Patent ID: 8831959

Claim:
A method in a transform audio encoder for encoding a time segment of an audio signal, the method comprising: deriving an indicator, z, of the position in a frequency scale of a residual vector of a segment of a transform vector associated with the time segment of the audio signal; deriving a measure, Φ, related to the amount of structure of the residual vector; determining whether a predefined criterion involving the measure Φ, the indicator z and a predefined threshold Θ, is fulfilled, thus estimating whether a change of sign of at least some of the non-zero coefficients of the residual vector would be audible after reconstruction of the audio signal time segment; wherein the predefined criterion is formulated as: ω 1 Φ+ω 2 z≦Θ(b), where ω 1 and ω 2 are scaling factors; and Θ is a threshold that depends on the bitrate b of the encoder; encoding the amplitude of the coefficients of the residual vector; and encoding the sign of the non-zero coefficients of the residual vector only when it is determined that the criterion is fulfilled, and thus that a change of sign would be audible.