Low bitrate audio encoding/decoding scheme having cascaded switches
An audio encoder has a first information sink oriented encoding branch such as a spectral domain encoding branch, a second information source or SNR oriented encoding branch such as an LPC-domain encoding branch, and a switch for switching between the first and second encoding branches, the second encoding branch having a converter into a specific domain different from the spectral domain such as an LPC analysis stage generating an excitation signal, and the second encoding branch having a specific domain coding branch such as LPC domain processing branch, and a specific spectral domain coding branch such as LPC spectral domain processing branch, and an additional switch for switching between the specific domain coding branch and the specific spectral domain coding branch. An audio decoder has a first domain decoder, a second domain decoder, and a third domain decoder as well as two cascaded switches for switching between the decoders.
1. A decoding device for decoding an encoded audio signal, the encoded audio signal comprising a first encoded signal, a first processed signal in a second domain, and a second processed signal in a third domain, wherein the first encoded signal, the first processed signal, and the second processed signal are related to different time portions of a decoded audio signal, and wherein a first domain, the second domain and the third domain are different from each other, comprising:
a first decoding branch for decoding the first encoded signal to obtain a first decoded signal;
a second decoding branch for decoding the first processed signal or the second processed signal,
wherein the second decoding branch comprises
a first inverse processing branch for inverse processing the first processed signal in the second domain to acquire a first inverse processed signal in the second domain;
a second inverse processing branch for inverse processing the second processed signal in the third domain to acquire a second inverse processed signal in the second domain;
a first combiner for combining the first inverse processed signal in the second domain and the second inverse processed signal in the second domain to acquire a combined signal in the second domain; and
a converter for converting the combined signal in the second domain to the first domain to obtain a converted signal in the first domain; and
a second combiner for combining the converted signal in the first domain and the first decoded signal obtained by the first decoding branch to acquire the decoded audio signal in the first domain,
wherein the first decoding branch and the second decoding branch are operative to operate in a block wise manner, wherein a switching over action in the first combiner or the second combiner takes place, at the minimum, after a block of a predefined number of samples of a signal, the predefined number of samples forming a frame length for the corresponding combiner, and
wherein a size of the frame length for the second combiner is greater than the size of the frame length of the first combiner.
2. The decoding device of claim 1 , in which the first combiner or the second combiner comprises a switch comprising a cross fading functionality.
3. The decoding device of claim 1 , in which the first domain is a time domain, the second domain is an LPC domain, the third domain is an LPC spectral domain, or the first encoded signal is encoded in a fourth domain, which is a time-spectral domain acquired by time/frequency converting a signal in the first domain.
4. The decoding device of claim 1 , in which the first decoding branch comprises an inverse coder and a de-quantizer and a frequency domain time domain converter, or
the second decoding branch comprises an inverse coder and a de-quantizer in the first inverse processing branch or an inverse coder and a de-quantizer and an LPC spectral domain to LPC domain converter in the second inverse processing branch.
5. The decoding device of claim 4 , in which the first decoding branch or the second inverse processing branch comprises an overlap-adder for performing a time domain aliasing cancellation functionality.
6. The decoding device of claim 1 , in which the first decoding branch or the second inverse processing branch comprises a de-warper controlled by a warping characteristic comprised in the encoded audio signal.
7. The decoding device of claim 1 , in which the encoded signal comprises, as side information, an indication whether the encoded audio signal is one of the first encoded signal, the first processed signal in the second domain, and the second processed signal in a third domain, and
which further comprises a parser for parsing the encoded audio signal to determine, based on the side information, whether the encoded audio signal in a respective time portion of the encoded audio signal is the first encoded signal to be processed by the first decoding branch, or is the first processed signal to be processed by the first inverse processing branch of the second decoding branch, or is the second processed signal to be processed by the second inverse processing branch of the second decoding branch.
8. Method of decoding an encoded audio signal, the encoded audio signal comprising a first encoded signal, a first processed signal in a second domain, and a second processed signal in a third domain, wherein the first encoded signal, the first processed signal, and the second processed signal are related to different time portions of a decoded audio signal, and wherein a first domain, the second domain and the third domain are different from each other, the method comprising:
first decoding the first encoded signal to obtain a first decoded signal;
second decoding the first processed signal or the second processed signal,
wherein the second decoding comprises:
inverse processing the first processed signal in the second domain to acquire a first inverse processed signal in the second domain;
inverse processing the second processed signal in the third domain to acquire a second inverse processed signal in the second domain;
first combining the first inverse processed signal in the second domain and the second inverse processed signal in the second domain to acquire a combined signal in the second domain; and
converting the combined signal in the second domain to the first domain to obtain a converted signal in the first domain; and
second combining the converted signal in the first domain and the first decoded signal to acquire the decoded audio signal in the first domain,
wherein the first decoding and the second decoding are operative to operate in a block wise manner, wherein a switching over action in the first combining or the second combining takes place, at the minimum, after a block of a predefined number of samples of a signal, the predefined number of samples forming a frame length for the corresponding combining, and
wherein a size of the frame length for the second combining is greater than the size of the frame length of the first combining.
9. Non-transitory storage medium having stored thereon a computer program for performing, when running on a computer, a method of decoding an encoded audio signal, the encoded audio signal comprising a first encoded signal, a first processed signal in a second domain, and a second processed signal in a third domain, wherein the first encoded signal, the first processed signal, and the second processed signal are related to different time portions of a decoded audio signal, and wherein a first domain, the second domain and the third domain are different from each other, the method comprising:
first decoding the first encoded signal to obtain a first decoded signal;
second decoding the first processed signal or the second processed signal,
wherein the second decoding comprises:
inverse processing the first processed signal in the second domain to acquire a first inverse processed signal in the second domain;
inverse processing the second processed signal in the third domain to acquire a second inverse processed signal in the second domain;
first combining the first inverse processed signal in the second domain and the second inverse processed signal in the second domain to acquire a combined signal in the second domain; and
converting the combined signal in the second domain to the first domain to obtain a converted signal in the first domain; and
second combining the converted signal in the first domain and the first decoded signal to acquire the decoded audio signal in the first domain,
wherein the first decoding and the second decoding are operative to operate in a block wise manner, wherein a switching over action in the first combining or the second combining takes place, at the minimum, after a block of a predefined number of samples of a signal, the predefined number of samples forming a frame length for the corresponding combining, and
wherein a size of the frame length for the second combining is greater than the size of the frame length of the first combining.