Multi-mode audio codec and CELP coding adapted therefore

• US 9,715,883 B2
• Filed: 05/12/2016
• Issued: 07/25/2017
• Est. Priority Date: 10/20/2009
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer-Gesellschaft ZUR Forderung Der Angewandten Forschung EV
• Inventors: Geiger, Ralf, Fuchs, Guillaume, Grill, Bernhard, Multrus, Markus
• Primary Examiner(s): PULLIAS, JESSE SCOTT
• Application Number:
  US15/153,501
• Publication Number:
  US 20160260438A1
• Time in Patent Office: 439 Days
• Field of Search: 704200-232, 704500-504
• 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 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• 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 19/20 using sound class specific coding, hybrid encoders or object based coding
• CPC Class Codes: G10L 2019/0002 Codebook adaptations

Abstract

In an embodiment, bitstream elements of sub-frames are encoded differentially to a global gain value so that a change of the global gain value results in an adjustment of an output level of the decoded representation of the audio content. Concurrently, the differential coding saves bits. Even further, the differential coding enables the lowering of the burden of globally adjusting the gain of an encoded bitstream. In another embodiment, a global gain control across CELP coded frames and transform coded frames is achieved by co-controlling the gain of the codebook excitation of the CELP codec, along with a level of the transform or inverse transform of the transform coded frames. In another embodiment, the gain value determination in CELP coding is performed in the weighted domain of the excitation signal.

Claims

1. A CELP encoder comprising

a linear prediction analyzer configured to generate linear prediction filter coefficients for a current frame of an audio content and encode the linear prediction filter coefficients into a bitstream;

an excitation generator configured to determine a current excitation of the current frame as a combination of an adaptive codebook excitation and an innovation codebook excitation, which, when filtered by a linear prediction synthesis filter based on the linear prediction filter coefficients, recovers the current frame, by

constructing the adaptive codebook excitation defined by a past excitation and an adaptive codebook index for the current frame and encoding the adaptive codebook index into the bitstream; and

constructing the innovation codebook excitation defined by an innovation codebook index for the current frame and encoding the innovation codebook index into the bitstream; and

an energy determiner configured to determine an energy of a version of the audio content of the current frame filtered a weighting filter, to acquire a global gain value and encoding the global gain value into the bitstream, the weighting filter construed from the linear prediction filter coefficients.

2. The CELP encoder according to claim 1, wherein the linear prediction analyzer is configured to determine the linear prediction filter coefficients by linear prediction analysis applied onto a windowed and, according to a predetermined pre-emphasis filter, pre-emphasized version of the audio content.

3. The CELP encoder according to claim 1, wherein the excitation generator is configured to, in constructing the adaptive codebook excitation and the innovation codebook excitation, minimize a perceptual weighted distortion measure relative to the audio content.

4. The CELP encoder according to claim 1, wherein the excitation generator is configured to, in constructing the adaptive codebook excitation and the innovation codebook excitation, minimize a perceptual weighted distortion measure relative to the audio content using a perceptual weighting filter

W(z)=A(z/γ

),

wherein γ

is a perceptual weighting factor and A(z) is 1/H(z), wherein H(z) is the linear prediction synthesis filter, and wherein the energy determiner is configured to use the perceptual weighting filter as a weighting filter.

5. The CELP encoder according to claim 1, wherein the excitation generator is configured to perform an excitation update to acquire a past excitation of a next frame, by

estimating an innovation codebook excitation energy estimate by filtering an innovation codebook vector defined by first information contained within the innovation codebook index with

6. A CELP encoding method comprising

performing linear prediction analysis to generate linear prediction filter coefficients for a current frame of an audio content and encode the linear prediction filter coefficients into a bitstream;

determining a current excitation of the current frame as a combination of an adaptive codebook excitation and an innovation codebook excitation, which, when filtered by a linear prediction synthesis filter based on the linear prediction filter coefficients , recovers the current frame, by

constructing the adaptive codebook excitation defined by a past excitation and an adaptive codebook index for the current frame and encoding the adaptive codebook index into the bitstream; and

constructing the innovation codebook excitation defined by an innovation codebook index for the current frame and encoding the innovation codebook index into the bitstream; and

determining an energy of a version of the audio content of the current frame filtered a weighting filter, to acquire a global gain value and encoding the global gain value into the bitstream, the weighting filter construed from the linear prediction filter coefficients.

7. A non-transitory computer readable storage medium storing a computer program comprising a program code for performing, when running on a computer, a method according to claim 6.