Pitch filter for audio signals

• US 10,236,010 B2
• Filed: 10/24/2017
• Issued: 03/19/2019
• 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: Resch, Barbara, Kjorling, Kristofer, Villemoes, Lars
• Primary Examiner(s): Abebe, Daniel
• Application Number:
  US15/792,589
• Publication Number:
  US 20180047405A1
• Time in Patent Office: 511 Days
• Field of Search: 704225
• 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 some embodiments, a pitch filter for filtering a preliminary audio signal generated from an audio bitstream is disclosed. The pitch filter has an operating mode selected from one of either: (i) an active mode where the preliminary audio signal is filtered using filtering information to obtain a filtered audio signal, and (ii) an inactive mode where the pitch filter is disabled. The preliminary audio signal is generated in an audio encoder or audio decoder having a coding mode selected from at least two distinct coding modes, and the pitch filter is capable of being selectively operated in either the active mode or the inactive mode while operating in the coding mode based on control information.

Claims

1. An audio decoder for decoding an encoded audio bitstream, the audio decoder comprising:

an input interface for receiving the encoded audio bitstream;

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

a first decoding module configured to operate in a first decoding mode;

a second decoding module configured to operate in a second decoding mode, the second decoding mode being different from the first decoding mode; and

a pitch filter having a transfer function, H_E(z), based at least in part on;

2. The audio decoder of claim 1 wherein the pitch filter is a bass post filter that provides low frequency pitch enhancement.

3. The audio decoder of claim 1 wherein the pitch filter is implemented using a long-term predictor having a transfer function, P_LT(z), based at least in part on:

4. The audio decoder of claim 1 wherein the control information includes information for controlling the operation of the pitch filter.

5. The audio decoder of claim 4 wherein the information is used by the audio decoder to enable or disable the pitch filter.

6. The audio decoder of claim 1 further comprising a third decoding module configured to operate in a third decoding mode, the third decoding mode being different from the first decoding mode and the second decoding mode.

7. The audio decoder of claim 6 wherein the first decoding mode includes frequency-domain coding, the second decoding mode includes algebraic code excited linear prediction (ACELP), and the third decoding mode includes transform coded excitation (TCX).

8. A method for decoding an encoded audio bitstream, the method comprising:

receiving the encoded audio bitstream;

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

decoding the audio data with a first decoding module configured to operate in a first decoding mode if the first decoding mode is indicated by a coding mode parameter included in the control information;

decoding the audio data with a second decoding module configured to operate in a second decoding mode if the second decoding mode is indicated by the coding mode parameter, the second decoding mode being different from the first decoding mode; and

a filtering an audio signal generated by the first decoding module or the second decoding module with a pitch filter having a transfer function, H_E(z), based at least in part on;