Selective bass post filter

• US 9,830,923 B2
• Filed: 11/20/2015
• Issued: 11/28/2017
• 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: Resch, Barbara, Kjrling, Kristofer, Villemoes, Lars
• Primary Examiner(s): ABEBE, DANIEL DEMELASH
• Application Number:
  US14/947,906
• Publication Number:
  US 20160118057A1
• Time in Patent Office: 739 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. A decoder system for decoding a bit stream signal as an audio time signal, the decoder system including:

a decoding section for decoding the bit stream signal as a preliminary audio time signal, wherein the decoding section comprises a code-excited linear prediction, CELP, decoding module and a transform-coded excitation, TCX, decoding module; and

an interharmonic noise attenuation post filter adapted to receive the preliminary audio time signal, and to supply the audio time signal, wherein the post filter comprises a control section for selectively operating the post filter in one of the following modes;

i) a filtering mode, wherein the post filter filters the preliminary audio time signal to obtain a filtered signal and supplies the filtered signal as the audio time signal; and

ii) a pass-through mode, wherein the post filter supplies the preliminary audio time signal as the audio time signal,

wherein the interharmonic noise attenuation depends on a value of a variable gain, and the control section is operable to enable the pass-through mode by setting the value of the variable gain to zero.

2. The decoder system of claim 1, wherein the decoding section selectively operates in one of the following modes:

a) the TCX module is enabled and the post filter is operated in the pass-through mode;

b) the CELP module is enabled and, in response to a post-filtering signal, the post filter is operated in the filtering mode; and

c) the CELP module is enabled and, in response to the post-filtering signal, the post filter is operated in the pass-through mode.

3. The decoder system of claim 2,

the decoding section further comprising an Advanced Audio Coding, AAC, decoding module for decoding a bit stream signal as an audio time signal,

the control section being adapted to operate the decoder also in the following mode:

d) the AAC module is enabled and the post filter is disabled.

4. The decoder system of claim 1,

wherein the post filter is adapted to attenuate only such spectral components which are located below a predetermined cut-off frequency.

5. The decoder system of claim 1,

wherein the bit stream signal is a Moving Pictures Experts Group, MPEG, bit stream and is segmented into time frames and the control section is adapted to disable an entire time frame or a sequence of entire time frames;

and

the control section is further adapted to receive, for each time frame, a data field associated with this time frame and is operable, responsive to the value of the data field, to disable the post filter, whereby the preliminary audio time signal is output as the audio time signal.

6. A method of decoding a bit stream signal as an audio time signal, comprising:

decoding the bit stream signal as a preliminary audio time signal in one of a plurality of decoding modes, the plurality of decoding modes comprising code-excited linear prediction, CELP, and transform-coded excitation, TCX, decoding modes; and

filtering the preliminary audio time signal with an interharmonic noise attenuation post-filter to obtain the audio time signal, wherein the post-filter comprises a control section for selectively operating the post-filter in one of the following modes;

i) a filtering mode, wherein the post filter filters the preliminary audio time signal to obtain a filtered signal and supplies the filtered signal as the audio time signal; and

ii) a pass-through mode, wherein the post-filter supplies the preliminary audio time signal as the audio time signal,

wherein the interharmonic noise attenuation depends on a value of a variable gain, and the control section is operable to enable the pass-through mode by setting the value of the variable gain to zero.

7. The method of claim 6, wherein decoding the bit stream signal as an audio time signal comprises selectively operating in one of the following modes:

a) enabling the TCX decoding mode and operating the post-filter in the pass-through mode;

b) enabling the CELP decoding mode and, in response to a post-filtering signal, operating the post-filter in the filtering mode; and

c) enabling the CELP decoding mode and, in response to the post-filtering signal, operating the post-filter in the pass-through mode.

8. The method of claim 7,

the decoding modes further comprising an Advanced Audio Coding, AAC, decoding mode for decoding a bit stream signal as an audio time signal,

the control section being adapted to operate the decoder also in the following mode:

d) the AAC decoding mode is enabled and the post filter is disabled.

9. The method of claim 6,

wherein the post filter is adapted to attenuate only such spectral components which are located below a predetermined cut-off frequency.

10. The method of claim 6,

wherein the bit stream signal is a Moving Pictures Experts Group, MPEG, bit stream and is segmented into time frames and the control section is adapted to disable an entire time frame or a sequence of entire time frames;

and

the control section is further adapted to receive, for each time frame, a data field associated with this time frame and is operable, responsive to the value of the data field, to disable the post filter, whereby the preliminary audio time signal is output as the audio time signal.

11. A non-transitory computer readable storage medium containing a program of instructions, which when executed by one or more processors, cause one or more devices to perform a method of decoding a bit stream signal as an audio time signal, the method comprising:

decoding the bit stream signal as a preliminary audio time signal in one of a plurality of decoding modes, the plurality of decoding modes comprising code-excited linear prediction, CELP, and transform-coded excitation, TCX, decoding modes; and

filtering the preliminary audio time signal with an interharmonic noise attenuation post-filter to obtain the audio time signal, wherein the post-filter comprises a control section for selectively operating the post-filter in one of the following modes;

i) a filtering mode, wherein the post filter filters the preliminary audio time signal to obtain a filtered signal and supplies the filtered signal as the audio time signal; and

ii) a pass-through mode, wherein the post-filter supplies the preliminary audio time signal as the audio time signal,

wherein the interharmonic noise attenuation depends on a value of a variable gain, and the control section is operable to enable the pass-through mode by setting the value of the variable gain to zero.

12. The medium of claim 11, wherein decoding the bit stream signal as an audio time signal comprises selectively operating in one of the following modes:

a) enabling the TCX decoding mode and operating the post-filter in the pass-through mode;

b) enabling the CELP decoding mode and, in response to a post-filtering signal, operating the post-filter in the filtering mode; and

c) enabling the CELP decoding mode and, in response to the post-filtering signal, operating the post-filter in the pass-through mode.

13. The medium of claim 12,

the decoding modes further comprising an Advanced Audio Coding, AAC, decoding mode for decoding a bit stream signal as an audio time signal,

the control section being adapted to operate the decoder also in the following mode:

d) the AAC decoding mode is enabled and the post filter is disabled.

14. The medium of any claim 11,

wherein the post filter is adapted to attenuate only such spectral components which are located below a predetermined cut-off frequency.

15. The medium of claim 11,

wherein the bit stream signal is a Moving Pictures Experts Group, MPEG, bit stream and is segmented into time frames and the control section is adapted to disable an entire time frame or a sequence of entire time frames;

and

the control section is further adapted to receive, for each time frame, a data field associated with this time frame and is operable, responsive to the value of the data field, to disable the post filter, whereby the preliminary audio time signal is output as the audio time signal.