An arrangement for generating an electrical audio signal in response to a sound signal applied to a microphone in a reverberating room removes the reverberations with an adaptive filter. The filter learns or adapts so as to cancel the room echoes by receiving both the audio signal affected by reverberation and a clean audio signal from a highly directional local-acting microphone placed near the source of the sound. The signal to be filtered is applied to a transversal filter including a tapped delay line having variable taps or multipliers to produce incrementally delayed multiplied samples. The multiplied samples are summed, and the sum signal is subtracted from the clean signal to produce a difference signal. A .mu.P is programmed to iteratively calculate the effects of changes to the tap values and to select tap values which tend to reduce the magnitude of the difference signal. When the filter is converged, the difference signal is near zero. At this time, the filtered signal and the clean signal are similar, and therefore the filter characteristic removes the effect of reverberation. The tap values are then fixed, and the signal with room reverberations can be made clean by the adapted filter.

A voice-controlled hands-free facility contains a microphone, an internal and an external loudspeaker, and two series combinations of an input amplifier (EV), a variable attenuator (DR), and an output amplifier (AV), one for the send path and one for the receive path, and is controlled by a voice control unit (SS) connected to the output (E) of the input amplifier (EV), to the output (D) of the variable attenuator (DR), and, by a line (L), to an input of the variable attenuator (DR). To permit the hands-free facility to be switched from a single-part mode of operation to a two-part mode, the output (E) of the input amplifier (EV) in the send path and/or the receive path is connected to the output (A) of the output amplifiers (AV) through a bypass device (BP) and a switching unit (T).

A telephone includes a speech network for transmitting an outgoing voice signal and receiving an incoming voice signal from a remote telephone. The speech network is not supplied with power from a telephone exchange through a telephone line but supplied with a separate power supply. To interrupt the power supply from the telephone exchange, a transformer is interposed between the speech network and the telephone line. A ringer circuit and a dialer circuit are connected to the primary side of the transformer. Because the power supplied to the speech network does not fluctuate, the circuit design of the speech network can be readily performed using inexpensive circuit components.

A telephone set which has a hands-free mode of operation is disclosed. The telephone set includes a telephone circuit connector to a handset and a hands-free circuit connected to a loudspeaker. A hook switch is mechanically operated in accordance with operation of the handset. A semiconductor switch is connected in parallel with the hook switch and is controlled by a control circuit. The telephone circuit or hands-free circuit is selectively connected to a pair of telephone lines through the hook switch or the semiconductor switch.

A method for electronically simulating a cradle switch and a hands free talking-loudspeaking key in a telephone station. The cradle switch and hands free talking-loudspeaking key must be functionally coupled to one another in such a telephone station. This is generally effected mechanically. Structural difficulties and an operator-unfriendly arrangement of the key have thus resulted. To solve these problems, a control pulse generator is provided which, by an appropriate emission of control pulses following the actuation of the key and/or the cradle switch, triggers the individual functions in the participating assemblies of the telephone station. In the rest state, the control pulse generator and a dialing store of the keyboard are maintained on standby by a weak, line-fed standby current supply. The method is suitable for all hands free talking-loudspeaking telephone stations.