France Telecom

Orange

Alain Le Guyader

Balazs Kovesi

Stéphane Ragot

Bruno Lozach

José Bollo

Catherine Quinquis

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.

Controlling a noise-shaping feedback loop in a digital audio signal encoder avoiding instability risk of the feedback

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.

Coding with noise shaping in a hierarchical coder

The invention concerns a method for trained discrimination and attenuation of echoes of a digital audio signal generated from a transform coding, which consists, for each current frame of the signal. In comparing (A) in real time, in at least one frequency band a variable derived from one characteristic of the echo generating signal with that of a non-echo generating signal at a threshold value, and deducing therefrom (B) the existence or non-existence (C) of an echo derived from the transform coding, discriminating the existence of the echo and defining (D) a false alarm zone in the high-energy parts of the digital audio signal, determining an initial processing and attenuating the echoes (E) in the parts complementary to the low-energy false alarm zone and inhibiting (F) the attenuation of echoes in the false alarm zone. The invention is applicable to the technology of coders/decoders in particular hierarchical coders/decoders.

Method for trained discrimination and attenuation of echoes of a digital signal in a decoder and corresponding device

The invention concerns an encoder for an input audio signal (S(z)) comprising a combination module combining the input audio signal with an intermediate counter-reaction signal forming a modified input signal and a quantification module scalable for the rate () of said modified input signal, delivering a binary raster of quantification indexes of a predetermined rate. This encoder is such that it comprises: a reverse quantification module () of a part of the quantification indexes of the binary raster corresponding to the indexes of a rate lower than the predetermined rate, for predetermining a reconstructed signal (S(z)), a module for determining () a quantification noise (Q(z)) derived from at least quantification modules and reverse quantification modules in series, a determination module () for a filtering function of the quantification noise from said reconstructed signal and a filtering module fit for applying () said filtering function to said quantification noise in order to obtain said intermediary counter-reaction signal. The invention also relates to an encoding method applied by the described encoder and a corresponding decoding method applied by a decoder.

Methods and apparatus for coding digital audio signals using a filtered quantizing noise

A method for generating mutually orthogonal signals having a controlled spectrum, includes the generation of a plurality of mutually orthogonal, controlled-power discrete spectra s(i) having dimension Q, i designating spectrum number. The aforementioned spectra represent time signals in the spectral range and have a modulus &#x3bc; that is constant in a spectral line designation set G and zero everywhere else. The method includes determining at least part of a complex Hadamard matrix H of order d=w in the case of spectra of real signals and d=2.w in the case of spectra of complex signals; determining the extension P of matrix H from G and dimension Q; and obtaining controlled-power spectra s(i)=&#x3bc;.P(H[.][i]), wherein H[.][i] designates the icolumn of matrix H. In addition, a plurality of mutually orthogonal time signals s(i) is also generated from the discrete complex signals.

Method for generating mutually orthogonal signals having a controlled spectrum

The linear predictive analysis method is used in order to determine the spectral parameters representing the spectral envelope of the audiofrequency signal. This method comprises q successive prediction stages, q being an integer greater than 1. At each prediction stage p(1.ltoreq.p.ltoreq.q), parameters are determined representing a predefined number Mp of linear prediction coefficients a.sub.1.sup.p, . . . , a.sub.Mp.sup.p of an input signal of the said stage. The audiofrequency signal to be analysed constitutes the input signal of the first stage. The input signal of a stage p+1 consists of the input signal of the stage p filtered with a filter with transfer function ##EQU1##

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Lannion, France

Alain Le Guyader