Apparatus and a method for decoding an encoded audio signal

An apparatus for encoding an audio signal comprising:

• a first encoder which is configured to encode in accordance with a first encoding algorithm, the first encoding algorithm comprising a first frequency bandwidth, wherein the first encoder comprises an LPC-based coder;
• a second encoder which is configured to encode in accordance with a second encoding algorithm, the second encoding algorithm comprising a second frequency bandwidth being smaller than the first frequency bandwidth, wherein the second encoder comprises a transform-based coder;
• a decision stage for indicating the first encoding algorithm for a first portion of the audio signal and for indicating the second encoding algorithm for a second portion of the audio signal, the second portion being different from the first portion;
• and
• a bandwidth extension module for calculating BWE parameters for the audio signal, wherein the BWE module is configured to be controlled by the decision stage to calculate the BWE parameters for a band not comprising the first frequency bandwidth in the first portion of the audio signal and for a band not comprising the second frequency bandwidth in the second portion of the audio signal,
• wherein the first or the second frequency bandwidth is defined by a variable crossover frequency and wherein the decision stage is configured to output the variable crossover frequency,
• wherein the BWE module is configured to use a first crossover frequency for calculating the BWE parameters for a signal encoded using the first encoder and to use a second crossover frequency for a signal encoded using the second encoder, wherein the first crossover frequency is higher than the second crossover frequency.

A method for decoding an encoded audio signal, the encoded audio signal comprising a first portion encoded in accordance with a first encoding algorithm, a second portion encoded in accordance with a second encoding algorithm, BWE parameters for the first portion and the second portion and a coding mode information indicating a first decoding algorithm or a second decoding algorithm, the method comprising:

• decoding the first portion in accordance with the first decoding algorithm for a first time portion of the encoded signal to acquire a first decoded signal, wherein decoding the first portion comprises using an LPC-based coder;
• decoding the second portion in accordance with the second decoding algorithm for a second time portion of the encoded signal to acquire a second decoded signal, wherein decoding the second portion comprises using a transform-based coder;
• performing a bandwidth extension algorithm by a BWE module comprising a controllable crossover frequency, using the first decoded signal and the BWE parameters for the first portion, and performing, by the BWE module comprising the controllable crossover frequency, a bandwidth extension algorithm using the second decoded signal and the bandwidth extension parameter for the second portion,
• wherein a first crossover frequency is used for the bandwidth extension for the first decoded signal and a second crossover frequency is used for the bandwidth extension for the second decoded signal, wherein the first crossover frequency is higher than the second crossover frequency;
• and
• controlling the crossover frequency for the BWE module in accordance with the coding mode information.

A method for encoding an audio signal comprising:

• encoding in accordance with a first encoding algorithm, the first encoding algorithm comprising a first frequency bandwidth, wherein encoding in accordance with a first encoding algorithm comprises using an LPC-based coder;
• encoding in accordance with a second encoding algorithm, the second encoding algorithm comprising a second frequency bandwidth being smaller than the first frequency bandwidth, wherein encoding in accordance with a second encoding algorithm comprises using a transform-based coder;
• indicating the first encoding algorithm for a first portion of the audio signal and the second encoding algorithm for a second portion of the audio signal, the second portion being different from the first portion;
• and
• calculating BWE parameters for the audio signal such that the BWE parameters are calculated for a band not comprising the first frequency bandwidth in the first portion of the audio signal and for a band not comprising the second frequency bandwidth in the second portion of the audio signal,
• wherein the first or the second frequency bandwidth is defined by a variable crossover frequency,
• wherein the BWE module is configured to use a first crossover frequency for calculating the BWE parameters for a signal encoded using the LPC-based coder and to use a second crossover frequency for a signal encoded using the transform-based coder, wherein the first crossover frequency is higher than the second crossover frequency.

A non-transitory storage medium having stored thereon a computer program for performing, when running on a computer, the method for encoding an audio signal, said method comprising:

• encoding in accordance with a first encoding algorithm, the first encoding algorithm comprising a first frequency bandwidth, wherein encoding in accordance with a first encoding algorithm comprises using an LPC-based coder;
• encoding in accordance with a second encoding algorithm, the second encoding algorithm comprising a second frequency bandwidth being smaller than the first frequency bandwidth, wherein encoding in accordance with a second encoding algorithm comprises using a transform-based coder;
• indicating the first encoding algorithm for a first portion of the audio signal and the second encoding algorithm for a second portion of the audio signal, the second portion being different from the first portion;
• and
• calculating BWE parameters for the audio signal such that the BWE parameters are calculated for a band not comprising the first frequency bandwidth in the first portion of the audio signal and for a band not comprising the second frequency bandwidth in the second portion of the audio signal,
• wherein the first or the second frequency bandwidth is defined by a variable crossover frequency,
• wherein the BWE module is configured to use a first crossover frequency for calculating the BWE parameters for a signal encoded using the LPC-based coder and to use a second crossover frequency for a signal encoded using the transform-based coder, wherein the first crossover frequency is higher than the second crossover frequency.