Audio codec supporting time-domain and frequency-domain coding modes

• US 9,037,457 B2
• Filed: 08/13/2013
• Issued: 05/19/2015
• 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: Geiger, Ralf, Schmidt, Konstantin, Grill, Bernhard, Lutzky, Manfred, Werner, Michael, Gayer, Marc, Hilpert, Johannes, Jaegers, Wolfgang, Valero, Maria L.
• Primary Examiner(s): PULLIAS, JESSE SCOTT
• Application Number:
  US13/966,048
• Publication Number:
  US 20130332174A1
• Time in Patent Office: 644 Days
• Field of Search: 704200-230, 704500-504
• US Class Current: 704/219
• 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 19/167 Audio streaming, i.e. formatting and decoding of an encoded audio signal representation into a data stream for transmission or storage purposes
• 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 25/78 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 audio codec supporting both, time-domain and frequency-domain coding modes, having low-delay and an increased coding efficiency in terms of iterate/distortion ratio, is obtained by configuring the audio encoder such that same operates in different operating modes such that if the active operative mode is a first operating mode, a mode dependent set of available frame coding modes is disjoined to a first subset of time-domain coding modes, and overlaps with a second subset of frequency-domain coding modes, whereas if the active operating mode is a second operating mode, the mode dependent set of available frame coding modes overlaps with both subsets, i.e. the subset of time-domain coding modes as well as the subset of frequency-domain coding modes.

Claims

1. An audio decoder comprising:

a time-domain decoder;

a frequency-domain decoder; and

an associator configured to associate each of consecutive frames of a data stream, each of which represents a corresponding one of consecutive portions of an audio signal, with one out of a mode dependent set of a plurality of frame coding modes,

wherein the time-domain decoder is configured to decode frames comprising one of a first subset of one or more of the plurality of frame coding modes associated therewith, and the frequency-domain decoder is configured to decode frames comprising one of a second subset of one or more of the plurality of frame coding modes associated therewith, the first and second subsets being disjoint to each other,

wherein the associator is configured to perform the association dependent on a frame mode syntax element associated with the frames in the data stream, and operate in an active one of a plurality of operating modes with selecting the active operating mode out of the plurality of operating modes depending on the data stream and/or an external control signal, and changing the dependency of the performance of the association depending on the active operating mode, and

where the time-domain decoder is a code-excited linear-prediction decoder.

2. The audio decoder according to claim 1, wherein the associator is configured such that if the active operating mode is a first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset, and

if the active operating mode is a second operating mode, the mode dependent set of the plurality of frame coding modes overlaps with the first and second subsets.

3. The audio decoder according to claim 1, wherein the frequency-domain decoder is a transform decoder configured to decode the frames comprising one of the second subset of one or more of the frame coding modes associated therewith, based on transform coefficient levels encoded therein.

4. An audio decoder comprising:

a time-domain decoder;

a frequency-domain decoder; and

an associator configured to associate each of consecutive frames of a data stream, each of which represents a corresponding one of consecutive portions of an audio signal, with one out of a mode dependent set of a plurality of frame coding modes,

wherein the time-domain decoder is configured to decode frames comprising one of a first subset of one or more of the plurality of frame coding modes associated therewith, and the frequency-domain decoder is configured to decode frames comprising one of a second subset of one or more of the plurality of frame coding modes associated therewith, the first and second subsets being disjoint to each other,

wherein the associator is configured to perform the association dependent on a frame mode syntax element associated with the frames in the data stream, and operate in an active one of a plurality of operating modes with selecting the active operating mode out of the plurality of operating modes depending on the data stream and/or an external control signal, and changing the dependency of the performance of the association depending on the active operating mode, and

wherein the frame mode syntax element is coded into the data stream so that a number of differentiable possible values for the frame mode syntax element relating to each frame is independent from the active operating mode being the first or second operating mode.

5. The audio decoder according to claim 4, wherein the number of differentiable possible values is two and the associator is configured such that, if the active operating mode is the first operating mode, the mode dependent set comprises a first and a second frame coding mode of the second subset of one or more frame coding modes, and the frequency-domain decoder is configured to use different time-frequency resolutions in decoding frames comprising the first and second frame coding mode associated therewith.

6. An audio decoder comprising:

a time-domain decoder;

a frequency-domain decoder; and

an associator configured to associate each of consecutive frames of a data stream, each of which represents a corresponding one of consecutive portions of an audio signal, with one out of a mode dependent set of a plurality of frame coding modes,

wherein the time-domain decoder is configured to decode frames comprising one of a first subset of one or more of the plurality of frame coding modes associated therewith, and the frequency-domain decoder is configured to decode frames comprising one of a second subset of one or more of the plurality of frame coding modes associated therewith, the first and second subsets being disjoint to each other,

wherein the associator is configured to perform the association dependent on a frame mode syntax element associated with the frames in the data stream, and operate in an active one of a plurality of operating modes with selecting the active operating mode out of the plurality of operating modes depending on the data stream and/or an external control signal, and changing the dependency of the performance of the association depending on the active operating mode, and

wherein the time-domain decoder and the frequency-domain decoder are LP based decoders configured to acquire linear prediction filter coefficients for each frame from the data stream, wherein the time-domain decoder is configured to reconstruct the portions of the audio signal corresponding to the frames comprising one of the first subset of one or more of the frame coding modes associated therewith by applying an LP synthesis filter depending on the LPC filter coefficients for the frames comprising one of the first subset of one or more of the plurality of frame coding modes associated therewith, onto an excitation signal constructed using codebook indices in the frames comprising one of the first subset of one or more of the plurality of frame coding modes associated therewith, and the frequency-domain decoder is configured to reconstruct the portions of the audio signal corresponding to the frames comprising one of the second subset of one or more of the frame coding modes associated therewith by shaping an excitation spectrum defined by transform coefficient levels in the frames comprising one of the second subset associated therewith, in accordance with the LPC filter coefficients for the frames comprising one of the second subset associated therewith, and retransforming the shaped excitation spectrum.

7. An audio encoder comprising:

a time-domain encoder;

a frequency-domain encoder; and

an associator configured to associate each of consecutive portions of an audio signal with one out of a mode dependent set of a plurality of frame coding modes,

wherein the time-domain encoder is configured to encode portions comprising one of a first subset of one or more of the plurality of frame coding modes associated wherewith, into a corresponding frame of a data stream, and wherein the frequency-domain encoder is configured to encode portions comprising one of a second subset of one or more of the plurality of encoding modes associated therewith, into a corresponding frame of the data stream,

wherein the associator is configured to operate in an active one of a plurality of operating modes such that, if the active operating mode is a first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset and if the active operating mode is a second operating mode, the mode dependent set of the plurality of encoding modes overlaps with the first and second subset, and

wherein the time-domain encoder is a code-excited linear-prediction encoder.

8. The audio encoder according to claim 7, wherein the associator is configured to encode a frame mode syntax element into the data stream so as to indicate, for each portion, as to which frame coding mode of the plurality of frame coding modes the respective portion is associated with.

9. The audio encoder according to claim 8, wherein the associator is configured such that if the active operating mode is the first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset, and

if the active operating mode is a second operating mode, the mode dependent set of the plurality of frame coding modes overlaps with the first and second subsets.

10. The audio encoder according to claim 7, wherein the frequency-domain encoder is a transform encoder configured to encode the portions comprising one of the second subset of one or more of the frame coding modes associated therewith, using transform coefficient levels and encode same into the corresponding frames of the data stream.

11. An audio encoder comprising:

a time-domain encoder;

a frequency-domain encoder; and

an associator configured to associate each of consecutive portions of an audio signal with one out of a mode dependent set of a plurality of frame coding modes,

wherein the time-domain encoder is configured to encode portions comprising one of a first subset of one or more of the plurality of frame coding modes associated wherewith, into a corresponding frame of a data stream, and wherein the frequency-domain encoder is configured to encode portions comprising one of a second subset of one or more of the plurality of encoding modes associated therewith, into a corresponding frame of the data stream,

wherein the associator is configured to operate in an active one of a plurality of operating modes such that, if the active operating mode is a first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset and if the active operating mode is a second operating mode, the mode dependent set of the plurality of encoding modes overlaps with the first and second subset,

wherein the associator is configured to encode a frame mode syntax element into the data stream so as to indicate, for each portion, as to which frame coding mode of the plurality of frame coding modes the respective portion is associated with, and

wherein the associator is configured to encode the frame mode syntax element into the data stream using a bijective mapping between a set of possible values of the frame mode syntax element associated with a respective portion on the one hand, and the mode dependent set of the frame coding modes on the other hand, which bijective mapping changes depending on the active operating mode.

12. An audio encoder comprising:

a time-domain encoder;

a frequency-domain encoder; and

an associator configured to associate each of consecutive portions of an audio signal with one out of a mode dependent set of a plurality of frame coding modes,

wherein the time-domain encoder is configured to encode portions comprising one of a first subset of one or more of the plurality of frame coding modes associated wherewith, into a corresponding frame of a data stream, and wherein the frequency-domain encoder is configured to encode portions comprising one of a second subset of one or more of the plurality of encoding modes associated therewith, into a corresponding frame of the data stream,

wherein the associator is configured to operate in an active one of a plurality of operating modes such that, if the active operating mode is a first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset and if the active operating mode is a second operating mode, the mode dependent set of the plurality of encoding modes overlaps with the first and second subset,

wherein the associator is configured to encode a frame mode syntax element into the data stream so as to indicate, for each portion, as to which frame coding mode of the plurality of frame coding modes the respective portion is associated with,

wherein the associator is configured such that if the active operating mode is the first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset, and

if the active operating mode is a second operating mode, the mode dependent set of the plurality of frame coding modes overlaps with the first and second subsets, and

wherein a number of possible values in the set of possible values is two and the associator is configured such that, if the active operating mode is the first operating mode, the mode dependent set comprises a first and a second frame coding mode of the second set of one or more frame coding modes, and the frequency-domain encoder is configured to use different time-frequency resolutions in encoding portions comprising the first and second frame coding mode associated therewith.

13. An audio encoder comprising:

a time-domain encoder;

a frequency-domain encoder; and

an associator configured to associate each of consecutive portions of an audio signal with one out of a mode dependent set of a plurality of frame coding modes,

wherein the time-domain encoder is configured to encode portions comprising one of a first subset of one or more of the plurality of frame coding modes associated wherewith, into a corresponding frame of a data stream, and wherein the frequency-domain encoder is configured to encode portions comprising one of a second subset of one or more of the plurality of encoding modes associated therewith, into a corresponding frame of the data stream,

wherein the associator is configured to operate in an active one of a plurality of operating modes such that, if the active operating mode is a first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset and if the active operating mode is a second operating mode, the mode dependent set of the plurality of encoding modes overlaps with the first and second subset, and

wherein the time-domain decoder and the frequency-domain decoder are LP based encoders configured to signal LPC-filter coefficients for each portion of the audio signal, wherein the time-domain encoder is configured to apply an LP analysis filter depending on the LPC filter coefficients onto the portions of the audio signal comprising one of the first subset of one or more of the frame coding modes associated therewith so as to acquire an excitation signal, and to approximate the excitation signal by use of codebook indices and insert same into the corresponding frames, wherein the frequency-domain encoder is configured to transform the portions of the audio signal comprising one of the second subset of one or more of the frame coding modes associated therewith, so as to acquire a spectrum, and shaping the spectrum in accordance with the LPC filter coefficients for the portions comprising one of the second subset associated therewith, so as to acquire an excitation spectrum, quantize the excitation spectrum into transform coefficient levels in the frames comprising one of the second subset associated therewith, and insert the quantized excitation spectrum into the corresponding frames.

14. An audio decoding method using a time-domain decoder, and a frequency-domain decoder, the method comprising:

associating each of consecutive frames of a data stream, each of which represents a corresponding one of consecutive portions of an audio signal, with one out of a mode dependent set of a plurality of frame coding modes;

decoding frames comprising one of a first subset of one or more of the plurality of frame coding modes associated therewith, by the time-domain decoder; and

decoding frames comprising one of a second subset of one or more of the plurality of frame coding modes associated therewith, by the frequency-domain decoder, the first and second subsets being disjoint to each other,

wherein the association is dependent on a frame mode syntax element associated with the frames in the data stream,

wherein the association is performed in an active one of a plurality of operating modes with selecting the active operating mode out of the plurality of operating modes depending on the data stream and/or an external control signal, such that the dependency of the performance of the association changes depending on the active operating mode, and

wherein the time-domain decoder is a code-excited linear-production decoder.

16. A non-transitory computer -readable medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method according to claim 14.

15. An audio encoding method using a time-domain encoder and a frequency-domain encoder, the method comprising:

associating each of consecutive portions of an audio signal with one out of a mode dependent set of a plurality of frame coding modes;

encoding portions comprising one of a first subset of one or more of the plurality of frame coding modes associated wherewith, into a corresponding frame of a data stream by the time-domain encoder; and

encoding portions comprising one of a second subset of one or more of the plurality of encoding modes associated therewith, into a corresponding frame of the data stream by the frequency-domain encoder,

wherein the association is performed in an active one of a plurality of operating modes such that, if the active operating mode is a first operating mode, the mode dependent set of the plurality of frame coding modes is disjoint to the first subset and overlaps with the second subset and if the active operating mode is a second operating mode, the mode dependent set of the plurality of encoding modes overlaps with the first and second subset, and

wherein the time-domain encoder is a code-excited linear-prediction encoder.

17. A non-transitory computer-readable medium having store thereon a computer program comprising a program code for performing, when running on a computer, a method according to claim 15.