Abstract: A gain controller for normalizing signal levels from a plurality of remote stations connected to a teleconferencing bridge. Common monitoring circuitry is used to generate a clock signal, the duration of which is proportional to the magnitude of a test signal from the remote station. This clock signal in turn is stored in a separate binary counter, the output of which is used to individually control the amplifier gain in the channel connecting the remote station to the bridge.

Abstract: An improved equalizing system for modifying an input electrical signal representative of original sound so as to correct for the inherent nonflat frequency response of an audio signal processing apparatus and the acoustic effects of listening environment in which the loudspeaker system of the audio signal processing apparatus may be disposed. The improved equalizing system includes a comparator for comparing the signal energy in each of a plurality of select frequency bands of a predetermined frequency range of the input signal with that of the corresponding signal energy in a like plurality of bands of a like range of a second signal representative of the acoustic output of the loudspeaker system and as a function of the nonflat frequency response and the acoustic effects of the environment. A correction signal representative of the comparison is used to modify the energy within each band of the input signal so as to substantially correct for the nonflat response and the acoustic effects of the environment.

Abstract: A dual-tone multiple frequency signal generator is provided for use with telecommunications systems, data transfer systems and other applications. The tone encoding system utilizes MOS/LSI integrated circuitry on a single chip powered directly by telephone line voltages. An electronic keyboard circuit provides synchronized pulses to decode single-pole, single-throw keyboard switches by row and column. A crystal-controlled oscillator generates a reference frequency which is divided according to the row and column of an activated keyboard switch to obtain two pulse signals having frequencies representative of the activated switch. The outputs of the divider circuitry are fed to a programmed logic array which generates two digitally coded signals each representing a sinusoidal waveform. A digital-to-analog ladder network converts the digitally coded signals to continuous sine waves, and an operational amplifier combines the sinusoidal waveforms to provide a dual-tone output.

Abstract: This electronic ring sounder utilizes the loudspeaker and audio amplifier present in a speaker telephone to accomplish the bell sounding function. To this end, the amplifier is provided with a feedback circuit which, when enabled, causes the amplifier to oscillate in the audio frequency range. The feedback path includes a gate which is enabled in response to presence of the ring tone on the telephone line. Advantageously, the oscillation frequency is on the order of 1,000 Hz, and is gated on each half cycle of the ring signal. This produces a sound which closely simulates that of a conventional telephone bell.

Abstract: A universal acoustic coupler system includes a pair of flexible muffs for acoustically coupling a telephone handset to transducers (speaker/microphone) of an electronic input/output device. The muffs are formed of an external housing inside which an internal housing is positioned, defining a fluid insulator therebetween. The internal housing has a speaker/microphone cavity for receiving the input/output device speaker or microphone which opens into an earpiece/mouthpiece cavity for receiving the earpiece or mouthpiece of a telephone handset. The fluid insulator is formed to completely insulate the speaker or microphone to eliminate all external noise.

Abstract: Apparatus for remotely supervising via a telephone line a device includes a sensor for sensing for a telephone ring signal from the telephone line. In response to the sensing of the ring signal there is generated an off-hook condition which causes the termination of the ring signal. In addition an indicator responsive to the sensor produce a melody continuously repeated with an interval between each transmitted melody. This repeated melody is transmitted to the telephone line for counting by the caller. In addition, within the apparatus, a counter counts the melodies as they are produced. A key memory connected to the counter and responsive to the telephone line is activated when a predetermined count has been counted by the counter and there is a voice signal on the line from the caller. The operation of this key memory alerts a control circuit for the reception of subsequent voice signals which permit the changing of state of a controlled device.

Abstract: A solid state subscriber station network which provides transmitting, receiving and regulating functions using a single active element. The transmitted signals, the received signals and the regulatory functions can be separately varied within proscribed limits without adversely affecting the other functions.

Abstract: An improved telephone station set for use with a switching system which senses flashing is disclosed. A separate flash key is included on the set. Depression of the flash key causes decoupling of the set for a predetermined time which corresponds to the flash window. Depression of the hook switch, assures decoupling of the set for a sufficiently long period of time so that a hang-up is detected even if the hook switch is immediately released.

Abstract: A DTMF signal receiver, for telephone systems, includes an amplifier with automatic gain control for receiving and amplifying DTMF and audio signals. A series of bandpass and notch filters receive the output from the amplifier for producing bandpass and notch outputs in response to the DTMF frequencies. A detector receives the bandpass output from each of the filters to produce a signal representing the presence or absence of a signal of each DTMF frequency in the amplifier output, and a DTMF decoder receives the signals from all such detectors and produces output signals in response to simultaneous detection of preselected pairs of DTMF frequencies. A voice guard circuit receives the notch output from the last filter in the series and compares the amplitude of that notch output with a threshold level to produce a disable signal whenever the amplitude of the notch output is greater than the threshold.

Abstract: A throat microphone consists of a dynamic pressure transducer sealed within an airtight tympanic enclosure to be held by an elastic band on the user's throat near the voice box. The electrical signals generated by the transducer are applied as an input signal to an amplifier and speaker unit where the signal is conditioned by a preamplifier stage for further amplification by a second stage that contains a variable reactive negative feedback network that acts as a low pass filter and corrects the phase shift of the different lower frequency audio signal components while emphasizing the higher frequency components so that severe phase distortion of the signal applied to the drive speaker through an output power amplifier stage can be minimized to make the speech sounds reproduced more intelligible.

Abstract: A bias control circuit adapted to be utilized with complementary, tracking current sources for use in an audio reproduction system including volume and tone control circuits to optimize the signal to noise ratio of the system at maximum gain without compromising the signal handling capabilities of the system. The bias control circuit includes an interface circuit responsive to an applied volume control signal for varying a bias signal connected to the output of the interface circuit. A second and third circuit are coupled with the output of the interface circuit which are responsive to the bias signal for deriving, respectively, a volume output signal to control the gain of the volume control circuit and a current biasing signal for controlling the bias levels of the tone control circuits. The current biasing signal varys proportionally with increases in the volume control signal from a first level to a second level remaining constant thereafter.

Abstract: A directional array of acoustic transducers is disclosed. The acoustic transducers are arranged colinearly and in pairs symmetrically about a center line of the directional array. The distances of the acoustic transducers on either side of the center line of the array are neither linear nor monotonic. These distances are calculated using a recursive far field response formula which effectively reduces sidelobe magnitudes to a desired design amplitude envelope. The response produced is highly directional, comprising one main lobe and a plurality of sidelobes each less than the desired design envelope, which is substantially lower than the main lobe but of arbitrary (e.g., stepped) shape.

Abstract: Some cellular mobile radiotelephone systems use tones for certain call connection supervisory functions on radio links. The presence of the correct tone in a received radio channel call signal is determined by using the received signal for producing (32) a lower frequency tone that is readily selectable (36) from similar tones produced in response to incorrect supervisory tones. Circuits are also shown for separately processing received call signals to produce (41, 53) supervisory tone phase information that is indicative of range between communicating stations. Several circuits (72; 40 and 46; 59-62) are shown for enhancing the accuracy of the produced phase information of the correct tone.

Abstract: An electronic tone ringer for use in telephone substations. This circuit operates in response to conventional ringing signals and generates a single tone alert signal interrupted at a low frequency. The audible tone alert signal is generated by a piezo-ceramic transducer.

Abstract: An improved loudspeaking substation circuit employing a dual-tone multi-frequency signal generator wherein output tone levels are regulated by the substation transmission circuit when operating in either a loudspeaker or handset mode. The circuit further provides for preventing acoustic feedback and self-oscillation between the loudspeaker and handset transmitter while transferring between either mode.

Abstract: A device for electronically modulating a musical tone signal to produce substantially the radiation effects produced by a rotary loudspeaker with the aid of two loudspeakers, in which circuit an amplitude modulator is associated with one loudspeaker and a variable delay device is associated with the other loudspeaker, the musical tone signal being applied to both the amplitude modulator and the variable delay device, and both the variable delay device and the amplitude modulator being modulated synchronously by a sub-audio frequency modulating signal.

Abstract: A mobile telephone communication system is provided with a plurality of mobile units having a transmitter-receiver capable of being tuned to a plurality of radio channels. A plurality of base stations are provided with receivers capable of detecting carrier level drop-off and a control station is operable to command the given base station to transmit an instruction to the mobile unit commanding it to transmit its signal over a channel which is common to all of the base stations. The control station is then operable to detect an increased carrier level in a zone corresponding to a second base station, and to instruct each of the base stations to transmit a signal over the common channel commanding the mobile unit to switch channels to an idle channel corresponding to a second base station.

Abstract: A device for electronically simulating vibrato and tremulant effects and the radiation effects produced by a rotary loudspeaker with the aid of two loudspeakers, in which a musical tone signal is applied to a variable delay device associated with one of the loudspeakers. The frequency modulated signal produced by the variable delay device is also subjected to amplitude modulation, controlled in synchronism with the variable delay device, and the resulting composite signal applied to the other loudspeaker. Additionally, the high frequency components of the frequency modulated signal from the variable delay device are summed, in and out of phase relationship, with the composite amplitude modulated signal to simulate the effect of a rotating high frequency horn radiator.

Abstract: A communication device coupled to a standard telephone which has an alphanumeric rotary dial or pushbutton keyboard. A simple, easily-learned code (11) is utilized which can be transmitted over telephone lines (14) using the rotary or push-button digits (10). To communicate, the called party enters the appropriate position for the letter of the alphabet to be communicated. A second entry identifies which one of the plurality of letters (or the number) is intended to be transmitted. The calling party has apparatus (18, 20) attached to the telephone set (16) which decodes the two-digit coded entry, and converts the two-digit code to a standard machine-readable format which can be displayed on a standard output device (26) such as an alphanumeric display or, for blind persons, a braille or similar output device. The calling party can transmit a message to the called party, by keying characters into a keyboard (22).

Abstract: An automatic volume control system comprises a source for producing an audio signal; an amplifier responsive to a control signal for varying the amplitude of the audio signal, a transducer for converting the audio signal to sound energy, a detector for detecting the output of the transducer and ambient noise which interferes with comprehension of the sound energy, and a phase comparator connected to the detector and to the audio signal source for comparing the phases of the outputs thereof and for producing an output proportional to the level of detected ambient noise. The output of the phase comparator is connected as a control signal to the amplifier means so as to control the amplitude of the audio signal.