Audio encoder and decoder with pitch prediction

• US 9,558,754 B2
• Filed: 04/12/2016
• Issued: 01/31/2017
• Est. Priority Date: 07/02/2010
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Villemoes, Lars, Resch, Barbara, Kjrling, Kristofer
• Primary Examiner(s): COLUCCI, MICHAEL C
• Application Number:
  US15/097,201
• Publication Number:
  US 20160225381A1
• Time in Patent Office: 294 Days
• Field of Search: 704/207, 704/201, 704/203, 704/219, 704/222, 704/501, 375/243, 375/350, 725/62
• US Class Current: 1/1
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor
• 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 19/125 Pitch excitation, e.g. pitch synchronous innovation CELP [PSI-CELP]
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding
• 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 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: G10L 21/003 Changing voice quality, e.g. pitch or formants
• CPC Class Codes: G10L 21/007 characterised by the process used
• CPC Class Codes: G10L 21/013 Adapting to target pitch

Abstract

In one embodiment, an audio decoder for decoding an encoded audio bitstream is disclosed. The audio decoder is capable of being operated in at least three different decoding modes. The audio decoder includes a demultiplexer for obtaining audio data and control information from the encoded audio bitstream. The audio decoder also includes a first audio decoder configured to operate in a first decoding mode using a first decoding technique and a second audio decoder configured to operate in a second decoding mode using a second decoding technique. The audio decoder also includes a pitch predictor integrated into the second audio decoder. The pitch predictor includes a long-term prediction filter and a short-term prediction filter. The audio decoder further includes a selector for selecting one of the at least three different decoding modes based on at least some of the control information.

Claims

1. An audio decoding processor for decoding an encoded audio bitstream, the audio decoding processor capable of being operated in one of at least two different decoding modes and comprising:

a demultiplexer for obtaining audio data and control information from the encoded audio bitstream;

a first audio decoder configured to operate in a first decoding mode using a first decoding technique;

a second audio decoder configured operate in a second decoding mode using a second decoding technique, the second decoding technique being different from the first decoding technique;

a pitch predictor integrated into the second audio decoder, the pitch predictor including a long-term prediction filter and a short-term prediction filter;

a selector for selecting one of the at least two different decoding modes based on first control information obtained from the encoded audio bitstream;

a pitch enhancement filter that is selectively operated in either an active mode or an inactive mode based on second control information obtained from the encoded audio bitstream that is independent of the first control information for selecting the decoding mode, wherein the active mode causes the pitch enhancement filter to filter a preliminary audio signal generated by the first audio decoder or the second audio decoder and the inactive mode causes the pitch enhancement filter to not filter the preliminary audio signal; and

an output interface for outputting a decoded audio signal, the decoded audio signal being processed at least in part by the first audio decoder or the second audio decoder.

2. The audio decoding processor of claim 1 wherein the first decoding mode includes frequency domain coding and the second decoding mode includes linear prediction coding.

3. The audio decoding processor of claim 1 wherein short-term prediction filter is arranged in series with the long-term prediction filter so that the short-term prediction filter directly follows the long-term prediction filter.

4. The audio decoding processor of claim 1 wherein the long-term prediction filter is configured to restore a pitch of an audio signal represented by the audio data and the short-term prediction filter is configured to restore formants of the audio signal.

5. The audio decoder of claim 1 wherein the pitch enhancement filter is configured to attenuate noise in spectral valleys.

6. The audio decoding processor of claim 1 wherein the control information includes a pitch enhancement control parameter and the pitch enhancement filter is selectively operated in either the active mode or the inactive mode based on the value of the pitch enhancement control parameter.

7. The audio decoding processor of claim 1 wherein the pitch enhancement filter is capable of suppressing noise components located between harmonics of a detected pitch.

8. The audio decoding processor of claim 1 wherein the control information includes a coding mode parameter and the selector uses the coding mode parameter to select a current coding mode from one of the at least two different decoding modes.

9. The audio decoding processor of claim 8 wherein the audio decoding processor is capable of being dynamically switched between the at least two different decoding modes based on a value of the coding mode parameter.

10. The audio decoding processor of claim 1 wherein the control information includes a coding mode parameter and a pitch enhancement control parameter, wherein the coding mode parameter and the pitch enhancement control parameter are independent so that a value of the pitch enhancement control parameter may change when a value of the coding mode parameter does not change.

11. A method for decoding an encoded audio bitstream with an audio decoding processor having at least two different decoding modes, the method comprising:

extracting audio data and control information from the encoded audio bitstream;

selecting one of the at least two different decoding modes based on first control information;

decoding the audio data in either a first audio decoder or a second audio decoder to obtain a preliminary audio signal, the first audio decoder configured to operate in a first decoding mode using a first decoding technique and the second audio decoder configured to operate in a second decoding mode using a second decoding technique, the second decoding technique being different from the first decoding technique;

determining that the audio decoding processor is operating in the second decoding mode based on at least some of the control information;

filtering the preliminary audio signal with a pitch predictor, the pitch predictor including a long-term prediction filter and a short-term prediction filter;

determining whether a pitch enhancement filter is operating in an active mode or an inactive mode based on second control information that is independent of the first control information for selecting the decoding mode, wherein the active mode causes the pitch enhancement filter to filter the preliminary audio signal generated by the second audio decoder and the inactive mode causes the pitch enhancement filter to not filter the preliminary audio signal; and

outputting a decoded audio signal, the decoded audio signal being processed at least in part by the first audio decoder or the second audio decoder.

12. An audio encoding processor for encoding an input audio signal, the audio encoding processor capable of being operated in one of at least two different encoding modes and comprising:

a first audio encoder configured to operate in a first encoding mode using a first encoding technique;

a second audio encoder configured to operate in a second encoding mode using a second encoding technique, the second encoding technique being different from the first encoding technique;

a pitch predictor integrated into the second audio encoder, the pitch predictor including a long-term prediction filter and a short-term prediction filter;

a selector for selecting one of the at least two different encoding modes based on control information;

a multiplexer for combining audio data and the control information into an encoded audio bitstream, where the control information includes first control information for selecting a decoding mode in an audio decoding processor and second control information, independent of the first control information, the second control information for specifying an active or inactive mode for a pitch enhancement filter in the audio decoding processor configured to receive the encoded audio signal bitstream, the active mode causing the pitch enhancement filter to filter a preliminary audio signal generated by a first audio decoder or a second audio decoder in the audio decoding processor and the inactive mode causing the pitch enhancement filter to not filter the preliminary audio signal; and

an output interface for outputting the encoded audio bitstream.