Loudspeaker gain correction for a hands-free telephone terminal

A method of loudspeaker gain correction in a hands-free telephone terminal,

• said telephone terminal having a loudspeaker at the output of a receive channel and a microphone at the input of a transmit channel, and gain control means for commanding modifications of a loudspeaker gain, the transmit and receive channels being served by a telephone line,
• said method comprising the cyclic steps of:
• measuring a transmit signal on the transmit channel and a receive signal on the receive channel,
• determining a transmit compression gain and a receive compression gain respectively so that a product of the measured transmit signal by said transmit compression gain lies between two predetermined thresholds and a product of the measured receive signal by said receive compression gain lies between two other predetermined thresholds,
• measuring an output signal of said microphone on said transmit channel and an input signal of said loudspeaker on said receive channel,
• comparing the measured microphone output signal and the measured loudspeaker input signal to determine an acoustic echo path gain between said loudspeaker and said microphone,
• determining a stability gain as a function of said transmit compression gain, receive compression gain, acoustic echo path gain and loudspeaker gain,
• determining a listening comfort index as a function of said stability gain and the listening comfort index of a preceding cycle,
• comparing said listening comfort index with predetermined index thresholds,
• selecting two of the predetermined index thresholds bracketing said listening comfort index and defining a range of variation of said listening comfort index with which gain modification parameters are associated, and
• modifying the loudspeaker gain controlled by said gain control means by weighting the loudspeaker gain by said gain modification parameters.