Showing papers on "Audio signal processing published in 1987"

Method of transmitting or storing masked sub-band coded audio signals

Abstract: In the transmission of audio signals, the audio signal is digitally represented by use of quadrature mirror filtering in the form a plurality of spectral sub-band signals. The quantizing of the sample values in the sub-bands, e.g. 24 sub-bands, is controlled to the extent that the quantizing noise levels of the individual sub-band signals are at approximately the same level difference from the masking threshold of the human auditory system resulting from the individual sub-band signals. The differences of the quantizing noise levels of the sub-band signals with respect to the resulting masking threshold are set by the difference between the total information flow required for coding and the total information flow available for coding. The available total information flow is set and may then fluctuate as a function of the signal.

Method of providing identification, other digital data and multiple audio tracks in video systems

Abstract: A method and apparatus for imbedding digital data and multiple audio (analog) track information in a video signal in a manner compatible with ordinary broadcast TV and transparent to a conventional television receiver is disclosed. The method and apparatus may provide multiple independent audio tracks and a substantial level of interaction with a viewer utilizing special reception equipment, which equipment may be utilized to provide a fully interactive system from signal sources not required to be compatible with convention receivers. The method and apparatus includes the ability of imbedding both analog and digital signals in a video signal, and while advantageous for interactive TV systems, may be used for a multitude of purposes in various video systems.

Noise reduction processing arrangement for microphone arrays

Abstract: A sound processing arrangement couples sound from a prescribed environment through a fixed microphone array to a signal processing arrangement having a specifiable preferred sound source location. The microphone pickup signals are combined with a set of weighting signals to adjust the directional response pattern in successive analysis time intervals. The weighting signals are modified in each analysis time interval so that the total acoustic signal power of the signal processing arrangement output signal is decreased toward a minimum while substantially unity power transfer of sound signals from said preferred location is maintained at all frequencies over a prescribed frequency range. In this way, the preferred source location is in the main beam while unwanted sound source locations are at the null points of the adjusted directional response pattern.

Signal transmission system for a CATV system

Abstract: A CATV (cable television) signal transmitting system for use with a broadcast satellite system includes a receiving stage for receiving a broadcast satellite station signal consisting of base-band video signals and a sub-channel digital audio signals PSK (phase shift keying)-modulated on sub-carriers, demodulators for deriving the video signals and digital audio signals, first modulators for modulating the main carriers of a plurality of CATV channels by the video signals, a second modulator for modulating the main carrier of a different channel by the digital audio signals in time-division manner. The mixed output signal from the first and second modulators is transmitted through a CATV transmission line. A CATV signal receiving system is also provided to produce video signals and digital audio signals which are converted into a plurality of channels of analog audio signals.

Active attenuation system with increased dynamic range

Abstract: An active acoustic attenuation system is provided that increases dynamic range by adjusting the amplitude of the input signal and the error signal at respective model and error inputs and providing automatic self-calibration. Input and error transducers provide analog input and error signals which are converted by an analog to digital converter to digital input and error signals for input to the model . Digital to analog converters have digital inputs from respective digital input and error signals and operate in an analog to analog mode with analog inputs from respective input and error transducers and analog outputs to the analog to digital converter . Dynamic range is also increased by adjusting the amplitude of the correction signal to the output transducer

Data compression system and method for audio signals

Abstract: Audio signals such as ECG, speech and music are digitally processed to reduce the bit-rate needed for accurate transmission, known as minimizing the entropy of the signal. The transmitter features a digital compression filter with zeros restricted to certain points on the unit circle, and Huffman encoding for transmission. The receiver features a digital decompression filter with poles at the zero locations, but shifted inside the unit circle to prevent error-ramp build-up.

Audio digital/analog encoding and decoding

Abstract: Apparatus and an associated method are described for encoding an analog signal to a digital representation thereof and then decoding the same to reconstruct the original analog signal with reduced quantization noise and error. The analog signal is first adaptively pre-emphasized. A series of samples of the pre-emphasized signal are then obtained and encoded to create a series of digital representations which have a lower order resolution than the samples. The difference between each sample and its corresponding lower resolution digital representation is obtained and combined with the next sample. Decoding of the combined signals takes place in a complementary manner to create an approximate analog output signal, which is then de-emphasized in a manner complementary to the pre-emphasis to produce an analog output signal closely approximating the original analog signal. In a fully digital implementation the samples are converted to a digital format with a higher order resolution; the digital representations are obtained from the digitized samples, and the difference measurements are combined with the samples in their digital format. In a hybrid digital/analog implementation the difference is combined with the analog signal prior to sampling.

Method of and apparatus for recording and/or reproducing a picture signal and an associated audio signal in/from a record carrier and record carrier obtained by means of the method

Abstract: Finite audio and video signals are subjected to a digitizing code format and converted into blocks of audio and video words respectively. For the transmission of these blocks via a record carrier (2), for example a compact disc, the words are arranged in frames. Each frame has a frame header (8.1) and a data field (8.2). Such a data field contains information words in the form of either audio words or video words. The header indicates whether the associated data field contains audio words or video words. At least two audio signals associated with a video signal are recorded on the record carrier. An example of this is a "slide show" in which the explanatory text is available in two or more languages (e for English, ffor French). The frame header of the frames containing an encoded audio signal also indicate to which one of the two or more audio signals the information words in an audio frame belong. Further, reference signals and additional frames (6) are recorded in the record carrier. For each of the two or more audio signals associated with a picture (or video) signal the additional frames contain time information on the time interval between the instant of detection of a reference signal after reading and the instant at which a picture signal read is to be displayed on a monitor (50). An apparatus for recording or reproducing the above signals is described.

Driver circuit for driving a light emitting element by superimposing an analog sub-information signal over a digital main signal

Abstract: A driver circuit for driving a light emitting element with a signal generated by superimposing an analog sub-information signal over the pulse string of a digital main signal. The driver circuit includes an input interception detector for detecting any interception of the digital main signal, and a gain-controlled amplifier for increasing the gain of the analog sub-information signal when the digital signal is intercepted.

Fiber optic data transmitting system

Abstract: A fiber optic digital data transmitting system is disclosed which has the capability of transmitting and accurately reproducing digital data signals at the receiver even when the optical signal is attenuated in the fiber optic transmitting medium. A composite signal is produced at the transmitter which is the time coincident sum of the non-zero amplitude of the digital data signal to be transmitted and a time varying signal which encodes each non-zero amplitude of the digital signal and other information. The composite signal modulates an optical carrier signal which is coupled to a fiber optic transmission medium which couples the transmitter to the receiver. At the receiver, the presence of each time varying signal is detected as a non-zero amplitude of the digital signal. Circuitry is are provided in the receiver for producing a pulse in response to the detection of each time varying signal for reproducing the transmitted digital signal and for detecting any information in addition to the non-zero amplitude of the digital signal which has been encoded in the time varying signal. The present invention is compatible with existing PCM systems which utilize threshold detection.

Apparatus for recording and reproducing digital signals

Abstract: A digital signal recording and reproducing apparatus comprising a dynamic range compression/expansion apparatus. The compression/expansion apparatus (16) receives a digital signal from, for example, an analog-to-digital converter (II) and compresses the dynamic range of the digital signal and the so compressed digital signal is supplied to a recording signal processing circuit (27) in the recording operation mode, while the apparatus receives a digital signal reproduction output from a recording/reproducing head (29, 30) and expands the dynamic range of the reproduced digital signal and the so expanded digital signal is supplied to, for example, a digital-to-analog converter (12) in the reproducing operation mode. The compression/expansion apparatus includes a circuit for controlling the transient response of the apparatus, that is, for controlling the operation of the compression/expansion of the dynamic range of the digital signal during transient of the digital signal so that recording of the digital signal is performed at a high density with a high quality, without suffering breathing effect, overflow, etc.

Method and system for synchronization of an auxiliary sound source to motion picture film, video tape, or other picture source containing a sound track

Abstract: A method and system for synchronizing a digital signal of an audio message at higher quality with another signal of the same audio message at lower quality. The invention synchronizes an auxiliary high quality audio digital sound signal source with the ordinary quality analog sound signal coming from a conventional analog sound track on motion picture film as the motion picture is being shown and maintains effective synchronization in spite of missing segments of the sound track due to film splices. The invention does not require synchronization tracks, markers, codes, time codes or other extrinsic data. The only requirement is that the higher qualtiy audio message recording, e.g. in a digital medium, be made from the same "master recording" (or a high quality duplicate thereof) as the sound track so that the auxiliary recording have the same informational content as the sound track. In order to maintain synchronization of the high quality audio message in spite of missing segments of the lower quality audio message, the higher quality message is caused to precede the lower quality message, and is temporarily stored in time-delay means, such as a FIFO overwriting memory store. Correlation is achieved by re-iterative subtractions between digital numbers representative of characteristics of the absolute value envelope of the ordinary quality message signal and digital numbers representative of characteristics of the absolute value envelope of the high quality message. When the missing segments of the cinema sound track amount to more than the time-delay storage capability of the time-delay means, the system immediately smoothly "fades" over to utilize the conventional analog sound track of the cinema film for uninterrupted sound accompanying the motion picture being viewed by the theater audience. Re-synchronism is quickly achieved, and the system immediately automatically smoothly "fades" back to the higher quality sound.

Universal telecommunications audio coupling device

Abstract: Input coupling apparatus for coupling a telecommunications link, such as a telephone line, to an audio device, such as a recording channel of a telecommunications logger. Input terminals connect the coupling apparatus to the telecommunications link, such as to the tip and ring leads of a telephone line, for receiving audio signals. Voltage, current and remote sensing devices are coupled to the input terminals for detecting an active mode, such as an off-hook condition, during which audio signals are present. When connected to a telephone line, either an off-hook voltage condition or an off-hook current flow is sensed to produce an off-hook signal. When coupled to another communications link, such as a radio link, an external, simulated off-hook signal is detected. A selector is coupled to the voltage, current and remote sensing devices and selects one of those devices to supply the off-hook signal to the audio device, for example, to enable a logger to record audio signals. An audio amplifier is coupled to the input terminals for applying received audio signals to the audio device (e.g. to apply those signals to the recording channel of a logger).

Synchronising systems for digital apparatus

Abstract: A synchronizing system for use with a plurality of digital signal reproducers includes a plurality of digital signal reproducers, each having a digital I/O modulator, a digital I/O demodulator and a decoder; a digital signal multiplexer supplied with the output signal from the plurality of digital signal reproducers, and for producing a frame synchronizing signal, a plural channel of digital signals; the digital signal multiplexer including a clock pulse generator, a word synchronizing signal generator, a digital I/O modulator and a digital I/O demodulator. The corresponding digital I/O modulator and digital I/O demodulator are coupled to each other so as to synchronize the plurality of digital signal reproducers.

Radio with digitally controlled audio processor

Abstract: A mobile radio is disclosed which includes an integrated circuit audio processor which operates under the control of at least one microprocessor. The audio processor provides basic transmit/receive audio filters, tone signaling filters, squelch filters, an RF power level control circuit, a DC voltage measuring circuit, a volume level adjusting circuit, and a transmit level adjusting circuit. In the audio processor, audio bandwidth, tone filter response, squelch filter response and other operating characteristics are adjusted by an incoming data bit stream from the controlling microprocessor. In addition, in response to data received from a microprocessor, the audio processor is controlled, for example, to have its receive audio path closed and its transmit audio path opened to switch from the receive to transmit mode. Based on digital control data received at predetermined input pins, the audio processor of the present invention has its filter responses, signal paths, and other characteristics altered in a predetermined manner to configure the audio processor to appropriately operate in the transmit and receive modes.

Television interrupt circuit

Abstract: An interrupt circuit monitors a television audio demodulator or an external video input circuit and interrupts the video signal to CRT and the audio signal to television speaker(s) whenever a lost signal condition is detected. In the preferred embodiment, a lost signal condition is detected by monitoring the voltage level of the signal from the audio demodulator or the external video input circuit and generating a detect signal whenever the voltage exceeds a predetermined threshold. When a television signal is lost, both the audio demodulator signal and the external video signal constitute a noise signal that has a voltage amplitude that is greater than the normal operating range of either of these two signals. In the preferred embodiment, when a detect signal is produced, both the video signal to the CRT and the audio signal to the television speaker(s) are interrupted and alternate video and audio signals are provided to the CRT and speaker(s) by a microprocessor. These alternate signals will announce the lost signal condition to the viewer.

Digital signal processing method for real-time processing of narrow band signals

Abstract: A digital signal processing method for real-time processing of narrow band signals to provide for reconstitution of dynamic amplitude and harmonics beyond the passband. The method utilizes a digital microprocessor implementing a digital algorithm upon a digitized sample of the analog signals. After processing digital-to-analog conversion circuitry may be used to reconvert the processed digital signal into a processed analog output signal for further use. The digital processing effectively provides a primary voltage compressor (PVC) function for processing signals in m different frequency sub-bands by gain factors, and a summing function for digitally summing the gain products so realized, to provide a primarily compressed signal. The processing method then further effectively provides a secondary dynamic voltage compressor (SDC) function for processing the PVC signal in within n different frequency sub-bands by digitally multiplying signals with each of such sub-bands by gain factors. The further gain products so realized are digitally summed to provide a processed digital output. An AGC gain calculation is also provided by the digital processor for providing a gain-corrected digital output which may then be supplied to D/A converter circuitry. Both fast and slow gain averaging are utilized in making the gain calculation for gain multiplication within each of m sub-bands of the PVC function. The sub-bands m and n of the PVC and SDC functions may be equal in number and have corresponding frequency domains.

Recording audio signals

Abstract: In a method of recording digital audio signals of four audio channels in association with a digital video signal in oblique tracks using a 4-head digital video tape recorder, the digital audio signals are assembled into error-correction blocks each comprising two audio data words and two error-correction code check words, each oblique track comprises in sequence first and second sectors at the beginning of the track, a central portion in which the video signals are recorded, and third and fourth sectors at the end of the track, the audio data words and the check words are distributed to the four heads to be recorded in the sectors, and the assembly, the error-correction code and the distribution are such that the four audio channels can be correctly reproduced even if, on reproduction, any two of the sectors are lost from each reproduced track, or any two of the four heads fail to supply a reproduced output.

Method and apparatus for recording video and audio signals in successive tracks on a record medium

Abstract: A method and apparatus for recording and reproducing an information signal comprised of a video signal and an audio signal in a plurality of successive parallel tracks on a magnetic tape, each track including a first audio section followed by a video section, by converting the audio signal into a PCM digital audio signal; compressing the PCM audio signal; frequency modulating the compressed PCM audio signal to produce an output PCM audio signal; and recording the output PCM audio signal and the video signal in the plurality of successive tracks such that one field interval of the video signal is recorded in the video section of each track and the output PCM audio signal corresponding to one field interval of the video signal is recorded in the audio section of each track and corresponds to the video signal in the leading portion of the previous successive track and the video signal in the trailing portion of the previous alternate track, wherein the audio signal recorded in each track is delayed by a maximum of 1.5 field intervals from the video signal to which it corresponds.

Wide dynamic range digital to analog conversion method and systems

Abstract: A method and apparatus well suited for the conversion of a digitized audio signal into analog form with as wide a dynamic range as possible. A digital dither signal is added to a digital audio or like data signal to provide a digital data/dither signal. This digital data/dither signal and the digital dither signal are both converted into an analog data/dither signal and an analog dither signal respectively, and the analog dither signal is subtracted from the analog data/dither signal to obtain an analog data signal equivalent to the digital data signal. The level of the incoming digital data signal may be so high that when the digital dither signal is added thereto, the total level of the data/dither signal may exceed the capacity of the digital to analog converter in use. In that case the digital dither signal is either gated off or reduced in level, with the result that the digital to analog converter inputs either the data signal only or the data/dither signal having a total level not exceeding its capacity.

Waveform sequence trigger system

Abstract: A digital signal processing apparatus has: an A/D converter for A/D converting an input signal to be processed to a digital signal, an analog comparator for comparing the input signal with a predetermined threshold voltage and generating a comparison signal as a binary signal, a first input device for inputting at least binary data of a reference wave to be triggered, a discriminator for discriminating a coincidence between the binary signal from the analog comparator and the binary data entered at the first input device and generating a coincidence signal, a fetching section, triggered in response to the coincidence signal from the discriminator, for fetching the digital signal from the A/D converter, and a processor for performing predetermined processing of the digital signal fetched by the fetching device.

Real-time video signal processing device capable of typically executing interframe coding

Abstract: In a real-time video signal processor for processing an input digital video signal divisible into a succession of principal blocks each of which has at least one scanning line and a time duration shorter than a frame period, each principal block is divided into at least two partial blocks with each scanning line divided into the respective partial blocks. A plurality of signal processing modules are assigned with the respective partial blocks of each principal block, respectively. Responsive to the input digital video signal and an additional digital video signal, the signal processing modules process the respective partial blocks of each principal block into processed signals during the time duration, respectively. Each processed signal comprises a first partial signal used as an output signal of the processor and a second partial signal. A delaying circuit delays the second partial signals derived from the signal processing modules into a delayed signal having a delay equal to a difference between the frame period and the time duration. The delayed signal is used as the additional signal. A plurality of the real-time video signal processors may be connected in cascade to each other. Two memory units may be used instead of the delaying circuit. Readout operation of each principal block from the memory units is controlled by control signals produced by a control signal producing circuit. Principal blocks read out of the memory units are supplied to the signal processing modules.

Digital signal processing in the UK

Abstract: Digital signal processing subsystems are increasingly-reliant on standard parts in volume production — an area in which UK manufacturing is not strong. However, UK strengths are now being better exploited

Low-pitched sound creator

Abstract: An analog sound signal is outputted Low-frequency components are selected from the outputted analog sound signal so that a low-pitched sound signal is derived from the analog sound signal A key of the low-pitched sound signal is lowered so that a very-low-pitched sound signal is derived from the low-pitched sound signal The analog sound signal and the very-low-pitched sound signal may be converted into corresponding sounds respectively

Optical communication apparatus and method for telephone supervisory and audio signals

Abstract: The invention is for an optical communication apparatus for bidirectionally transmitting and receiving supervisory and audio signals. The apparatus includes a telephone line interface unit that receives electric audio and supervisory signals and converts them to optical signals. It is also includes means for receiving optical signals representing audio and supervisory signals. A data unit receives the optical audio and supervisory signals from the interface unit and converts them to electric audio and supervisory signals, and also includes means for receiving electric audio signals and supervisory signals and converting them to corresponding optical signals. An optical link connects the telephone line interface unit and data unit for bidirectional optical communication. A method of practicing the invention is also included.