An improved speakerphone (120 and 130 in FIG. 1) for radio and landline telephones is described. The improved speakerphone (120 and 130) includes a microphone (102 and 132), a speaker (104 and 134) and unique control circuitry (106 and 136). The control circuitry of speakerphone (200 in FIG. 2) interfaces a microphone (250) to a transmit signal (220) and speaker (260) to a receive signal (222) of a duplex communication path, such as a radio channel or telephone line. An audio switch (212) opens or closes the speaker audio path in response to a control signal (224) from control logic (230), and another audio switch (202) opens or closes the microphone audio path in response to the binary complement of the control signal (224). Transmit and receive signal detectors (206 and 207), each includes a logarithmic amplifier (240), an envelope detector (241), a smoothing filter (245 ), a valley detector (242), a summer (243) and a comparator (244) for detecting the presence of audio signals in environments that may be subject to high background noise. Binary output signals from the transmit and receive signal detectors (206 and 207) are applied to control logic (230) which generates the control signal (224) for opening and closing the transmit and receive audio paths. The control logic (230 in FIG. 3) includes delay circuitry (316 and 318) and logic circuitry (304, 306, 308, 310, 312 and 314) for setting and resetting a flip-flop (302) storing the control signal (224). The control logic (230) changes the state of the control signal flip-flop (302) for switching the audio path between the micorphone and speaker when audio signals from the presently closed audio path have not been detected for a time interval determined by the delay circuitry (316 and 318) and audio signals thereafter are detected on the other audio path.

Speakerphone for radio and landline telephones

A loudspeaking telephone system has a voice switch circuit in which voice signals on transmission and reception speech channels are respectively detected to produce control signals, and these control signals are compared to judge the levels of the voice signals on both the speech channels so that the switching between both the channels is effected under the control of loss of variable attenuators inserted in both the speech channels. The control signals corresponding to the voice signals on both the transmission and reception speech channels are converted through analog-to-digital conversion into digital values which are suitable for arithmetic operation. The arithmetic operation is such that the losses of the variable attenuators are automatically controlled in accordance with the use conditions of the loudspeaking telephone system to minimum values which can prevent the howling, transmitting blocking and receiving blocking.

Loudspeaking telephone system

A voice-switching device for use in a telephone terminal which applies an optimal amount of switched loss to a plurality of distinct receive transducers. The voice-switching device detects speech signals on the transmit and receive paths to determine a mode of operation. Based on the mode of operation the device applies optimal amount of loss to the transmit path and each output path separately. This system eliminates excessive attenuation of non-dominant receive transducers as well as optimizes the transition time from active to quiescent mode for all receive transducers.

Voice-switching device and method for multiple receivers

Apparatus and methods for automatically (i.e., without requiring manual user adjustment) reducing gain in one or both acoustic feedback paths of a cordless telephone when the handset and its base unit are operating in close proximity to one another, preventing uncontrolled feedback and audible howling even before it begins. A proximity detection module determines a distance between the handset and its base unit using an appropriate technique, e.g., using RSSI, round trip delay times, and/or GPS measurements. If the distance indicates that the handset is within close proximity to the base unit, appropriate attenuation of the microphone gain and/or speaker volume of the base unit and/or the handset will be implemented. One or more fixed levels of attenuation may be implemented based on a corresponding one or more measured close proximity distances between the handset and its base unit. Thus, the attenuation may result in a muting, a fixed amount of attenuation (e.g., 6 decibels (dB), 12 dB, or other appropriate fixed amount), or may be a variable amount dependent upon a relationship to the distance between the handset and the base unit.

Handset proximity muting

A circuit to improve noise mitigation and mode switching in telephony, wherein the noise-floor level is continuously estimated by comparing its stored current value to the signal level value and substituting the latter for the former if it is less than the former.

Noise mitigation and mode switching in communications terminals such as telephones

In the loudspeaking telephone circuit, the speech signal is used as a control signal for detecting the extent of decreasing the acoustic coupling between the loudspeaker and the microphone of the telephone set and of the coupling between the transmitting and receiving circuits of an anti-sidetone circuit from an expected worst condition for which the telephone circuit has been designed thereby automatically decreasing the value of the variable loss utilized for preventing howling by an amount corresponding to said decrease. This circuit provides satisfactory speech communication with a smaller loss inserted than a prior art voice switch thus greatly improving unnatural sound as caused by the voice switch.

Loudspeaking telephone circuit

In a voice switch circuit for use in a loudspeaking telephone circuit of the class comprising a main comparator for comparing the signal level of a receiving circuit with the signal level of a transmitting circuit, a transmitting variable loss circuit responsive to a condition wherein the signal level of the receiving circuit is higher than the signal level of the transmitting circuit for inserting a loss in the transmitting circuit thereby establishing a receiving condition, and a receiving variable loss circuit responsive to a condition wherein the signal level of the transmitting circuit is higher than the signal level of the receiving circuit for inserting a loss in the receiving circuit thereby establishing a transmitting condition, the voice switch circuit is constituted by a control variable loss circuit inserted between the receiving circuit and the main comparator, a second comparator for comparing the output signal level from the control variable loss circuit with the signal level of the transmitting circuit, and means connected between the second comparator and the control variable loss circuit for operating the control variable loss circuit under the receiving condition for decreasing the level difference between two inputs of the main comparator.

Ryoichi Matsuda

Papers

Loudspeaking telephone circuit

Voice switch circuits for use in loudspeaking telephone circuits

Sprachschalterkreis fuer eine lautsprecher-fernsprechschaltung