In a telephone substation employing a dual tone multi-frequency signal generator, the common switch functions of disabling the transmitter and muting the receiver are performed by transistor devices responsive to a control signal produced by the signal generator. A bias voltage provided by the transistor device associated with the transmitter prevents dialing signals from reverse biasing the transistor device associated with the receiver and defeating receiver muting.

Disclosed audio signal recording methods and apparatus operate with a telephone set having a housing and a handset connected to a first modular jack in the housing via a handset cord having at an end thereof a first modular plug fitting into the first modular jack. For audio signal tapping purposes, there is provided a second modular plug fitting into the first modular jack, a second modular jack for receiving the first modular plug, and an electrical interconnection of the second modular jack w...

The presence of such signals is detected each time the following detection condition is satisfied, namely: that, for the duration of a predetermined "prior activity" period the amplitude of the signal on the telephone channel exceeds a threshold level while successive maximum values taken at short time intervals remain fairly constant in level. Apparatus for performing the method comprises a threshold level comparator (10) and a difference comparator (11) which control a detector (50) followed b...

A central control unit (scanner) is connected across a set of subscriber loops. At each subscriber's premises, an individual subscriber terminal unit (STU) is connected across that particular subscriber's loop. To each STU are connected the various instrumentalities which are to be monitored by the system, e.g. fire alarms, burglar alarms, etc. FSK modulated signals in the upper part of the audible range are transmitted from the scanner to the STUs at appropriate times. The STUs reply by means o...

A simplified combination of privacy circuit (U1) and holding circuit (U2) for use on a telephone subscriber loop (11). The circuit arrangement includes a diode array (31--34) within a conventional full wave rectifier bridge (21--24) having a pair of interchangeable terminals (28, 29) and a third differentiated terminal (39) for connection in the loop. The interchangeable terminals are connected in series with either the tip or ring conductor with the remaining terminal connected to the other con...

A transistor bridge rectifier circuit, which is capable of being monolithically integrated, is designed to connect the electronic circuits in a user's telephone set to a two-wire telephone line. The circuit includes a transistor bridge with a "Graetz bridge" circuit arrangement, a current generator, a pair of current mirror circuits connected thereto, which alternately conduct according to the polarity of the line, and a pair of controlled current gain transistors, each controlled by the output ...

In a hold circuit including a silicon controlled rectifier (SCR) normally turned on and connecting the hold circuit to a subscriber line, a first hold release circuit outputs a trigger signal to a transistor turning off the transistor and disconnecting a line seizing network. A second hold release circuit outputs a trigger signal to a second transistor responsive to the line seizing network being disconnected. The second transistor connects a load resistor across the SCR dropping the holding cur...

A reverberation apparatus includes a signal input terminal to be supplied with an input signal, an operational amplifier having an inverted input terminal, a non-inverted input terminal, and an output terminal. The inverted input terminal is connected to the signal input terminal through an input impedance circuit. The non-inverted input terminal is connected to a reference point, and the output terminal is connected to the reference point through an inductance circuit as a load and a first impe...

A music/speech filter is provided for automatically determining whether an audio signal is music or speech by obtaining a relative measure of the energy in a selective frequency range and, from this determination, controlling the passage or path of the audio signal. The filter can be attached to a radio receiver to selectively pass either music or speech at the option of the user.

This disclosure concerns an equalizer for an audio reproduction system in which equalization is achieved using a discrete time filter. The filter is preferably implemented with a microprocessor programmed for generating and storing the filter coefficients in accordance with a perceived acoustic test signal reproduced by the system. Following generation and storage of the coefficients, the microprocessor also serves to equalize an input audio signal by convolving the stored coefficients with digi...