Abstract: A digital surround sound decoder. The decoder uses an architecture including two signal processing chips to achieve a program that can decode audio data at sufficiently high resolution. The decoder performs in real time and is compatible with standard surround sound formats. The decoder includes software that utilizes table lookups for critical functions in the decoding process. The processing flow of the decoder's program takes advantage of the multi-function capability within the specific processors used in the design while using a minimum number of program instructions. The program implements band pass filtering, sum-difference calculations, fast-attack slow-decay integration, summation and reciprocal processing, determination of fast and slow modes, look-up table indexing, adaptive matrix processing and various other functions to generate decoded surround sound signals from encoded left and right signal inputs.

Abstract: An expandable multi-dimensional sound system has two modes of operation. Prior to the detection of a 20 kHz tone, the system is configured such that input audio panned hard to the left or right will result in the center and surround channels steering down so that the signal is only passed through the left front and right front channels, respectively. Mono information is fed only through the center channel, as the left and right front channels cancel any center channel or mono information. Material panned hard to the surround position steers down the front left and right channels and is only fed to the rear surround channels. No information is fed to the front center channel due to the fact that the signal contains only difference information. Directional steering to the rear channels is still provided in the absence of any hard broadband left or right panning. Upon the detection of a 20 kHz tone, the system is re-configured such that the left and right front channels and the center channel become disabled.

Abstract: An adaptive high-fidelity perceptual subband encoder for spatially directional multichannel audio signals, using a mixture of individual-channel subband coding with subband-steered composite-channel signal coding that combines the spectral components of the individual channel subbands selected for steering. The composite channel representation includes a subband steering control signal which either conveys the levels of the spectral components from all the steered channels, or represents the apparent directions (net directional vectors) of the spectral components from all the steered channels.

Abstract: A surround sound processor for redistribution of stereophonic audio signals into multiple channels for presentation on a plurality of loudspeakers surrounding a listener has an improved direction detector filter circuit, a peak hold circuit in the direction detector for better dynamic separation, improved time constants in the servologic circuit, improved linearity correction in the control voltage generator to match the characteristics of the new voltage controlled amplifiers which are applied to the separation matrix, a separation matrix having cancellation of unwanted signals wihtout gain modification for desired signal components, and improved shelf filters in the rear channel outputs.

Abstract: The present invention relates to an audio signal processing apparatus and method, and more particularly to an apparatus and method for processing an audio signal according to surround modes in which a surround-sound of an original sound, in accordance with surround modes, can be reproduced by carrying surround code information with the audio signal being transmitted and by detecting the surround code information upon receipt of the audio signal.

Abstract: A transmission channel may be utilized for a combination of wide-band signals and auxiliary signals, while still providing improved reproduction accuracy. Digital sub-signals or subband signals representing at least first and second data-reduced components are combined with at least one auxiliary digital signal in defined frame portions before transmission. The auxiliary signal may be user-discernible information such as third and fourth audio channels, so that a four channel surround sound signal is transmitted; or teletext or video or picture information may be provided. Sampling reduction and filtering into subbands may be applied to the auxiliary signal as well as to the first and second signal components.

Abstract: An audio signal processing arrangement includes a first filter (20) for splitting off signal components from the left channel signal (L) at least within one frequency band. Signal components are split off from the right channel signal (R) by a second filter (23). The output signals of the filters (20 and 23) are compared with the right channel signal (R) and the left channel signal (L), respectively. The filter parameters of the filters (20 and 23) are adjusted to values at which there is maximum correlation between the compared signals according to a given criterion. The center channel signal is derived in dependence on the filter adjustment. This can be effected by combining the output signals of the filters (20 and 23).

Abstract: The invention relates generally to transmitting and receiving multiple channels of information, particularly audio information which represents a multidimensional sound field. More particularly, the invention relates to devices and methods which provide signals that are compatible with multi-channel receivers and with matrix decoders such as the decode MP-Matrix used for many motion picture soundtracks. In a multi-channel transmitter, a network prepares intermediate signals which are encoded by signal analysis processors into a signal for subsequent transmission or storage. In a multi-channel receiver, information extracted from the received encoded signal is combined in a network and processed by signal synthesis processors to provide output signals which are compatible with a matrix decoder.

Abstract: A surround sound processor for presentation of a stereophonic source program on a multiple loudspeaker array surrounding the listening area. The processor includes input signal conditioning and matrixing circuits, a control voltage generator responsive to the directional information contained in the stereophonic source signals, and a variable matrixing circuit for generating appropriate loudspeaker feed signals to create the illusion of the sound field wrapping around the listening area. The control voltage generator includes a servologic circuit employing variable time constant smoothing circuits each responsive to the difference signal between its input and its output and to a pulse signal from a one-shot triggered by threshold detectors which compare the difference signals with fixed threshold voltages. In one aspect, suitable for incorporation into an integrated circuit, a multiplier circuit and a controlled bidirectional current source charging and discharging a capacitor provides the smoothing function.

Abstract: The system includes a direction detection circuit (32) for deriving a measure (Vwh) for a direction of a direction vector (Wh) which vector, in a state area in which combinations (R,L) of signal values of the left and right channel signals are shown at specific instants, is indicative of the direction of the most powerful sound source. A circuit (33) derives from this measure (Vwh) two weight factors (w1,w2). A center channel signal (C) is derived which is a weighted sum of the left (L) and right (R) channel signal determined by the weight factors (w1,w2). In this manner a center channel signal is obtained which has a less dull sound on reproduction.

Abstract: A signal processor for sound image enhancement of stereophonic signals provides fluctuating coherence between the left channel and right channel outputs by crossfeeding a high pass portion of the left channel to the right output and a like portion of the right channel to the left output. Preferably, the crossfeed path includes a high pass filter to eliminate crossfeeding of lower frequency range components which are often reproduced monaurally in prerecorded materials. The filtering is compensated for by a shelving filter introduced in the respective channel input to boost the power of the lower frequency components to be added with the crossfed signal to produce the channel output. In the preferred embodiment, an automatic gain control varies the gain of the crossfeed in accordance with the stereo content in the input channels. In addition, the gain control includes a control for user variation of the amount of coherence to be generated at the output.

Abstract: An audio sound system decodes from non-encoded two-channel stereo into at least four channel sound. The rear channel information is derived by taking a difference of left minus right and dividing that difference into a plurality of bands. In a simplistic implementation, at least one band is dynamically steered while the other band is unaltered so as to avoid any perceived pumping effects while providing transient information to left/right, as well as directional enhancement. In a preferred embodiment, multiple bands are dynamically steered left or right, so as to enhance directional information to the rear of the listener. In both schemes, the low pass filtered output of the sum of the left and right inputs is also combined with the directionally enhanced information, so as to provide a composite left rear and right rear output.

Abstract: An audio sound system decodes from non-encoded two-channel stereo into at least four channel sound. The rear channel information is derived by taking a difference of left minus right and dividing that difference into a plurality of bands. In a simplistic implementation, at least one band is dynamically steered while the other band is unaltered so as to avoid any perceived pumping effects while providing transient information to left/right, as well as directional enhancement. In a preferred embodiment, multiple bands are dynamically steered left or right, so as to enhance directional information to the rear of the listener. In both schemes, the low pass filtered output of the sum of the left and right inputs is also combined with the directionally enhanced information, so as to provide a composite left rear and right rear output.

Abstract: A surround processor includes a time constant processing circuit for smoothing directional information signals from a detector with continuously variable time constants in order to generate one or more control voltage signals. The time constants produced by the circuit are continuously variable and responsive to both the rate of change and the amplitude of the directional information signals, such that as the difference between the controlled voltage signals and the directional information signals increases, the value of the time constants decreases to permit the control voltage signals to closely follow the directional information signals, and as the difference between the control voltage signals and the directional information signals decreases, the value of the time constants increases so that variations in the control voltage signals are smooth. Split-band processing of input audio signals to the processor is also accomplished without the necessity of placing filters directly in the audio path.

Abstract: A surround sound processor for presentation of a stereophonic source program on a multiple loudspeaker array surrounding the listening area, the processor comprising input signal conditioning and matrixing circuits, a control voltage generator responsive to the directional information contained in the stereophonic source signals, and a variable matrixing circuit for generating appropriate loudspeaker feed signals to create the illusion of the sound field spreading around the listening area, the control voltage generator having improvements in performance and reduced circuit complexity and cost. An inexpensive width-modulated pulse oscillator provides means for varying the time constants applied to directional information signals to produce control voltage signals for varying the matrixing coefficients. A new duration stretching circuit ensures tracking of the control voltages.

Abstract: In a system in which a low-bit rate encoder and decoder carries matrixed audio signals, an adaptive rematrix rematrixes matrixed signals from an unmodified 4:2 matrix encoder to separate and isolate quiet components from loud ones, thereby avoiding the corruption of quiet signals with the low-bit-rate coding quantization noise of loud signals. The decoder is similarly equipped with a rematrix, which tracks the encoder rematrix and restores the signals to the form required by the unmodified 2:4 matrix decoder. The encoder adaptive rematrix selects the matrix output signals or the amplitude weighted sum and difference of the matrix output signals. The choice of whether the matrix output signals or the sum and difference of the matrix output signals are selected is based on a determination of which results in fewer undesirable artifacts when the output audio signals are recovered in the decoder.

Abstract: Left right and surround components of a stereo signal are coded into a monaural and small co-channel providing volume steering for recreating a stereo effect with a substantially reduced bit rate. The signal is split into a sum and difference signal, the difference signal is randomized and the sum is added to the randomized difference to comprise the single audio channel. A functional relationship is solved for left and right volumes which is then transmitted for intervals on the co-channel. Decoding of the single transmission channel directs it to left, right, or surround channels based on decoding on the logic co-channel. The co-channel updates left and right volume levels which are interpolated through time to effect smooth volume change. Surround gain is determined from left and right channel gains to maintain unity total volume, with the sum of the squares of the three volume controls being unity.

Abstract: A method and apparatus for generating control voltage signals in a surround sound processor is disclosed which utilizes a one-shot monostable multivibrator for minimizing intermodulation distortion while following rapid directional changes, yet minimizing intermodulation distortion. The apparatus includes a circuit for smoothing the directional information signals derived from audio input signals each with a continuously variable time constant to generate a corresponding control voltage signal, such that each time constant depends inversely upon the magnitude of the difference between the directional information signal applied thereto and the corresponding control voltage signal generated thereby.

Abstract: A stereo audio system includes a plurality of drivers and a signal processor circuit. The signal processing circuit has at least a left channel input and a right channel input, and provides at least one processed signal on at least one output. The processed signal is characterized by a coefficient of proportionality representative of complex components of the signals on the left channel input and the right channel input. The coefficient of proportionality is at a maximum and minimum for the complex components on the left channel input and the right channel input being in phase opposition and phase coherence, respectively. Each of the signals on the left channel input, the right channel input, and the at least one output are received by at least one of the drivers, and each of the drivers receives at least one of the left channel input signal, the right channel input signal, and the processed signal.

Abstract: A method and an apparatus for processing audio signals with a directional emphasis by providing other channels besides the left and the right channels. An audio signal processing apparatus is divided into two blocks: a first block for processing digital signals of the left channel and the right channel supplied at each predetermined sampling period and outputting the signals of the left channel, right channel, and other channels which are amplified or decreased to a certain level; and a second block for detecting the level difference between the left channel signal and the right channel signal, and the level difference between the sum and the difference between the channel signals, and generating coefficients for adjusting the amplifying rate of the channels. The result is that the number of bits required for the signal processing can be reduced.

Abstract: A stereo/monaural detection apparatus for detecting whether two-channel input audio signals are stereo or monaural, wherein the level difference between the input audio signals is calculated, and after the signal representing the level difference is discriminated with a predetermined hysteresis maintained, a stereo/monaural detection is performed in accordance with the result of such discrimination, thereby preventing an erroneous detection that may otherwise be caused by any level difference variation during a short time as in a case where the sound field is positioned at the center in the stereo signals. And the discrimination with the hysteresis is partially inhibited in response to the signal obtained by discriminating the level sum of the input audio signals at a predetermined reference level, hence preventing instability of the operation when the audio input level is extremely feeble.

Abstract: A system for the multichannel reproduction of sound in which a plurality of loudspeakers connectable to a surround sound processor is disclosed. Circuits for adapting the processor to provide left and right side output signals are also disclosed. Left and right side dual loudspeakers are disclosed wherein each dual loudspeaker contains two independent drivers, one facing the front and the other the rear of the listening area, the front-facing drivers being connectable to the left and right side output signals and the rear-facing drivers being connectable to the corresponding left and right rear output signals of the processor.

Abstract: A multiple-channel audio reproduction apparatus has an audio demodulator for demodulating an input signal to produce audio signals for multiple channels. One or more signal-processing circuits process audio signals of one or more of these channels in a way suitable for reproduction by loudspeakers connected to other channels. Switches feed the processed audio signals to output terminals for those other channels. A switch controller turns these switches on if a loudspeaker is not connected to the channel corresponding to the original, unprocessed signal, and otherwise turns these switches off.

Abstract: Spectral imbalance when playing home video versions of motion pictures is overcome by a frequency response correction unit which compensates for the equalization employed during the production of motion picture sound tracks designed for playback over the standard X-curve. In addition, the frequency response correction unit may additionally or instead compensate for listener-perceived differences in the frequency response between the surround sound channel and main sound channels.

Abstract: A sound reproducer is disclosed for a Hi-vision 3-1 sound system composed of an audio signal decoding unit coupled with an AV amplifier, which amplifier has a surround processor and is originally arranged for reproducing surrounding sounds from two-channel stereophonic audio signals of the Dolby.RTM. surround system, wherein volume controllers for controlling right and left rear Hi-vision audio signals of monaural and a center front Hi-vision audio signal, and first through third switching circuits for selecting outputs of the audio signal decoding units, are provided in case of reproducing sounds of the Hi-vision 3-1 sound system, or outputs of the surround processor, in case of reproducing sounds of the two-channel sound surround system, for providing the acoustic balance of the audio signals when the first through third switching circuits are switched to reproduce the sounds of the Hi-vision 3-1 sound system.

Abstract: A surround processor includes a time constant processing circuit for smoothing directional information signals from a detector with continuously variable time constants in order to generate one or more control voltage signals. The time constants produced by the circuit are continuously variable and responsive to both the rate of change and the amplitude of the directional information signals, such that as the difference between the controlled voltage signals and the directional information signals increases, the value of the time constants decreases to permit the control voltage signals to closely follow the directional information signals, and as the difference between the control voltage signals and the directional information signals decreases, the value of the time constants increases so that variations in the control voltage signals are smooth. Split-band processing of input audio signals to the processor is also accomplished without the necessity of placing filters directly in the audio path.

Abstract: An audio signal energy level detector for use with audio signal processing is described. The energy level detector includes a high-pass filter series-connected between an audio input signal and a series-connected rectifier and integrator the output of which is connectable to the control input of a variable gain device that processes the audio input signal. A characteristically -10 db/decade amplitude versus frequency slope audio input signal is high-pass filtered, rectified and smoothed to produce a constant-energy, DC gain control signal. When the audio input signal is processed in accordance with the invention by the variable gain device to produce an audio output signal suitable for dynamic, downstream processing, the tonal balance and timbre of the audio input signal are preserved. Passive and active, half-order, five-stage high-pass filters are described that provide the desired +10 db/decade amplitude versus frequency slope over the audio frequency range.

Abstract: A surround processor adapted to apply a stereo surround processing and a monaural surround processing to audio input signals of two channels to provide surround processed outputs, wherein a stereo/monaural discrimination output based on inputted audio signals of two channels is caused to have a predetermined time constant to provide a mixture ratio control signal to change a mixture ratio between a stereo surround processing output signal and a monaural surround processing output signal, to thereby discriminate whether an input signal is a stereo signal or a monaural signal and to automatically carry out switching between the surround processing output. The time constant prevents switching between the stereo surround processing state and the monaural surround processing state from being suddenly conducted.

Abstract: A sound reproduction system for converting encoded stereo signals on input channels A and B into signals on left, supplemental left, right, and supplemental right output channels, respectively, that includes a left output channel for producing output signals intended to come from the left direction; a supplemental left output channel for producing output signals similar in level (intensity) to output signals of the left output channel and with reduced steered signal level for left direction signals; a right output channel for producing output signals intended to come from the right direction; and a supplemental right output channel for producing output signals similar in level (intensity) to output signals on the right output channel and with reduced steered signal level for right direction signals.

Abstract: An FM stereophonic receiver for receiving FM stereophonic broadcast signals, which includes a first comparison circuit for generating a first control signal corresponding to ratio of a left stereo signal (L) to a right stereo signal (R), a first separation circuit for separating the first control signal into a left dominant signal and a right dominant signal, a second comparison circuit for generating a second control signal corresponding to ratio of a stereo sum signal (L+R) to a stereo difference signal (L-R), a second separation circuit for separating the second control signal into a sum dominant signal and a difference dominant signal, a first level control circuit for controlling an output signal level of a stereo multiplex circuit through employment of the left and right dominant signals and the sum and difference dominant signals, a level detection device for detecting level of the second control signal, and a second level control circuit for controlling level of the difference dominant signal accordin

Abstract: There is disclosed a sound field correcting apparatus for adding indirect sound signals to audio signals from a decoder when a steering emphasis operation is not executed in a decoder and for limiting the addition of the indirect sound signals when the steering emphasis operation has been performed by the decoder. Thus, a reproduction sound having a proper extent feeling and a movement feeling of a sound image is obtained in accordance with a scene of a video image.

Abstract: An FM stereo receiver for receiving FM stereo broadcast signals includes a pro-logic surround system in which the left stereo signal, a right stereo signal, a stereo sum signal and a stereo difference signal are selectively emphasized. Also includes a noise signal detector for detecting the noise signal in the received signal, and a device for disabling the pro-logic surround system when the noise signal is detected.

Abstract: A reverberation circuit comprises an amplifier, attenuation circuit, a feedback component, and a delay circuit. The amplifier, delay circuit, and feedback component form a feedback loop. The amplifier amplifies an input signal supplied to an input terminal and outputs an amplified signal to the delay circuit. The output of the delay circuit is fed through a feedback component back to the amplifier. The feedback component controllably varies the feedback amount of the delayed signal to the amplifier in accordance with the desired depth of reverberation. An attenuation circuit is placed in the feedback loop, or before or after the feedback loop. The attenuation circuit selectively attenuates the level of specific frequency component of a signal passing therethrough whose frequency may be different depending on the depth of reverberation or feedback amount.

Abstract: The decoder of this invention decodes at least two channel signals in a directional information system where one or more input signals containing directional information have been encoded into the two or more channel signals. The decoder generates a first control signal substantially proportional to the logarithm of the ratio of the amplitudes of two of the channel signals to detect, as between two of the channel signals, whether the amplitude of one signal dominates that of the other. The decoder also generates a second control signal substantially proportional to the logarithm of the ratio of the amplitudes of the sum and the difference between two of the channel signals to detect the dominant signal in terms of amplitude. The decoder includes a matrix means responsive to the two or more channel signals and the two control signals for generating a number of output signals according to an algorithm.

Abstract: The invention provides surround mode stereophonic reproducing equipment for using the Dolby surround mode and another surround mode other than the Dolby mode by means of selectively switching between them. The equipment is provided with two front power amplifiers for driving front speakers on the right and left, and two rear power amplifiers for driving the rear speakers. The rear speakers are driven jointly by one of the rear power amplifiers while the center speaker is driven by the other power amplifier when using the Dolby surround mode, and the rear speakers are respectively driven by the two rear power amplifiers when using a surround mode other than the Dolby surround mode.

Abstract: The decoder of this invention decodes at least two channel signals in a directional information system where at least four input signals containing directional information have been encoded into the two or more channel signals. The decoder generates a first control signal substantially proportional to the logarithm of the ratio of the amplitudes of two of the channel signals to detect, as between two of the channel signals, whether the amplitude of one signal dominates that of the other. The decoder also generates a second control signal substantially proportional to the logarithm of the ratio of the amplitudes of the sum and the difference between two of the channel signals to detect the dominant signal in terms of amplitude. The decoder includes a matrix means responsive to the two or more channel signals and the two control signals for generating a number of output signals according to an algorithm.

Abstract: A television receiver includes a volume control circuit (4) for controlling levels of sound signals corresponding to a left channel, a right channel, a center channel and a surround channel and speakers (6 to 10) corresponding to these channels. The television receiver further comprises a test tone circuit (11; 18), a microcomputer (14) and a character display circuit (16). The test tone circuit (11; 18) supplies a test tone of a prescribed frequency sequentially to the speakers (6 to 10) through the volume control circuit (4). The microcomputer (14) provides a command to the character display circuit (16) so that a CRT 17) displays which speaker is currently supplied with the test tone as well as volume levels of the respective speakers.

Abstract: An interface circuit for inclusion in the control signal path of a variable matrix decoder wherein the attack and decay time constants imposed on said control signals may be varied by means of an auxiliary circuit which responds to the total signal level applied to the decoder and to sudden changes thereof, thereby improving the dynamic performance of the variable matrix decoder.

Abstract: A surround-decoder comprises terminals to which left and right stereo input signals are applied, a decoder for processing the left and the right stereo input signals to provide left and right stereo output signals, a center output signal and a surround output signal, circuits for detecting the left and the right stereo input signals to be monaural signals, and a switch responsive to an output signal of the detecting circuit for cutting off an output of a surround signal from the decoder.

Abstract: Decoding apparatus is disclosed providing desirable multichannel separation among various signals received in a channel pair and distinguished by relative phase and amplitude, including re-distribution of output vs. input signal nulls or positions on the "phase-amplitude sphere." Disclosed separation enhancement circuits are characterized by improved economy and signal purity. Enhancement is preferably controlled within the circuit by combination of gain-controlled enhancement signals with fixed matrix signals in summing amplifiers or the like. In some embodiments the enhancement signal for one output channel is modified to produce a different enhancement signal for a different output channel. In such separation enhancement, alternatives to the preferred-embodiment variable-gain element may include such commercial devices as expander or noise-reduction chips.

Abstract: A directionality enhancement system for converting encoded stereo signals on input channels A and B into four signals on left, center, right and surround output channels.

Abstract: By a method and a circuit for the purpose of decoding four-channel signals coded in a matrix and available in the form of a two-channel signal, whereby in each channel an automatic control of the amplification will take place by means of an output amplifier (.DELTA.L, .DELTA.R, .DELTA.B, .DELTA.C) in the output stage in question, it is proposed that the differential signal is conducted both to a delay circuit (.DELTA.T) and then to an expander circuit (EXP), and also to a central rectifier element (D1), that the output signal (U.sub.CD) form the rectifier circuit (D1, C.sub.A, C.sub.D) is both conducted to the expander circuit (EXP) and applied for controlling the channels in pairs, whereby the stereo channels are controlled in phase and the center and background channels in reversed phase of the mean value (U.sub.CD) of the differential signal, and that all channels moreover adjusted both in phase to the DC component of the summation signal amplitude and also in accordance with a level chosen in advance.

Abstract: The present invention provides a multi-channel stereo reproducing apparatus which can reproduce a recording medium such as an audio disc or the like in which in order that users can enjoy screen musics or the like reproduced at, for example, a concert hall and a movie theater.

Abstract: The decoder of this invention decodes at least two channel signals in a directional information system where at least four input signals containing directional information have been encoded into the two or more channel signals. The decoder generates a first control signal substantially proportional to the logarithm of the ratio of the amplitudes of two of the channel signals to detect, as between two of the channel signals, whether the amplitude of one signal dominates that of the other. The decoder also generates a second control signal substantially proportional to the logarithm of the ratio of the amplitudes of the sum and the difference between two of the channel signals to detect the dominant signal in terms of amplitude. The decoder includes a matrix means responsive to the two or more channel signals and the two control signals for generating a number of output signals according to an algorithm.

Abstract: Decoding apparatus is disclosed providing desirable multichannel separation among various signals received in a channel pair and distinguished by relative phase and amplitude, including re-distribution of output vs. input signal nulls or positions on the "phase-amplitude sphere." Disclosed separation enhancement circuits are characterized by improved economy and signal purity. Enhancement is preferably controlled within the circuit by combination of gain-controlled enhancement signals with fixed matrix signals in summing amplifiers or the like. In some embodiments the enhancement signal for one output channel is modified to produce a different enhancement signal for a different output channel. In such separation enhancement, alternatives to the preferred-embodiment variable-gain element may include such commercial devices as expander or noise-reduction chips.

Abstract: A system for receiving a plurality of audio input signals encoded with sound directions drives a plurality of loudspeakers which are physically arranged to generate apparent sound images in relation to encoded sound directions. The encoded input signals are analyzed for determining whether one encoded sound direction exceeds a predominance threshold with respect to other encoded sound directions. Logic control signals are generated for indicating directionality of predominant sound directions. In response to generated logic signals, the directional stability of the apparent sound images is enhanced.

Abstract: A directional enhancement system for quadrophonic sound systems wherein the improvement comprises an automatic dimension control. The automatic dimension control utilizes a plurality of limiting devices, each of which has an input terminal, an output terminal and a control terminal and is operative to limit the voltage at its output terminal to the lesser of the voltages appearing at its input terminal and its control terminal. The dimension control can also be operative to limit the maximum values of the directional control signals generated and their sums to a voltage controlled by the user of the system thereby limiting the amount of directional enhancement provided by the system.

Abstract: The disclosed invention relates to directional enhancement systems and provides apparatus for enhancing the directional content of information contained in a plurality of composite signals derived from preceding decoding apparatus of the system. The apparatus of this invention includes a plurality of limiting devices equal in number to the number of control signals provided in the processor of the directional enhancement system. Each one of the plurality of limiting devices has an input terminal connected to a different one of the control signal outputs of the processor, a control terminal and a control device having an input coupled to a variable control voltage source and an output coupled in common to all of the control terminals of said limiting device. The apparatus of this invention limits any control signal which may be developed in the processor to a value less than or equal to that which would obtain in the absence of the dimension control apparatus of this invention.

Abstract: A decoder is provided for feeding an irregular array of m (being three or more) pairs of diametrically opposite loudspeakers, each loudspeaker being disposed at an equal distance r from a common reference point. The decoder incorporates a WXY circuit 10 for producing output signals W, X, Y and -jW from the input signals, and shelf filters 12, 14, 16 and 22 and high-pass filters 18, 20 and 24 for producing output signals W', X', Y' and -jW.sub.i.sup.". In addition the decoder includes an amplitude matrix circuit 26 for producing signals S.sub.i.sup.+ and S.sub.i.sup.-, to be fed to the loudspeakers of each pair, which satisfy particular gain requirements, whereby the outputs of the loudspeakers are adapted to irregular positioning of the loudspeakers which may be dictated by room geometry. A decoder is also provided for feeding a three-dimensional loudspeaker layout.