Apparatus and method for coding a portion of an audio signal using a transient detection and a quality result

• US 9,620,129 B2
• Filed: 08/14/2013
• Issued: 04/11/2017
• Est. Priority Date: 02/14/2011
• 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: Helmrich, Christian, Fuchs, Guillaume, Markovic, Goran
• Primary Examiner(s): COLUCCI, MICHAEL C
• Application Number:
  US13/966,688
• Publication Number:
  US 20130332177A1
• Time in Patent Office: 1,336 Days
• Field of Search: 704223, 704203, 704219, 704205, 704500, 375243, 381 98
• CPC Class Codes: G10K 11/16 Methods or devices for protecting against, or for damping, noise or other acoustic waves in general G10K11/36 takes precedence
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• 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 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 19/03 Spectral prediction for preventing pre-echo; Temporary noise shaping [TNS], e.g. in MPEG2 or MPEG4
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 19/107 Sparse pulse excitation, e.g. by using algebraic codebook
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 19/22 Mode decision, i.e. based on audio signal content versus external parameters
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 21/0216 characterised by the method used for estimating noise
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients
• CPC Class Codes: G10L 25/51 for comparison or discrimination
• CPC Class Codes: G10L 25/69 for evaluating synthetic or decoded voice signals
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10

Abstract

An apparatus for coding a portion of an audio signal to obtain an encoded audio signal for the portion of the audio signal includes a transient detector for detecting whether a transient signal is located in the portion of the audio signal to obtain a transient detection result, an encoder stage for performing first and second encoding algorithms on the audio signal, the first and second encoding algorithms having differing first and second characteristics, respectively, a processor for determining which encoding algorithm results in an encoded audio signal being a better approximation to the portion of the audio signal with respect to the other encoding algorithm to obtain a quality result, and a controller for determining whether the encoded audio signal for the portion of the audio signal is to be generated by either the first or the second encoding algorithm based on the transient-detection and quality results.

Claims

1. An apparatus for coding a portion of an audio signal to acquire an encoded audio signal for the portion of the audio signal, comprising:

a transient detector configured for detecting whether a transient signal is located in the portion of the audio signal to achieve a transient detection result for the portion of the audio signal;

an encoder stage configured for performing a first encoding algorithm on the portion of the audio signal to obtain a first quality result value for the portion of the audio signal, the first encoding algorithm comprising a first characteristic, and for performing a second encoding algorithm on the same portion of the audio signal from which the first quality result value was derived, to obtain a second quality result value for the portion of the audio signal, the second encoding algorithm comprising a second characteristic being different from the first characteristic;

a processor configured for determining which encoding algorithm of the first and second encoding algorithms results in the encoded audio signal for the portion of the audio signal being a better approximation to the portion of the audio signal with respect to the other encoding algorithm of the first and second encoding algorithms to achieve a quality result for the portion of the audio signal, wherein the processor is configured to determine the quality result as a distance between the first quality result value and the second quality result value;

a controller configured for determining whether the encoded audio signal for the portion of the audio signal is to be generated using either the first encoding algorithm or the second encoding algorithm based on the transient detection result for the portion of the audio signal and the quality result for the same portion of the audio signal; and

an output interface for outputting, for the portion of the audio signal, the encoded signal being either generated using the first encoding algorithm or generated using the second encoding algorithm,

wherein the encoder stage is configured for using the first encoding algorithm which is better suited for transient signals than the second encoding algorithm,

wherein the controller is configured for determining the second encoding algorithm, although the quality result indicates a better quality for the first encoding algorithm, when the transient detection result indicates a non-transient signal and when the quality result indicates a distance between the encoding algorithms, which is smaller than a threshold distance value, or

wherein the controller is configured for determining the first encoding algorithm, although the quality result indicates a better quality for the second encoding algorithm, when the transient detection result indicates a transient signal and when the quality result indicates the distance between the encoding algorithms, which is smaller than the threshold distance value, and

wherein at least one of the transient detector, the encoder stage, the processor, the controller, or the output interface comprises a hardware implementation.

2. The apparatus of claim 1, wherein the first encoding algorithm is an ACELP coding algorithm, and wherein the second encoding algorithm is a transform coding algorithm.

3. The apparatus in accordance with claim 1, wherein the threshold distance value is equal to or lower than 3 dB, and wherein the quality result values for both encoding algorithms are calculated using an SNR calculation between the audio signal and an encoded and again decoded version of the audio signal.

4. The apparatus in accordance with claim 1, wherein the controller is configured to only determine the second encoding algorithm or the first encoding algorithm, when a number of earlier signal portions for which the first or second encoding algorithm has been determined is smaller than a predetermined number.

5. The apparatus in accordance with claim 4, wherein the controller is configured to use a predetermined value being smaller than 10.

6. The apparatus in accordance with claim 1,

wherein the controller is configured for applying a hysteresis processing so that the second encoding algorithm or the first encoding algorithm is only determined when the lower quality result value among the first and the second quality result values indicates a lower quality for the second encoding algorithm or the first encoding algorithm, when a number of earlier signal portions comprising the first encoding algorithm or the second encoding algorithm, respectively, is equal or lower than a predetermined number, and when the transient detection result indicates a predefined state of the two possible states comprising non-transients and transients.

7. The apparatus in accordance with claim 1, wherein the transient detector is configured to perform the following:

high-pass filtering of the audio signal to acquire a high-pass filtered signal block;

subdividing of the high-pass filtered signal block into a plurality of sub-blocks;

calculating an energy for each sub-block;

combining of the energy values for each pair of adjacent sub-blocks to achieve a result for each pair; and

combining of the results for the pairs to achieve the transient detection result.

8. The apparatus in accordance with claim 1, wherein the encoder stage further comprises an LPC filtering stage for determining LPC coefficients from the audio signal for filtering the audio signal using an LPC analysis filter determined by the LPC coefficients to determine a residual signal, wherein the first encoding algorithm or the second encoding algorithm is applied to the residual signal, and

wherein the encoded audio signal further comprises information on the LPC coefficients.

9. The apparatus in accordance with claim 1,

wherein the encoding stage either comprises a switch connected to the first encoding algorithm and the second encoding algorithm or a switch connected subsequently to the first encoding algorithm and the second encoding algorithm, wherein the switch is controlled by the controller.

10. A method of coding a portion of an audio signal to acquire an encoded audio signal for the portion of the audio signal, comprising:

detecting, by a transient detector, whether a transient signal is located in the portion of the audio signal to achieve a transient detection result for the portion of the audio signal;

performing, by an encoder stage, a first encoding algorithm on the portion of the audio signal to obtain a first quality result value for the portion of the audio signal, the first encoding algorithm comprising a first characteristic, and performing a second encoding algorithm on the same portion of the audio signal from which the first quality result value was derived, to obtain a second quality result value for the portion of the audio signal, the second encoding algorithm comprising a second characteristic being different from the first characteristic;

determining, by a processor, which encoding algorithm of the first and second encoding algorithms results in the encoded audio signal being a better approximation to the portion of the audio signal with respect to the other encoding algorithm of the first and second encoding algorithms to achieve a quality result for the portion of the audio signal, wherein the determining comprises determining the quality result as a distance between the first quality result value and the second quality result value; and

determining, by a controller, whether the encoded audio signal for the portion of the audio signal is to be generated using either the first encoding algorithm or the second encoding algorithm based on the transient detection result for the same portion of the audio signal and the quality result for the portion of the audio signal; and

outputting, by an output interface, for the portion of the audio signal, the encoded signal being either generated using the first encoding algorithm or generated using the second encoding algorithm,

wherein the first encoding algorithm is better suited for transient signals than the second encoding algorithm,

wherein the determining whether the encoded audio signal for the portion of the audio signal is to be generated using either the first encoding algorithm or the second encoding algorithm comprises determining the second encoding algorithm, although the quality result indicates a better quality for the first encoding algorithm, when the transient detection result indicates a non-transient signal and when the quality result indicates a distance between the encoding algorithms, which is smaller than a threshold distance value, or

wherein the determining whether the encoded audio signal for the portion of the audio signal is to be generated using either the first encoding algorithm or the second encoding algorithm comprises determining the first encoding algorithm, although the quality result indicates a better quality for the second encoding algorithm, when the transient detection result indicates a transient signal and when the quality result indicates the distance between the encoding algorithms, which is smaller than the threshold distance value,

wherein at least one of the transient detector, the encoder stage, the processor, the controller, or the output interface comprises a hardware implementation.

11. A non-transitory storage medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method of coding a portion of an audio signal to acquire an encoded audio signal for the portion of the audio signal, the method comprising:

detecting whether a transient signal is located in the portion of the audio signal to achieve a transient detection result for the portion of the audio signal;

performing a first encoding algorithm on the portion of the audio signal to obtain a first quality result value for the portion of the audio signal, the first encoding algorithm comprising a first characteristic, and performing a second encoding algorithm on the same portion of the audio signal from which the first quality result value was derived to obtain a second quality result value for the portion of the audio signal, the second encoding algorithm comprising a second characteristic being different from the first characteristic;

determining which encoding algorithm of the first and second encoding algorithms results in the encoded audio signal being a better approximation to the portion of the audio signal with respect to the other encoding algorithm of the first and second encoding algorithms to achieve a quality result for the portion of the audio signal, wherein the determining comprises determining the quality result as a distance between the first quality result value and the second quality result value;

determining whether the encoded audio signal for the portion of the audio signal is to be generated using either the first encoding algorithm or the second encoding algorithm based on the transient detection result for the same portion of the audio signal and the quality result for the portion of the audio signal; and

outputting, for the portion of the audio signal, the encoded signal being either generated using the first encoding algorithm or generated using the second encoding algorithm,

wherein the first encoding algorithm is better suited for transient signals than the second encoding algorithm,

wherein the determining whether the encoded audio signal for the portion of the audio signal is to be generated using either the first encoding algorithm or the second encoding algorithm comprises determining the second encoding algorithm, although the quality result indicates a better quality for the first encoding algorithm, when the transient detection result indicates a non-transient signal and when the quality result indicates a distance between the encoding algorithms, which is smaller than a threshold distance value, or

wherein the determining whether the encoded audio signal for the portion of the audio signal is to be generated using either the first encoding algorithm or the second encoding algorithm comprises determining the first encoding algorithm, although the quality result indicates a better quality for the second encoding algorithm, when the transient detection result indicates a transient signal and when the quality result indicates the distance between the encoding algorithms, which is smaller than the threshold distance value.