Abstract: A method is provided for attenuating pre-echoes in a digital audio signal generated from a transform encoding, comprising, upon decoding and for a current frame of said digital audio signal: defining a concatenated signal from at least the reconstructed signal of the current frame, dividing said concatenated signal into subunits of samples having a predetermined length, calculating the time envelope of the concatenated signal, detecting the transition of the time envelope towards a high-energy area, determining the low-energy sub-units preceding a subunit in which a transition has been detected, and an attenuation step in said determined subunits. The attenuation is carried out according to an attenuation factor calculated for each of the determined subunits, based on the time envelope of the concatenated signal. The invention also relates to a device for implementing said method, and to a decoder including such a device.

Abstract: A method of bitrate switching on decoding an audio signal coded by a audio coding system, said decoding comprising a post-processing step depending on the bitrate. On switching from an initial bitrate to a final bitrate, said method includes a transition step of continuous change from a signal at the initial bitrate to a signal at the final bitrate, one or both of said signals being post-processed. Application to transmission of VoIP speech and/or audio signals in data packet networks.

Abstract: The present invention relates to a method of transmission error concealment in a digital signal split up into a plurality of successive frames associated with different time intervals in which, on reception, the signal might comprise erased frames and valid frames and in order to replace at least the first erased frame (N) after a valid frame, at least two steps are performed, a first step (E1) of preparation not producing any missing sample and comprising at least one analysis of a valid decoded signal and a second step (E2) of concealment producing the missing samples of the signal corresponding to said erased frame. The first step and the second step are executed in different time intervals. The invention relates also to a device of concealment implementing the method according to the invention as well as a decoder comprising such a device. The invention allows the distribution of the error concealment complexity on different time intervals.

Abstract: The invention relates to a method for scalar quantization-based coding of the samples of a digital audio signal (S), the samples being coded over a pre-determined number of bits in order to obtain a binary frame of quantization indices (IPCM), the coding being carried out according to an amplitude compression law, where a pre-determined number of least significant bits are not taken into account in the binary frame of quantization indices. The coding method comprises the steps for storing (27) at least a part of the least significant bits that are not taken into account in the quantization index binary frame and for determination (28) of an enhancement bit stream (IEXT) comprising at least one bit thus stored.

Abstract: An encoder and a method for encoding a digital signal are provided. The method includes encoding a preceding frame of samples of the digital signal according to a predictive encoding process, and encoding a current frame of samples of the digital signal according to a transform encoding process. The method is implemented such that a first portion of the current frame is also encoded by predictive encoding that is limited relative to the predictive encoding of the preceding frame by reusing at least one parameter of the predictive encoding of the preceding frame and only encoding the parameters of said first portion of the current frame that are not reused. A decoder and a decoding method are also provided, which correspond to the described encoding method.

Abstract: The invention relates to the processing of a digital signal originating from a decoder and a noise reduction post-processing step, including, in particular, limitation of distortion introduced by the post-processing step in order to deliver a corrected output signal (SOUT), assigning said corrected output signal (SOUT) with: a current amplitude having an intermediary value between a current amplitude value of the post-processed signal (SPOST) and a corresponding current amplitude value of the decoded signal (S?MIC), or the current amplitude of the post-processed signal (SPOST), according to the respective values of the current amplitude of the post-processed signal (SPOST) and by the corresponding current amplitude of the decoded signal (S?MIC).

Abstract: A method and coding device are provided for coding a digital audio input signal in a hierarchical coder, which includes a core coding stage with B bits and at least one current improvement coding stage k, delivering quantization indices which are concatenated to form the indices of a preceding embedded coder. The method includes: obtaining possible quantization values for the current improvement stage k by determining absolute reconstruction levels of just the current stage k on the basis of the indices of the preceding embedded coder; and quantizing the input signal of the hierarchical coder having undergone or not a perceptual weighting processing, on the basis of the possible quantization values so as to form a scalar quantization index for the stage k and a quantized signal corresponding to one of the possible quantization values.

Abstract: A method and apparatus for the parametric encoding of a stereo digital-audio signal. The method includes encoding a mono signal produced by downmixing applied to the stereo signal and encoding spatialisation information of the stereo signal. Downmixing includes determining, for a predetermined set of frequency sub-bands, a phase difference between two stereo channels; obtaining an intermediate channel by rotating a first predetermined channel of the stereo signal through an angle obtained by reducing the phase difference; determining the phase of the mono signal from the phase of the signal that is the sum of the intermediate channel and the second stereo signal, and from a phase difference between, on the one hand, the signal that is the sum of the intermediate channel and the second channel and, on the other hand, the second channel of the stereo signal. Also provided are a decoding method, an encoder and a decoder.

Abstract: The invention relates to the coding/decoding of a signal into several sub-bands, in which at least a first and a second sub-bands which are adjacent are transform coded (601, 602). In particular, in order to apply a perceptual weighting, in the transformed domain, to at least the second sub-band, the method comprises:—determining at least one frequency masking threshold (606) to be applied on the second sub-band; and normalizing said masking threshold in order to provide a spectral continuity between the above-mentioned first and second sub-bands. An advantageous application of the invention involves a perceptual weighting of the high-frequency band in the TDAC transform coding of a hierarchical encoder according to standard G.729.1.

Abstract: A method and apparatus are provided for controlling the shaping of encoding noise during the ADPCM encoding of a digital audio input signal. The noise-shaping is carried out through the use of feedback that comprises filtering noise. The method includes the following steps: obtaining a parameter for indicating a high spectral dynamic range of the signal, the parameter indicating a risk of instability of the feedback; detecting a risk of instability by comparing the indication parameter to at least one predetermined threshold; limiting the feedback in the event that a risk of instability is detected; and gradually reactivating the feedback over a predetermined number of frames subsequent to the current frame for which the feedback is limited. Also provided is an encoder with feedback, including a control module implementing the control method as described.

Abstract: The present invention relates to signal modification before pitch period repetition for the synthesis of blocks lost on decoding digital audio signals. The effects of repetition of transitories, such as the plosives of a speech signal, are avoided by comparing the samples of a pitch period with those of the previous pitch period. The signal is modified preferentially by taking the minimum between a current sample (e(3)) of the last pitch period (Tj) and at least one sample (e(2?T0) of approximately the same position in the previous pitch period (Tj?1).

Abstract: The invention relates to a method of processing bit errors in a bit frame emanating from a digital audio coder, comprising a step of receiving a current bit frame liable to comprise bit errors. According to the invention, the bit frame comprises sensitive bits to be protected which are catalogued in at least one category according to the type of parameter that they code and the method furthermore comprises the steps of receiving protection bits, of reading the sensitive bits received in the current bit frame, the number of sensitive bits being lower than the number of bits of the bit frame, of detecting bit errors as a function of said protection bits received and of said sensitive bits received and in the event of detecting at least one erroneous bit in said bit frame, of modifying the current bit frame before decoding, as a function of the category in which the erroneous bit is catalogued.

Abstract: A system for coding a hierarchical audio signal, comprising, at least, a core layer using parametric coding by analysis by synthesis in a first frequency band, a band extension layer for widening said first frequency band into a second frequency band, or wideband. The system also comprises a wideband audio coding quality enhancement layer based on transform coding using a spectral parameter obtained from said band extension layer. Application to transmitting speech and/or audio signals over packet networks.

Abstract: A module (402) for binary coding of a signal envelope, comprising coding module (502) for coding a variable length first mode. The coding module for coding the first mode incorporates an envelope saturation detector and said coding module (402) further includes a second coding module (503) for coding a second mode in parallel with the coding module (502) for coding the first mode and a mode selector (504) adapted to select one of the two coding modes as a function of a code length criterion and of the result from the envelope saturation detector.

Abstract: A method and decoder are provided for parametrically decoding a stereo digital audio signal.

Abstract: The invention relates to a method for generating a vector quantization dictionary for a signal, of the type comprising a statistical analysis of driving vectors representing the signal determining a finite set of code vectors which are proxies for the said driving vectors, wherein the method also comprises modifying the said finite set of code vectors to impose a minimum distance between the modified code vectors two by two, these modified code vectors forming the said dictionary.

Abstract: A hierarchical audio coder for use in a frequency band divided into adjacent first and second sub-bands, the coder including: a core coder (305) for coding an original signal in the first sub-band of the frequency band; a stage (306) for calculating a residual signal (e) from the original signal and the signal from the core coder; a device (307) for perceptually weighting the residual signal (e). The perceptual weighting device includes a perceptually weighted filter (307) with gain compensation adapted to realize spectral continuity between the output signal of the perceptually weighted filter with gain compensation and the signal in the second sub-band. Application to transmitting and storing digital signals, such as audio-frequency speech, music, etc. signals.

Abstract: A parametric coding method and apparatus are provided for coding a multichannel digital audio signal. The method includes a coding step for coding a signal from a channel reduction matrixing of the multichannel signal. The coding method also includes: obtaining, for each frame of predetermined length, spatial information parameters of the multichannel signal; dividing the spatial information parameters into a plurality of blocks of parameters; selecting a block of parameters as a function of the index of the current frame; and coding the block of parameters selected for the current frame.

Abstract: A method of hierarchical coding of a digital audio frequency input signal into several frequency sub-bands, including a core coding of the input signal according to a first throughput and at least one enhancement coding of higher throughput, of a residual signal. The core coding uses a binary allocation according to an energy criterion. The method includes for the enhancement coding: calculating a frequency-based masking threshold for at least part of the frequency bands processed by the enhancement coding; determining a perceptual importance per frequency sub-band as a function of the masking threshold and as a function of the number of bits allocated for the core coding; binary allocation of bits in the frequency sub-bands processed by the enhancement coding, as a function of the perceptual importance determined; and coding the residual signal according to the bit allocation. Also provided are a decoding method, a coder and a decoder.

Abstract: A method is provided for hierarchical coding of a digital audio signal comprising, for a current frame of the input signal: a core coding, delivering a scalar quantization index for each sample of the current frame and at least one enhancement coding delivering indices of scalar quantization for each coded sample of an enhancement signal. The enhancement coding comprises a step of obtaining a filter for shaping the coding noise used to determine a target signal and in that the indices of scalar quantization of said enhancement signal are determined by minimizing the error between a set of possible values of scalar quantization and said target signal. The coding method can also comprise a shaping of the coding noise for the core bitrate coding. A coder implementing the coding method is also provided.