| 摘要 |
In a device for improving the side tone suppression or loop gain in intercom systems, it is proposed to leave the propagation constant constant in the low-frequency transmission range and to carry out voice-level-dependent control of the gain in the low-frequency range with distinction between simplex and duplex speaking, the sum of the gains remaining constant in the transmitting and receiving direction. Alternatively or as a supplementary measure, the method of an (adaptive) echo cancellation, which is known per se, can be used for achieving adequate loop gain in the low-frequency range. Finally, it is possible to control the pass-bands and stop-bands of the band filters involved speaker-dependently over the entire transmission range in such a manner that in the case of pure duplex speaking, the signal of the transmitting subscriber is transmitted unfiltered and the signal on the other party is attenuated by the amount of the desired increase in loop gain, whilst, in the case of simplex speaking, the gains of the individual band-pass systems are controlled in dependence on the respective voice level, in such a manner that the stop-bands of the filter transfer functions of the louder speaker in each case are attenuated less and the pass-bands of the inverse filter transfer functions of the quieter speaker are correspondingly attenuated more.
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