Apparatus and a Method for Decoding an Encoded Audio Signal

• US 20110202353A1
• Filed: 01/11/2011
• Published: 08/18/2011
• Est. Priority Date: 07/11/2008
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Nagel, Frederick, Neuendorf, Max, Popp, Harald, Grill, Bernhard, Multrus, Markus, Kraemer, Ulrich, Gayer, Marc, Lohwasser, Markus, Rettelbach, Nikolaus, Bacigalupo, Virgilio, Jander, Manuel
• Granted Patent: US 8,275,626 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding
• CPC Class Codes: G10L 21/038 using band spreading techniques
• CPC Class Codes: G10L 21/04 Time compression or expansion

Abstract

An apparatus for decoding an encoded audio signal having first and second portions encoded in accordance with first and second encoding algorithms, respectively, BWE parameters for the first and second portions and a coding mode information indicating a first or a second decoding algorithm, includes first and second decoders, a BWE module and a controller. The decoders decode portions in accordance with decoding algorithms for time portions of the encoded signal to obtain decoded signals. The BWE module has a controllable crossover frequency and is configured for performing a bandwidth extension algorithm using the first decoded signal and the BWE parameters for the first portion, and for performing a bandwidth extension algorithm using the second decoded signal and the bandwidth extension parameter for the second portion. The controller controls the crossover frequency for the BWE module in accordance with the coding mode information.

Claims

1. An apparatus 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, comprising:

a first decoder for 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 the first decoder comprises an LPC-based coder;

a second decoder for 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 the second decoder comprises a transform-based coder;

a BWE module comprising a controllable crossover frequency, the BWE module being configured for performing a bandwidth extension algorithm using the first decoded signal and the BWE parameters for the first portion, and for performing a bandwidth extension algorithm using the second decoded signal and the bandwidth extension parameter for the second portion,

wherein the BWE module is configured to use a first crossover frequency for the bandwidth extension for the first decoded signal and to use a second crossover frequency for the bandwidth extension for the second decoded signal, wherein the first crossover frequency is higher than the second crossover frequency; and

a controller for controlling the crossover frequency for the BWE module in accordance with the coding mode information.

2. The apparatus for decoding of claim 1, further comprising an input interface for inputting the encoded audio signal as a bitstream.

3. The apparatus for decoding of claim 1, wherein the BWE module comprises a switch which is configured to switch between the first and second time portion from the first decoder to the second decoder so that the bandwidth extension algorithm is either applied to the first decoded signal or to the second decoded signal.

4. The apparatus for decoding of claim 3, wherein the controller is configured to control the switch dependent on the indicated decoding algorithm within the coding mode information.

5. The apparatus for decoding of claim 1, wherein the controller is configured to increase the crossover frequency within the first time portion or to decrease the crossover frequency within the second time portion.

6. 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.

7. The apparatus for encoding of claim 6, further comprising an output interface for outputting the 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 coding mode information indicating the first decoding algorithm or the second decoding algorithm.

8. The apparatus for encoding of claim 6, 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.

9. The apparatus for encoding of claim 6, wherein the BWE module comprises a switch controlled by the decision stage, wherein the switch is configured to switch between the first and second time encoder so that the audio signal is for different time portions either encoded by the first or by the second encoder.

10. The apparatus for encoding of claim 6, wherein the decision stage is operative to analyze the audio signal or a first output of the first encoder or a second output of the second encoder or a signal acquired by decoding an output signal of the first encoder or the second encoder with respect to a target function.

11. 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.

12. 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.

13. An encoded audio signal comprising:

a first portion encoded in accordance with a first encoding algorithm, the first encoding algorithm comprising an LPC-based coder;

a second portion encoded in accordance with a second different encoding algorithm, the second encoding algorithm comprising a transform-based coder;

bandwidth extension parameters for the first portion and the second portion; and

a coding mode information indicating a first crossover frequency used for the first portion or a second crossover frequency used for the second portion, wherein the first crossover frequency is higher than the second crossover frequency.

14. 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.