Abstract: A compact portable lectern device having a voice amplifier contained therein which may be easily placed upon a tabletop to provide a speaker's lectern and public address system. The device includes a cabinet case having a hinged panel which when swung open from the cabinet, forms the sloping shelf of the lectern. The hinged panel is provided with a pivotally mounted lever arm support member having its fulcrum laterally displaced and provides significant stability to the lectern shelf without the need of mechanical locks or fasteners. The device is additionally provided with a detachable microphone which may be conveniently stored with the cabinet during transport.

Abstract: An improved frequency sensitive circuit capable of adjusting one or more of its parameters in order to shunt an adjustable amount of electrical signal to a current sink, thereby controlling the amplitude of the signal. The frequency sensitive circuit is connected to the wiper of a potentiometer that is placed across the inputs of a difference amplifier in order to control the peak value of the cut or boost in the signal. The frequency sensitive circuit includes a shunt impedance connected between the wiper of the potentiometer and the current sink. A resonant circuit is connected to the impedance and is tuned to an adjustable resonant frequency. A compensation circuit, such as a difference amplifier referenced to the wiper, couples the output of the resonant circuit to the shunt impedance so that the impedance of the frequency sensitive circuit approaches infinity as the frequency of the electrical signal is displaced from the resonant frequency.

Abstract: This hands-free telephone prevents acoustic feedback between its speaker and microphone by attenuating either the transmission or receive path under the control of a corresponding pair of counters (computers), each counter sensing the signal divided and digitized from its corresponding path. An increase in counted pulses indicates feedback and causes a counter to more quickly reach a predetermined counter state (count), to trigger attenuation (damping) before it can be reset (restored) to zero by the other counter.

Abstract: A pitch and voiced/unvoiced detector comprising a low pass filter or variable cutoff frequency low pass filter for providing a constant power output, DC shifting and weighting circuits operating on the filtered analog signals, a summing circuit for the filtered and weighted signals, a peak detector with controlled exponential decay time and timing circuits which are used to distinguish pitch and voiced/unvoiced structure in the analog input signal.

Abstract: A six-telephone channel conference system features an all-digital CVSD (continuously variable slope delta modulation) conference bridge-like circuit. The delta modulation pulse train in each channel is transformed into a series of slope numbers which are processed by the conference circuit addition function to provide zero insertion loss, then by the subtraction function to provide 100% cancellation of a talker's voice to his ear. Transformation involves a sequential three-bit algorithm.

Abstract: The speech synthesizer minimizes storage requirements by storing basis functions each defining a waveform segment or phoneme within a pitch period and including formants F1 and F2, featuring readin at one rate and readout at different rates within the pitch period. The synthesizer is characterized by each basis function being represented by a data point plotted on a single line on a chart having first and second formant log-log axes and means for producing a speech waveform segment approximately representing any desired point located off of the single line on the chart by selecting and reading out of the memory one of the basis functions at a rate different than the basic storage rate.

Abstract: A telephone amplifier and attenuator circuit comprising an amplifier and an attenuator inserted in the transmit channel and an attenuator inserted in the receive channel of a telephone set. The speech signals conveyed by the transmit and receive channels are detected and added together for forming a sum control signal. The transmit amplifier is controlled by the detected transmit signal and the two attenuators are controlled in opposite directions by the sum control signal. In the preferred embodiment, the amplifier and attenuators are formed respectively by a balanced modulator and by balanced modulators inserted in the loop of negative feed back amplifiers.

Abstract: A device for electronically simulating vibrato, chorus, and pseudostereo effects and the radiation effects produced by a rotary loudspeaker with the aid of two loudspeakers or loudspeaker combinations, in which device a controllable amplifier is associated with each loudspeaker, the audio signal being applied to these amplifiers both directly and via a delay means, and both the delay and the gain of the amplifiers being varied synchronously by a subaudio-frequency generator.

Abstract: A hands-free telephone set has both transmit and receive channels open for the reception of signals, while still inhibiting feedback-singing. Two switched attenuators are provided in cascade in each channel. The first attenuator is switched after a syllable delay, and the second attenuator is switched after a yet longer delay.

Abstract: A method of determining the fundamental frequency or pitch period of a voice signal from a difference signal, formed with the aid of predictors, between the original voice signal and the voice signal estimated by the predictor. Only the significant characteristics of the difference signal are then auto-correlated and the maxima of the correlation coefficients determine the fundamental frequency or pitch period.

Abstract: In a speech recognition system of the type including a recognition unit responsive to a voice input and a conditioning input for recognizing the voice input to produce a recognition output, a start signal is produced whenever a voice input exceeds a threshold level and a pause interval detection signal is produced whenever a voice input falls below a threshold level. An output timing signal is produced when the detection signal lasts a preselected interval of time that may be either about 250 milliseconds or about 250 milliseconds plus a delay. The recognition output from the recognition unit produced in response to the detection signal is displayed in response also to the detection signal. The result is delivered to a utilization device in response to the output timing signal.

Abstract: Described herein are analog speech encoder and decoder systems using a plurality of narrow band pass filters with associated rectifiers and ripple filters for spectrum analyzing the speech or other suitable signals, and a corresponding plurality of narrow band pass filters with associated voltage controlled amplifiers for remaking the speech with either an injected carrier or a noise signal being applied to the voltage controlled amplifier inputs, said carrier or noise source signals being selected by a voice controlled circuit, activating the carrier in the presence of voiced sounds or vowels, and the noise source in the presence of unvoiced sounds or consonants; said innovations or the combination thereof consisting of (1) the use of a direct bypass for the high speech frequencies from the voice input to the decoder output, using a high pass filter essentially passing the unvoiced speech sounds, (2) the limitation of the bandpass filter range of the encoder and decoder sections to the cut-off frequency of t

Abstract: An audio squelch circuit uses spectral analysis of the audio signal to derive two test signals, one of the two indicating speech presence "energy" and the other "voiced" speech presence. The two test signals are logic-AND combined to decide speech presence and open the squelch gate. Detection of speech in the audio signal, composed of a voiced segment which is both preceded and followed by a non-voiced (consonant) segment, is improved by correspondingly lengthening the "voiced" test signal pulse with both earlier (anticipatory) initiation by a time interval "D," and with a later (prolonged) completion by a time interval "d".

Abstract: A frequency analyzer of a predetermined number of channels comprises a digital band-pass and a digital low-pass filter section. A preselected number of digital samples sampled with a sampling period are stored in a buffer memory to be read out in each sampling period. A band-pass parameter memory memorizes for the respective channels band-pass filter impulse responses, each having preselected values, equal in number to the preselected number. A band-pass filter calculator calculates a convolution of each read-out digital sample and the preselected values of each response. The low-pass filter section produces frequency analysis results for the respective channels in each analyzing frame period equal to a first prescribed number of the sampling periods.

Abstract: An audiometer that automatically produces test tones of predetermined duration whose frequency and level are changed in accordance with a programme. The persons being examined actuate a switch or the like each time that a test tone is perceived and the parameters of said test tone (frequency and level) are stored in a memory. Thus, evaluation becomes very simple. Furthermore, steps have been taken to measure the background level in the test room and to ensure that the test tone is repeated when the background level exceeds a maximum value during the time that the test tone is produced.

Abstract: A filter for reducing the effective keying passband of a VOX (voice operated relay) responsive to output signals comprising pulses which follow the peak frequency pattern of the audio input pulses includes a pair of retriggerable monostable multivibrators, a "D" type flip-flop circuit, and a NOR gate which produces positive output pulses used to trigger ON the voice operated transmitter only when the input signals occur within the specified passband.

Abstract: A telephone system for use by divers employing demand breathing apparatus. ounds picked up by each diver's microphone are processed by selective filtering, amplification, rectification and comparison to a reference voltage level to provide logic signals representative of presence or absence of inhalation noise that could mask voice transmissions of other divers or of a tender. The microphone output to listening stations is switched through an attenuation path by the logic signal representing inhalation noise and through a by-pass or full strength path by the other logic signal.

Abstract: A louspeaker system having a woofer, tweeter and crossover network has a closed box resonance of 81.5 Hz which frequency is above the half-power point of 65 Hz of the system that includes active equalization of the vented box woofer in the region below 81.5 Hz with an inexpensive two-pole one-transistor circuit.

Abstract: This invention concerns a method of, and apparatus for, reducing the ambient noise level at a location in the vicinity of a source of recurring noise. In its preferred embodiments the invention involves generating a series of cancelling noise signals which are exactly synchronized with the bursts of recurring noise from the source and adapting the cancelling signals in the series on the basis of the success achieved in nulling the noise from the source at the location.

Abstract: An amplifier for a telephone handset provided with standard telephone line cord having a pair of receiver input signal lines for direct connection to the handset receiver terminals and a pair of transmitter input lines for direct connection to the handset transmitter terminals. A printed circuit board is electrically connected to and secured to the handset receiver. The receiver input signal lines are directly connected to the printed circuit board without alteration. The input signal is received independently of the receiver input signal line polarity. The transmitter input lines are connected directly to the transmitter without alteration.