In a loudspeaking telephone arrangement, there are separate channels for outgoing speech (A-Tx) and incoming speech (A-Rx), and the channels are sampled at intervals. The results of these samplings, which represent the amplitudes of the speech in those channels are each compared by a microprocessor with a preset threshold. The background noise level is also sampled and the result used to adjust the speech channel threshold. Each channel has an attenuator, and that is adjusted so that attenuation is reduced in the presence of speech and increased in the absence thereof. The adjustment on the basis of background noise enables the current state of the channels to be taken into account.
A digital echo suppression circuit in a four-wire digital telephony circuit having an echo from a local or remote connection to a two-wire circuit or other echo source. The invention incorporates a simple method of using the sample pairs from the first and second sampling circuit to produce a control signal from a control circuit. If the subscriber signal is "louder" than the network signal, then the subscriber signal is passed through. If the network signal is louder than the subscriber signal, the interrupter is activated and a zero level is substituted for the subscriber signal in transmissions toward the network. The invention uses the scheme of comparing instantaneous signal amplitude and using the larger amplitude to set a threshold value. The signal setting the threshold then remains the "loudest" until such time as the other signal can exceed the threshold. The threshold is slowly decremented, but the original signal may refresh the threshold to a higher level if a new peak value replaces the old threshold value with the new peak value. The identity of the input network or subscriber producing the threshold is stored. If the current threshold is the result of a network signal, the interrupter is activated and echo is suppressed. If the current threshold is the result of a network signal, the interrupter is activated and echo is suppressed. If the current threshold is the result of a subscriber signal sample, then the interrupter is deactivated and subscriber signals are transmitted onward toward the network.
A mobile radiotelephone (120) includes a microcomputer (220), speakerphone control circuitry (106) and mobile radio (112). Mobile radio (112) includes a transmitter (242), receiver (244) and a duplexer (243) for coupling the transmitter (242) and receiver (243) to the mobile antenna. In the transmit voice path, speakerphone control circuitry (106) includes switch (201), variable gain amplifier (202), compressor amplifier (203), switch (204), variable gain amplifier (205), and two registers (212-213). In the receive voice path, speakerphone control circuitry (106) includes variable gain amplifier (232), expander amplifier (233), switch (234), variable gain amplifier (235), switch (236) and two registers (216-217). Speakerphone control circuitry (106) also includes rectifier/filter (224), a companding analog-to-digital (A/D) converter (225), two latches (218-219), rectifier/filter (226) and two registers (214-215). Microcomputer (220) accesses registers (212-217) by means of a data bus (222) including address, control and data lines. Microcomputer (220) utilizes digital samples from A/D converter (225) to continuously generate and store in its memory an envelope signal and a valley signal for the transmit and receive voice paths. In order to determine when to switch gain between the voice paths, microcomputer (220) compares the envelope signal to the valley signal to detect the presence of voice signals and, if the voice signals are detected for a pre-selected time, the gain of the path in which voice signals have been detected is increased and the gain of the other path is decreased.
A single integrated circuit forms a hands-free telephone unit for use in a digital telephone network and in association with an external keypad, an external microprocessor, an external microphone, and an external speaker. The integrated circuit includes a keypad monitor arranged to provide digital key code signals, an audio processor for supporting hands-free operation, and a digital interface to provide a digital interface between the integrated circuit and the digital network and the external microprocessor.
Device for performing the "hands-free" function in a telephone set associating the gain switching and echo cancellation functions. This device is characterized in that it comprises a gain switch and an echo canceller, said switch having in the emission and reception channels a circuit for measuring the amplitude of the signals present on these channels, a checking circuit for determining the state of the telephone set (emission, reception, rest,) a calculating member controlled by the checking circuit, variable attenuators controlled by the calculating member, said calculating member evaluating, as a function of the relative amplitudes of the signals in emission and in reception, the echo cancellation performances obtained by the device and adjusting as a function thereof the variable attenuators in each channel, so that the overall attenuation in the loop always assumes the minimum value ensuring the stability of the system.
An improved switched-loss, adaptive speakerphone dynamically adjusts its switching thresholds and other performance parameters based on an analysis of acoustic environment and telephone line conditions. To access these conditions, the speakerphone utilizes a computer with associated firmware. As part of a calibration process, the speakerphone computes its thresholds before each use to compensate for possible variations in hardware circuitry therein. This is achieved by passing a first and then a second level of a test tone signal through the hardware circuitry and measuring the resulting response. The speakerphone also measures the acoustics of the room in which it operates as part of the calibration process. For this measurement, a tone burst signal is generated through a loudspeaker in the speakerphone and measured by a microphone also in the speakerphone. A time-domain acoustic response of the room is obtained which provides to the computer the amplitude of the return signal and the duration of its echo. The calibration process is also applied to the speakerphone's interface to the telephone line through a hybrid. While in use, the degree of hybrid reflection is measured and the result provided to the computer. With the information on both the acoustic environment and the hybrid, the adaptive speakerphone is able to adjust on a real time basis the amount of switched loss and threshold switching levels between operating states to suit existing conditions. If, for example, the speakerphone is attached to a good telephone line and is in a good acoustic environment, it will provide the user with near full to full duplex performance.
