC values to the multi-channel input audio signal to obtain an attenuated multi-channel input audio signal;
downmixing the attenuated multi-channel input audio signal to obtain a downmix signal; and
generating the output audio signal from the first set of DRC values and the downmix audio signal.
2. An apparatus comprising:
one or more processors;
memory storing instructions, which, when executed by the one or more processors, causes the one or more processors to perform operations comprising:
receiving a multi-channel input audio signal;
determining a first set of dynamic range control (DRC) values configured for controlling a dynamic range of an output audio signal;
determining a second set of DRC values configured for preventing the multi-channel input audio signal from clipping during downmixing by the apparatus;
applying the second set of DRC values to the multi-channel input audio signal to obtain an attenuated multi-channel input audio signal;
downmixing the attenuated multi-channel input audio signal to obtain a downmix signal; and
generating the output audio signal from the first set of DRC values and the downmix audio signal.
3. The apparatus of claim 2 , wherein generating the output audio signal comprises applying the first set of DRC values to the downmix audio signal.
4. The apparatus of claim 2 , wherein the first and/or second sets of DRC values are represented in logarithmic form as dB values.
5. The apparatus of claim 2 , wherein the multi-channel input audio signal is divided into a sequence of frames of samples of the multi-channel audio signal, and determining the first and/or second sets of DRC values comprises determining a DRC value for each sample of each frame of the sequence of frames.
6. The apparatus of claim 5 , wherein determining a DRC value for each sample of a frame comprises interpolating between a DRC value of the frame and a DRC value of a preceding frame.
7. The method of claim 6 , wherein the interpolation is a spline interpolation.
8. The apparatus of claim 2 , wherein the downmix signal is a stereo signal.
9. The apparatus of claim 2 , wherein the left and right channels of the downmix are generated based on different linear combinations of channels of the multi-channel input audio signal.
10. A non-transitory computer readable storage medium comprising a sequence of instructions which, when performed by an audio signal processing device cause the audio signal processing device to perform a method comprising:
receiving, by an audio processor, a multi-channel input audio signal;
determining a first set of dynamic range control (DRC) values configured for controlling a dynamic range of an output audio signal;
determining a second set of DRC values configured for preventing the multi-channel input audio signal from clipping during downmixing by the audio processor;
applying the second set of DRC values to the multi-channel input audio signal to obtain an attenuated multi-channel input audio signal;
downmixing the attenuated multi-channel input audio signal to obtain a downmix signal; and
generating the output audio signal from the first set of DRC values and the downmix audio signal.