System for optimising the sound rendition of low frequencies of a signal composed of a left-hand channel and a right-hand channel, including means for varying a plurality of parameters (P 1, P 2, P 3,... P N) of said audio signal, according to the volume pitch (V 1, V 2,..., V P) of said audio signal selected by a user, in particular filtering and compression parameters and parameters related to the harmonics of said audio signal, by seeking to optimise the dynamic range and the bandwidth of said audio signal according to the volume, in order to provide an optimum rendition for the user, said means for varying a plurality of parameters (P 1, P 2, P 3,... P N) of said audio signal including: - a first delay module receiving the audio signal as an input; - a harmoniser receiving the audio signal as an input and including a pre-harmonics filter of the IIR type connected to a harmonics generator connected to a post-harmonics filter of the IIR type; - a dry-gain module at the output of the delay module; - a wet-gain module at the output of the harmoniser; - a crossover module receiving as an input a combination of the outputs of the dry-gain and wet-gain modules, said crossover module being composed of a submodule known as a "crossover high" module of the IIR type and a submodule known as a "crossover low" module of the IIR type; - a second delay module at the output of the crossover module; - a compression block at the output of the crossover module, said compression block including a so-called speaker cut submodule, consisting of a bi-quad filter and a stereo compressor having adjustable parameters such as the threshold, the compression slope, the expansion slope, the attack time, the release time and the gain compensation; - a bass front gain module at the output of the compression block; - a bass rear gain module at the output of the compression block; and in that an output signal is composed of a left front channel and a right front channel corresponding to a combination of the output signals of the bass front gain module and of the second delay module, and a left rear channel and a right rear channel corresponding to a combination of the output signals of the bass rear gain module of the second delay module. - a first delay module receiving the audio signal as an input; - a harmoniser receiving the audio signal as an input and including a pre-harmonics filter of the IIR type connected to a harmonics generator connected to a post-harmonics filter of the IIR type; - a dry-gain module at the output of the delay module; - a wet-gain module at the output of the harmoniser; - a crossover module receiving as an input a combination of the outputs of the dry-gain and wet-gain modules, said crossover module being composed of a submodule known as a "crossover high" module of the IIR type and a submodule known as a "crossover low" module of the IIR type; - a second delay module at the output of the crossover module; - a compression block at the output of the crossover module, said compression block including a so-called speaker cut submodule, consisting of a bi-quad filter and a stereo compressor having adjustable parameters such as the threshold, the compression slope, the expansion slope, the attack time, the release time and the gain compensation; - a bass front gain module at the output of the compression block; - a bass rear gain module at the output of the compression block;