Multi-mode audio codec and CELP coding adapted therefore

• US 9,495,972 B2
• Filed: 05/27/2014
• Issued: 11/15/2016
• 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 Foerderung Der Angewandten Forsching E.V.
• Inventors: Geiger, Ralf, Fuchs, Guillaume, Multrus, Markus, Grill, Bernhard
• Primary Examiner(s): PULLIAS, JESSE SCOTT
• Application Number:
  US14/288,091
• Publication Number:
  US 20140343953A1
• Time in Patent Office: 903 Days
• Field of Search: 704200-230
• US Class Current: 1/1
• 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 decoder for decoding an audio signal from a bitstream, comprising:

an excitation generator configured to generate a current excitation for a current frame of the bitstream having the audio signal encoded therein, by

constructing an adaptive codebook excitation based on a past excitation and an adaptive codebook index for the current frame within the bitstream;

constructing an innovation codebook excitation based on an innovation codebook index for the current frame within the bitstream;

computing an estimate of an energy of the innovation codebook excitation spectrally weighted by a weighted linear prediction synthesis filter constructed from linear prediction filter coefficients within the bitstream;

setting a gain of the innovation codebook excitation based on a ratio between a global gain value within the bitstream and the estimated energy; and

combining the adaptive codebook excitation and the innovation codebook excitation to achieve the current excitation; and

a linear prediction synthesis filter configured to filter the current excitation based on the linear prediction filter coefficients.

2. The CELP decoder according to claim 1, wherein the excitation generator is configured to, in constructing the adaptive codebook excitation, filter the past excitation with a filter depending on the adaptive codebook index.

3. The CELP decoder according to claim 1, wherein the excitation generator is configured to construct the innovation codebook excitation such that the latter comprises a zero vector with a number of non-zero pulses, the number and positions of the non-zero pulses being indicated by the innovation codebook index.

4. The CELP decoder according to according to claim 1, wherein the excitation generator is configured to, in computing the estimate of the energy of the innovation codebook excitation, filter the innovation codebook excitation with

5. The CELP decoder according to claim 1, wherein the excitation generator is configured to, in combining the adaptive codebook excitation and the innovation codebook excitation, form a weighted sum of the adaptive codebook excitation weighted with a weighting factor depending on the adaptive codebook index, and the innovation codebook excitation weighted with the gain.

6. A CELP decoding method for decoding an audio signal from a bitstream, comprising:

generating a current excitation for a current frame of the bitstream having the audio signal encoded therein, by

constructing an adaptive codebook excitation based on a past excitation and an adaptive codebook index for the current frame within the bitstream;

constructing an innovation codebook excitation based on an innovation codebook index for the current frame within the bitstream;

computing an estimate of an energy of the innovation codebook excitation spectrally weighted by a weighted linear prediction synthesis filter constructed from linear prediction filter coefficients within the bitstream;

setting a gain of the innovation codebook excitation based on a ratio between a global gain value within the bitstream and the estimated energy; and

combining the adaptive codebook excitation and the innovation codebook excitation to achieve the current excitation; and

filtering the current excitation based on the linear prediction filter coefficients by a linear prediction synthesis filter.

7. 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 6.