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An apparatus for and a method of processing a multi-channel audio signal using space information. The apparatus includes: a main coding unit down mixing a multi-channel audio signal by applying space information to surround components included in the multi-channel audio signal, generating side information using the multi-channel audio signal or a stereo signal of a down-mixed result, coding the stereo signal and the side information, and transmitting the coded result as a coding signal; and a main decoding unit receiving the coding signal, decoding the stereo signal and the side information using the received coding signal, up mixing the decoded stereo signal using the decoded side information, and restoring the multi-channel audio signal.

A method of processing and reproducing an input audio stereo signal in an audio signal processing system comprises the steps of (1) splitting a side signal into a first and a second intermediate signal, where the first intermediate signal is equal to the side signal and the second intermediate signal is equal to the first intermediate signal phase shifted 180°, (2) attenuating the mid signal by a factor a which compensates for imperfections in the balance between the mid and side signals appearing in the audio reproduction stage, (3) adding the attenuated mid signal to both of the first and second intermediate signals, so as to form the output audio stereo signal, and (4) directing the output stereo signal to an audio stereo signal reproduction system, comprising a pair of loudspeaker units located in close proximity to each other. A suitable audio stereo signal reproduction system comprises a pair of loudspeaker units (2', 2'') having a common baffle and each pair of loudspeaker units (2', 2'') is positionable as a unitary assembly in close proximity to each other.

Vibrator comprising a single vibration generator coupled with the medium by a coupling element and means for controlling the generator, suited to apply thereto, on each emission, a single pilot signal obtained by combination of at least two signals of different frequencies (f 1 , f 2 ), fixed or preferably variable within at least partly separate frequency bands, and non-linear elastic transmission means suited to generate in the medium vibrations at a frequency depending on the frequency difference of the two vibrational signals. The exploration method comprises using the vibrator in order to emit very low-frequency vibrations in the medium reception by pickups (R) of the waves reflected by the medium in response to the vibrations emitted and recording thereof, and selection by correlation of the vibrational signals with a synthetic signal whose frequency is connected with the frequency difference of the signals forming the pilot signal.

A system for controlling distribution of sound in a multi-channel sound system such as a "surround sound" system in a movie theater. Control signals are used to steer, or distribute, portions of the sound signal between designated speakers. In a preferred embodiment the control signals are provided with the sound signals, themselves, and are separated from the sound signals by using a pilot signal or signals.

An intercomparison is presented of multi‐tone, low‐level signal detectability in a shallow water environment using various array configurations and processing approaches. The data were collected west of Point Loma in 200‐m‐deep water during SWellEx‐96 which was carried out in May 1996. The multi‐tone transmissions covered the 50‐400 Hz band and consisted of 13 sets of tonals each having a pilot tone and 4 lower‐level tonals. These were broadcast from a source towed at 60‐m depth. Two 120‐m aperture, 64‐element arrays were deployed from the R/P FLIP—a vertical array and a tilted vertical array (tilted westerly at 45 deg). In addition, a 240‐m aperture, 32‐element horizontal array (slightly bowed) was deployed on the seafloor approximately 2‐km south of FLIP and oriented SW to NE. Broadband adaptive spatial processing has been carried out on the data; matched‐field processing in the case of the two vertical arrays and both matched‐field processing and plane‐wave beamforming in the case of the horizontal array. The low‐level signal detectability results for the various array configurations and processing approaches will be intercompared. [Work supported by ONR, Code 321(US).]

An improved theater surround sound system incorporates a screen top speaker and an overhead speaker driven by corresponding upper surround channels to more accurately reproduce sounds produced from above the listener. These top surround channels are encoded along with the left and right surround channels. A pilot signal is used to direct the sound from the side surround channels to the upper surround channels when needed.

A method and apparatus for transmitting a digitally modulated Quadrature Phase Keyed (QPSK) audio carrier signal, or a digitally modulated Quadrature Partial Response System (QPRS) audio carrier signal, wherein the audio carrier signal is located 1.2 MHz below the video carrier of an NTSC signal. This places the digital audio signal 300 KHz above the analog FM sound center frequency of the NTSC signal in the adjacent lower channel, 4.8 MHz above the video carrier of the adjacent lower channel NTSC signal and at the edge of the lower vestigal video sideband components of the NTSC signal with which the digital audio signal is associated.

A system for calibrating a sound field enabling the maintenance of a natural presence when stereophonic broadcasting is interrupted comprises means (1021R,1021L; 32) for adjusting the amplitude of an R-channel signal and an L-channel signal output from a stereophonic tuner, and for changing the output phases in accordance with a control signal; means (1022; 32) for mixing an R-channel signal and an L-channel signal output from said amplitude adjusting means; means (1023; 32) for generating a calibrating signal in accordance with an output signal from said mixing means (1022; 32); and means (2024; 32) for controlling the gains and output polarities of the signals from the amplitude adjusting means in accordance with the state of a pilot signal output from said stereophonic tuner that designates whether or not the sterephonic broadcasting is continued. When a stereophonic broadcasting signal is interrupted as electric field has weakened, a pilot signal which designates that electric field is strong enough to separate an R-channel signal and an L-channel signal from a signal received by the tuner, is also interrupted. This interruption of the pilot signal changes gains and/or phases which act on an R-channel signal and/or an L-channel signal which are applied to a sound field calibrating system.

A stereo decoder for use in a stereo FM radio receiver includes a phase-locked loop; for detecting the 19 KHz pilot signal in the FM composite signal; for generating the 38 KHz subcarrier for use as a reference signal to a double balanced gating circuit that combines he L-R and L+R components of the stereo composite signal to produce the left audio and right audio signals separately; and for providing a 19 KHz reference signal for use in the pilot detector and pilot indicator circuit. The phase-locked loop includes a mixer to which a 19 KHz reference and the composite signals are applied, a low pass filter switchable from a first bandpass of about 300 Hz to a second bandpass of about 10 Hz connected to the output of the mixer a voltage controlled oscillator connected to the output of the filter that has a natural operating frequency of 38 KHz and a divide-by-two circuit connecting the oscillator to an input of the mixer. The bandpass filter is normally (in the pilot search mode condition) switched to the 300 Hz bandpass and when the pilot indicator circuit is actuated the bandpass filter is switched to the 10 Hz bandpass (pilot locked mode).

The invention provides an apparatus for seismic prospecting which is to effect a correlation in real time between a pilot signal and a picked-up seismic signal. With N being the number of samples corresponding to the desired thoroughness of investigation, the apparatus comprises the following: a buffer of N samples of the pilot signal; at least one buffer for a sample of the picked-up signal; at least one calculation circuit, in which the correlation operations are carried out; at least one result memory, which is to contain the N points of the correlation function; and a circuit for addressing the memories.

A triphonic sound system in which three independent stereophonically related audio frequency source signals L, R and C are combined to derive three other audio frequency signals M, S, and T which respectively comprise (L+1.4C+R, (L-R) and (-1.4C). In a preferred transmitter embodiment, useful in television broadcasting, the audio signals S and T modulate two quadrature-related sub-carriers of the same frequency to develop two double-sideband, suppressed-carrier signals, the frequency of the subcarriers being sufficiently high as to assure a frequency gap between the lower sidebands of the modulated subcarrier signals and the audio frequency signal (L+1.4C+R). The aforementioned signals, and a pilot signal having a frequency which lies within the frequency gap, are combined and frequency-modulated onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers. The receiver is operative in response to reception of the high frequency carrier to reproduce each of the audio frequency source signals L, R and C, and includes means for reproducing conventional monophonic and two-channel stereophonic broadcasts. The described matrix equations are amenable to and useful with multi-channel television sound systems currently under consideration for future broadcast service in the United States.

A compatable stereophonic television sound transmission system for transmitting left and right audio signals in conjunction with a television broadcast wherein video information is conveyed on an amplitude-modulated carrier in a frequency channel having defined frequency limits. The system includes at a transmitter location a multiplex generator for generating a composite signal having a first component representative of the sum of the audio signals, a second component comprising an amplitude-modulated suppressed carrier subcarrier signal representative of the difference between the audio signals, and a pilot component representative of the phase and frequency of the suppressed carrier. The composite signal is utilized to frequency-modulate a sound carrier to develop an RF signal component which is added to the television channel at a discrete frequency spacing from the video carrier. The system includes at a receiver location a tuner for converting the transmission channel to an intermediate frequency, a filter for separating the sound signal therefrom, and a detector for deriving the composite signal from the sound signal. The composite signal is demodulated in a stereo demodulating stage to develop the left and right audio signals. Improved noise performance is obtained in the system by applying preemphasis to the left and right audio signals, preemphasis of the composite signal, enhancement of the second composite signal component, and/or Dolby-B processing of the left and right audio signals or to the composite signal. An adapter is shown for utilizing the system for bilingual programming.

A system for transmitting wide-band signals over a narrow band by directly transmitting low frequency range signals and transmitting amplitude information of partial upper frequency ranges on pilot frequencies is made compatible with existing receivers by making the pilot frequency signals imperceptible in ordinary receivers through the use of a phenomenon known as the masking effect. This is achieved by positive modulation of the pilot frequencies and attentuation to a level 10 db below the level of the low frequency range. If sequential transmission is used, a low level sync signal is produced that does not exceed the signal-to-noise level in existing receivers and is therefore suppressed. In the receivers of the present invention, the low level sync signal is selectively evaluated for control and synchronization of a clock generator but is suppressed below the signal-to-noise ratio of the output and is therefore made inaudible. The sync signal is further processed to control the gain of a modulated pilot signal amplifier and to automatically switch off the upper frequency range signals in the event of sync signal failure or synchronization failure.

In an apparatus for recording and/or reproducing a television signal with multiplex audio signals, a pilot signal is recorded on one or both of the audio tracks of a video tape in a manner to identify the mode of the multiplex audio signals and each pilot signal is detected to establish such mode when reproducing. For example, the frequency of the pilot signal may be changed for identifying different modes of the multiplex audio signals, such as, the bilingual mode and the stereo-phonic mode, with the pilot signal of selected frequency being recorded on one of the audio tracks, or the pilot signal having a certain frequency is recorded on one of the audio tracks in the case of the bilingual mode, and on the other audio track of the tape in the case of the stereo-phonic mode. In still another embodiment, the pilot signal is recorded in both audio tracks of the tape and the phase relation of the recorded pilot signals is varied to identify the mode of the multiplex audio signals.

Apparatus for receiving an AM stereophonic signal of the type having monaural information represented by amplitude modulations of a signal carrier and stereophonic information represented by phase modulations of the signal carrier. A reference signal generator generates a reference signal that is synchronized with the signal carrier of the received AM stereophonic signal. In one embodiment, the reference signal generator is a phase-locked loop which generates a reference carrier whose frequency is substantially equal to the signal carrier frequency and whose phase is locked to a predetermined signal carrier phase. An amplitude limiter limits the AM stereophonic signal to remove amplitude modulations of the signal carrier and thereby produce an amplitude-limited signal carrier. A demodulator demodulates the information represented by the AM stereophonic signal, and a detector is provided to detect if the stereophonic information will be properly demodulated. A switching arrangement is controlled by the detector to supply the reference signal to the demodulator, whereby the stereophonic information is demodulated, or to supply the amplitude-limited signal carrier to the demodulator, whereby the monaural information is demodulated.

An electrical system is described which permits the use of sound film, with its limited signal‐to‐noise ratio, as a recording medium for wide‐range stereophonic reproduction of symphonic music. Noise reduction is accomplished both by pre‐equalization, rising to 18 db above 8000 cycles, and by automatic signal compression and expansion of 30 db. To secure maximum suppression of noise and freedom from distortion, a pilot‐operated, fiat‐top compandor system was selected. In each channel low level signals are recorded on a separate track with constant gain 30 db above normal, which places them above the film noise. Higher‐level signals cause automatic gain reductions and are recorded at substantially full modulation. These signals vary the intensity of a pilot tone, which in turn controls the compressor gain. There is a pilot frequency for each of the three channels, and the three are combined and recorded together on the fourth film track. During reproduction they are separated by filters, and operate expand...

This paper describes two methods for making an objective quantification of the location of the sound image that results from binaural acoustic stimulation. The first method (“nullity method”) is based on reversing, by means of a changeover device equivalent to a double‐pole, double‐throw switch, the binaural signals—switching the signal from the right ear to the left ear and the signal from the left ear to the right ear. Adjustments are made in one of the two channels until this reversal does not appear to change the location of the sound‐image. The second method (“comparison‐sensation method”) involves a pilot signal, which is applied binaurally and used to produce a reference image with which the experimental sound image is compared. These methods are more objective than the ones usually employed because they require the observer to function only as a null indicator. Data are presented which show that the “nullity method” yields data that are much less variable than those obtained with the ordinary method.