Abstract: A hands-free telephone terminal includes a loudspeaker (HP), a microphone (MI) and loudspeaker gain control means (AUG, DIM, PP). A loudspeaker gain correction method cyclically determines a listening comfort index to deduce gain modification parameters. If the local user modifies the loudspeaker gain using the control means, the gain modification parameters weight the loudspeaker gain to optimize listening comfort during a telephone conversation for the local user and for the remote user.

Abstract: Several microphones (M1, M3) are arranged substantially in the same plane (P) and are distributed symmetrically with respect to a direction of symmetry (D) perpendicular to this plane (P). A phase shift is applied between the signals output respectively by different microphones (M1, M3) and the signals thus phase shifted are added, in such a way as substantially to cancel the signals relating to any sound wave arriving in phase and with the same intensity on each of the microphones (M1, M3).

Abstract: A differential encoder for speech encoding, typically in a 16 kHz wide band, has a self adaptive predictive filter, comprising a comparator receiving, on an additive input, successive samples of a signal to be encoded and, on a subtractive input, an estimated signal delivered by a prediction loop which receives the error signal from the output of the comparator, the prediction loop comprising a self-adaptive predictive filter, a gain control circuit and a multiplier which receives the outputs of the predictive filter and of the gain control circuit and whose output is connected to the subtractive input.

Abstract: A voice transcoder for use in compensating for sound distortions in helium speech, including a plurality of audio frequency channels, each defining a particular frequency band, the center frequencies of the channels being logarithmically spaced and frequency bands together covering the helium speech frequency band to be transcoded. Each channel comprises a band-pass filter coupled to a detector, a divider dividing band-pass filter by detector output to provide a signal having the frequency delivered from the band-pass filter at a standard amplitude, and a mutliplier multiplying divider output by another channel detector output to synthesize a part of the transcoded audio signal, the different parts of the transcoded signal being combined in an adder-subtracter. The said multiplier has one input coupled from divider output in the channel of rank i and the other input coupled from rectifier output in the channel of rank i + x, x being the same for any multiplier.

Abstract: A detection circuit for the significant peaks of a speech signal, comprising first and second detectors respectively for detecting the positive and negative peaks of said speech signal. Each of these detectors is followed by a peak charging circuit comprising a first integrator having a relatively large discharge time constant and a comparator comparing the detected speech signal and the output signal of said first integrator. Each peak charging circuit comprises in addition a second integrator having a relatively small time-constant. The discharge of the first integrator is effected up to a voltage equal to the output voltage of the second integrator, and the discharge of the second integrator is effected down to a voltage depending on the output voltage of the first integrator. The two integrators of each peak charging circuit provide a non-exponential decreasing signal which has an inflection point following a significant peak in the original speech signal.