Loudspeaker gain correction for a hands-free telephone terminal

Details Loudspeaker gain correction for a hands-free telephone terminal Loudspeaker gain correction for a hands-free telephone terminal

1997-08-27

1999-10-19

Isen, Forester W.

Telephonic communications

Substation or terminal circuitry

For loudspeaking terminal

379202, 379390, 379406, 379409, 379420, H04M 900

Patent

active

059701374

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention concerns a loudspeaker gain correction method for a "hands-free" telephone terminal or for an audioconference telephone terminal.
2. Description of the Prior Art
A hands-free telephone set or telephone terminal includes a sound pick-up device with one or more microphones, a sound output device with one or more loudspeakers and transmit and receive signal processing circuits. These circuits include an acoustic echo canceller, an electric echo canceller and a gain variation device for attenuating the signals transmitted during a telephone conversation to prevent the Larsen effect. The attenuation is determined by the dominant transmission direction and by the performance of the echo cancellers.
A user controls the listening level by modifying the loudspeaker gain. The higher the chosen listening level, the less attenuation is applied to the non-dominant transmission direction. This attenuation is called the stability gain and takes a positive value less than unity. An excessively high attenuation, for example greater than 10 dB, would make listening more uncomfortable for the local user and for the other party, called as a remote user. The latter perceive variations in the levels of the speech signals transmitted and have the sensation of a half-duplex communication. When choosing the listening level, the local user is most sensitive to the sound intensity of the voice of the remote user and chooses an excessively high listening level. Unknown to them, this then causes a deterioration of the overall quality of the audioconference, in particular through a progressively more accentuated sensation of half-duplex communication. This sensation is all the stronger for the remote user if he is using the handset of his telephone.


OBJECT OF THE INVENTION

The object of this invention is to provide a loudspeaker gain correction method for optimizing listening comfort during a telephone conversation, not only for the local user but also for the remote user.


SUMMARY OF THE INVENTION

Accordingly, a method of loudspeaker gain correction in a hands-free 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 the loudspeaker gain, the transmit and receive channels being served by a telephone line, is characterized in that it comprises 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 the product of the measured transmit signal by the transmit compression gain is between two predetermined thresholds and the product of the measured receive signal by the receive compression gain is between two other predetermined thresholds,
measuring an output signal of the microphone on the transmit channel and an input signal of the loudspeaker on the receive channel,
comparing the measured microphone output signal and the measured loudspeaker input signal to determine an acoustic echo path gain between the loudspeaker and the microphone,
determining a stability gain as a function of the transmit compression gain, receive compression gain, acoustic echo path gain and loudspeaker gain,
determining a listening comfort index as a function of the stability gain and the listening comfort index of the preceding cycle,
comparing the listening comfort index with predetermined thresholds,
selecting two of the predetermined thresholds bracketing the listening comfort index and defining a range of variation of the listening comfort index with which are associated gain modification parameters, and
modifying the loudspeaker gain controlled by the gain control means with the loudspeaker gain weighted by the modification parameters.
The method of the invention matches the loudspeaker gain modifications commanded by the user to the listening comfort so that a gain modification does not deterior

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