Showing papers on "Audio signal processing published in 1974"

Broadcast signal identification system

Abstract: A process for automatic electronic recognition and identification of programs and commercial advertisements broadcast on television and radio wherein a digitally sampled reference signal segment derived from either the audio or video portion of the original program content to be identified is compared with successive digitally sampled segments of the corresonding audio or video portion of a broadcast signal in a correlation process to produce a correlation function signal. The sampling rates and the time duration of the reference signal segment and the broadcast signal segments are the same. When the signal segments which are compared are the same, the correlation function signal is relatively large and a recognition thereof is achieved when such correlation function signal exceeds a selected threshold level. The compared signal segments may also be obtained as low frequency signals derived from the original reference and broadcast signals by non-linear and envelope formation processing techniques.

Video system for conveying digital and analog information

Abstract: A video system having a transmitter in which a composite signal is formed by combining digital information with scanlines of an analog video signal generated by a line scanning device, and a receiver in which the digital information is recovered. The digital information is combined with the analog video signal at predetermined locations along scanlines of the video signal, and these predetermined locations are varied in order to prevent visible deterioration of the video image. In the video receiver, the digital information is recovered by examining the composite signal at the predetermined locations to extract the digital information. Each bit of digital information to be conveyed is represented by a first pseudo-random digital pulse sequence (or its complement, depending on whether the data bit is 1 or 0) which is superimposed on a selected scanline of the analog video signal to form the composite signal. The digital information is recovered at the receiver by generating a second pseudo-random digital pulse sequence in synchronism with the first sequence, and by examining the composite signal at locations determined by the second digital pulse sequence to extract the digital information contained in the composite signal.

Emergency radio frequency warning device

Abstract: An electronic whistle in the form of broad band radio frequency interference generator. A broad band generator generates a coherent or random noise signal which is modulated by an audio signal which corresponds to an audible warning signal such as a whistle or a siren. The modulated signal is then utilized to modulate a carrier signal and amplified and transmitted so that the radios in vehicles in the immediate area will receive an audible interference signal regardless of the particular channel to which the radio is tuned. The audible interference signal may be an intelligible reproduction of the input audio signal so that the driver of the vehicle can determine whether the warning signal is generated by a train whistle, a siren or a human voice.

Method and apparatus for reducing noise content in audio signals

Abstract: Unwanted background noise in audio signals, and particularly in musical material, is significantly reduced by a multiple band dynamic filtering system operated in response to the fundamental and harmonic content and degree of correlation or nonrandomness of the audio signal. A plurality of voltage controlled band-pass gates or filters are established in the audio signal path for individually and selectively passing frequency content of the audio signal falling within each frequency band. The fundamental and harmonic content of the signal, typically a musical composition, is detected by a corresponding plurality of band-pass signal detectors, the outputs of which are connected to and for operating associated band-pass gates. Normally the band-pass gates are closed blocking any background noise present on the incoming signal. The band-pass detectors sense the presence of any fundamental or harmonic signal content and cause the appropriate band-pass gates to open and pass the full frequency content of the musical signal. The degree of correlation or nonrandomness of the audio signal is automatically monitored and the threshold detection of the presence of signal content in any one of the given frequency bands is varied in accordance with the degree of signal correlation.

Digital storage system for high frequency signals

Abstract: A system and a method are provided for storing high frequency signals, for example microwave signals, for later reproduction with any desired degree of fidelity. The system and method involve determining a measure of the phase difference between an incoming high frequency signal and a converting signal. The measure of the phase difference consists of a plurality of signals which may change rapidly. The phase difference signals are converted to digital frequencies and may be stored or transmitted in that form. Later, the digital signals may be converted to analog signals (if necessary) and used to control the phase of a signal having the frequency of the converting signal. This process reconstructs the incoming high frequency signal.

Secure television system

Abstract: A secure system for television transmission wherein a television signal is transmitted on one frequency channel and a composite high fidelity stereophonic audio signal is transmitted on a separate unrelated frequency channel. Unauthorized reception of the audio portion of the signal is prevented by using non-standard multiplex transmission and by transmitting the audio signal in a frequency band which is preferably non-receivable by a standard television or FM receiver.

Signal editing and processing apparatus

Abstract: A signal editing and processing technique for converting a plurality of continuous signals, especially long term continuous audio signals respectively relating to short term still picture signals, to a transmitting signal in which signal transmission periods and pause periods are provided, having an integer ratio of time duration with each other, wherein other signals, especially the picture signals, should be transmitted. All continuous signals are sequentially converted to digital signals addressed in accordance with relevant continuous signals, and once stored in arbitrary positions of a memory, and then read out in a given multiplexed sequence corresponding to the transmission periods of the transmitting signal. The read out multiplexed digital signals are sequentially stored in another memory, and then read out with a given high speed equal to that of the signal transmission. The digital signals read out with the high speed are stored in still another memory, and then read out repeatedly to form the transmitting signal.

Safety means for audio speakers

Abstract: Overload protection circuitry prevents burn out of speakers resulting from an overload due to wattage exceeding the audio speaker or audio speakers capacity. A relay is adapted to automatically disconnect the audio speaker or audio speakers from an audio amplifier''s output signal and connect a substitute load across the audio amplifier''s output. This relay is adapted to automatically reconnect the audio speaker or audio speakers and disconnect the said substitute load when the audio amplifier''s output signal or output wattage again drops to a safe level.

Readback circuits for digital signal recorders

Abstract: Digital signal processing techniques enhance readback of digital signals from a magnetic recorder. Sampled signal amplitudes obtained at bit period boundaries and midpoints are converted to digital signal sets, which sets are processed for equalization, DC restoration, phase error detection, generation of timing signals, and amplitude compensation of the sampled signal amplitudes.

Predictive conversion between self-correlated analog signal and corresponding digital signal according to digital companded delta modulation

Abstract: A predictive analog-to-digital converter for converting a selfcorrelated analog signal into a delta modulated digital signal according to companded delta modulation comprises a digital step size signal generator responsive to the digital signal for producing a digital step size signal variable to represent at least three step sizes for successive quantization of the selfcorrelated analog signal, a memory for memorizing a digital sum signal supplied thereto and for producing the memorized digital signal, an adder for deriving the algebraic sum of the memorized digital signal and the digital step size signal to produce the digital sum signal to be newly supplied to the memory, and a local digital-to-analog converter for converting the memorized digital signal into the predicted analog signal for use in comparison with the self-correlated analog signal in accordance with the predictive conversion technique.

Method and apparatus for mixing and recording multi-track stereo audio signals which have been recorded as several individual audio signals

Abstract: A method of and apparatus for mixing and recording multitrack stereo audio signals from individual audio signals while utilizing the development of analog signals which are indicative of level, etc., converting the signals to digital form for clock controlled processing and reconverting to analog form to actuate mixing control elements.

Dual tone multiple frequency receiver/decoder

Abstract: A method and apparatus for separating the two analog component signals which make up a dual tone multiple frequency (Touch Tone) signal, converting the component signals into digital identification signals representative of the component signals, and then recombining the identification signals and developing a digital output signal which corresponds to the particular input signal. The apparatus includes signal separating means for separating the input analog signal into its two component signals, frequency identification decoding means for identifying the two component signals and developing digital identification signals corresponding thereto, and digital logic means responsive to the identification signals and operative to develop particular one-of-sixteen digital output signals which correspond to the particular Touch Tone signal input to the system.

Circuit for curtailing effects of bit errors in pulse coded transmission

Abstract: A differentially pulse coded digital representation of a continuous analog signal is digitally accumulated, and each time polarity information indicates that the accumulated digital approximation changes sign the digital representation is complemented. The result of this action is that each bit of a predetermined type in the digital representation, and following the complementing point in a signal flow sense, has the same directional effect, on the digital accumulation, with respect to a predetermined signal reference level within the range of the continuous analog signal variation. Several embodiments are shown with different types of digital accumulation and different circuit locations for realizing the inversion of the digital representation.

Audio processor circuit for an fm-stereo radio receiver

Abstract: An audio processor is disclosed which includes circuitry for modifying pure left and right audio signals by blending the left audio signal with the right audio signal as a function of frequency and for rolling off the higher frequencies of the blended signal. The processor further includes circuitry for selecting complementary portions of a blended, rolled-off audio signal and a pure audio signal as a function of the RF carrier strength to improve the overall listenability of the audio.

Method and system for transmitting signals from a selected one of a plurality of video sources in a central apparatus room and the associated audio and control signals to at least one television studio

Abstract: At least one television studio is to receive video signals from a selected video source and the associated audio and remote control signals, where the video and associated signals are each furnished by one of a plurality of signal sources located in a central apparatus room. The DC remote control signals are converted into audio frequency signals and are multiplexed with the corresponding audio signals. In one embodiment of the invention, each video signal source is connected to one input of a switching matrix whose output is connected to the television studio, the switching matrix being externally operable to connect the selected input to the output. A second switching matrix has a plurality of inputs each receiving one of the multiplexer signals and also an output connected to the television studio, the second switching matrix being selectively operable to connect the multiplexer signal corresponding to the selected video signal to the output. In a second embodiment, the multiplexed audio signal is first modulated onto a carrier signal having a frequency outside of the video signal frequency band. A modulated signal is then combined with the video signal and the so-combined signal is applied to one of a plurality of inputs of a single switching matrix whose output is connected to the television studio.

Audio-visual apparatus with control signal operated gating means

Abstract: Adaptor for reliably switching between audio and video information signals obtained from an external audio input device (e.g., the tape of a standard audio cassette recorder or player) with only the video information signals being applied to standard television receiver.

Audio frequency phase modulator in hearing test system

Abstract: Disclosed is a test system primarily designed for free field testing of the hearing of an individual utilizing phase modulation to reduce or eliminate the production of standing waves thereby permitting accurate determination of pure tone hearing acuity. The test system consists of an audio signal source which may be the continuous or pulsed sine wave output of an audiometer, audio frequency signal generator, audio oscillator, or tape recorder wherein said stimulus signal is applied to a phase modulator. The phase modulator may be either an electronic or mechanical device or any combination thereof for periodically shifting the phase of the stimulus signal a predetermined amount. The phase modulated signal may be applied directly to an acoustic transducer or transducers if of sufficient amplitude or it may be amplified by an audio amplifier or amplifiers prior to such application. The subject may also be biological organisms, an animal or a material wherein the invention disclosed accomplishes a test function other than that confined to hearing.

Digital signal generator

Abstract: There is provided a digital signal generator for producing accurate digital signals according to the detected state of a combination consisting of mechanical and electrical elements. The generator has a signal section consisting of a predetermined conductor pattern including a digital signal pattern and a timing signal pattern and a contact group slidable over the signal section to take out digital signal and timing signal. A digital signal is selectively provided in correspondence to the relative position of the signal section relative to the contact group, and the accuracy of the digital signal is ensured by so arranging that it is provided with the timing signal prevails at a timing signal contact in the aforesaid contact group.

Four-channel stereophonic reproducing system for reproducing discrete four-channel stereophonic discs

Abstract: In a four-channel stereophonic reproducing system of the type in which a first, second, third and fourth audio signals are reproduced from two stereophonic composite signals which are respectively comprised of a left side signal consisting of a main channel signal composed of the sum of the first and second audio signals and a sub-channel signal obtained by frequency modulating or phase modulating the difference between the first and second audio signals, and a right side signal consisting of a main channel signal composed of the sum of the third and fourth audio signals and a sub-channel signal obtained by frequency modulating or phase modulating the difference between the third and fourth audio signals, a detector circuit for detecting each sub-channel signal is followed by a filter circuit for eliminating undesired higher frequencies whereby to eliminate higher audio frequencies including increased noise components to improve the S/N ratio, and at the same time a phase correction circuit is provided in the reproducing section for each main channel signal to correct for any phase distortion due to the filter circuit whereby to ensure a greatly improved separation.

Method and circuit for recording audio signals on magnetic tape

Abstract: A method and circuit for recording an audio signal on magnetic tape wherein a bias signal in the form of a square wave is superimposed upon the audio signal before the latter is fed to a magnetic head for recording to cause the audio signal to operate on a linear portion of the transfer characteristic curve for the tape.

Audio threshold leveler with noise level suppressor

Abstract: In a radio receiver, an audio threshold leveler and noise level suppressor, for keeping the audio output level constant for input signals above a threshold level, and providing no signal output for detected audio inputs less than receiver noise. The first stage employs in its input a diode connected to conduct at low input audio levels so that it holds the active device of the stage at a low gain point of operation, and to be back biased as the input audio signal is increased, thereby causing AC degeneration which counteracts the increasing device gain. The output from the first stage is coupled through cascaded amplifier stages to a peak detector which derives a signal representative of the input audio level, which signal is connected to and biases the first stage diode so as to achieve the desired circuit response.

Power supply switching circuit for combined audio system

Abstract: In a combined audio system including main audio apparatus, auxiliary audio apparatus comprising at least one of a phonograph record player and a magnetic recorder and/or reproducer having automatic shut-off mechanisms, a power supply switching circuit is disclosed comprising a main switch and a plurality of auxiliary switches for applying power to the main audio apparatus and the auxiliary audio apparatus. The auxiliary switches are controlled by the automatic shut-off mechanism to de-energize the auxiliary audio apparatus and, additionally, selectively supply power therethrough to the main audio apparatus whereby the main audio apparatus is de-energized when the auxiliary audio apparatus is de-energized.

Audio output stage

Abstract: An audio output amplifier powered from a television horizontal circuit has a constant current source series coupled to the audio output stage. As the audio signal varies, the constant current divides between the output stage and a loudspeaker coupled in parallel with it in accordance with the strength of the audio signal. Thus a constant load is presented to the horizontal circuit, which does not affect the deflection.

Digital Control of High-Bandwidth Signals

Abstract: The interest in on-line digital control of processes handling signals with higher and higher frequencies, has focussed attention on the errors due to sampling and digital processing delays. The proposed solutions have shown an order of magnitude increase in the accuracy of the control tasks. However, like will be shown in this paper, stability of these proposed solutions shows the need of a careful interface design. Higher order digital filtering has detrimental effect on heavily damped responses. Limits are put on the bandwidth-damping combination and most useful tables are made available for further reference in practical work.