A first aspect of the present invention relates to a method for low-frequency emphasizing the spectrum of a sound
signal transformed in a
frequency domain and comprising transform coefficients grouped in a number of blocks, in which a maximum energy for one block is calculated and a position index of the block with maximum energy is determined, a factor is calculated for each block having a position index smaller than the position index of the block with maximum energy the calculated maximum energy and the energy of the block, and, for each block, a
gain determining from the factor is applied to the transform coefficients of the block. Another aspect of the invention is concerned with an HF coding method for coding, through a
bandwidth extension scheme, an HF
signal obtained from separation of a full-bandwidth sound
signal into the HF signal and a LF signal, in which an
estimation of the an HF
gain is calculated from LPC coefficients, the energy of the HF signal is calculated, the LF signal is processed to produce a synthesized version of the HF signal, the energy of the synthesized version of the HF signal is calculated, a ratio between the energy of the HF signal and the energy of the synthesized version of the HF signal is calculated and expressing as an HF
gain, and a difference between the
estimation of the HF gain and the HF gain is calculated to obtain a
gain correction. A third aspect of the invention is concerned with a method for producing from a decoded
target signal an overlap-add
target signal in a current frame coded according to a first coding mode. According to this method, the decoded
target signal of the current frame is windowed and a left portion of the window is skipped. A zero-input response of
a weighting filter of the previous frame coded according to a second coding mode is calculated and windowed so that the zero-input response has an amplitude monotonically decreasing to zero after a predetermined time period. Finally, the calculated zero-input response is added to the decoded target signal to reconstruct the overlap-add target signal.