Abstract: A method derives at least three audio signals, each associated with a direction, from two input audio signals. In response to the two input signals, a passive matrix generates a plurality of passive matrix audio signals, including two pairs of passive matrix audio signals, a first pair of passive amtrix audio signals represent directions lying on a first axis and a second pair of passive matrix audio signals represent direction lying on a second axis, the first and second aces being substantially at ninety degrees to ach other. The pairs of passive matrix audio signals are processed to derive a plurality of matrix coefficients therefrom, The processing includes deriving a pair of intermediate signals and urging each pair of intermediate signals toward equality in response to a respective error signal. At least three output signals are produced by matrix multiplying the two input signals by the matrix coefficients.

Abstract: A multidirectional audio decoder using an “adaptive” audio matrix derives at least one of a plurality of output audio signals from two or more directionally-encoded audio input signal streams (S1(?), S2(?), . . . SN(?), wherein ? is the encoded angle of a source audio signal. Each output signal is associated with a principal direction ?. In order to generate each output signal, a pair of intermediate signals (“antidominant” signals) are generated, constituting the antidominant signal for each of the two adjacent principal output directions of the decoder. The antidominant signal for any arbitrary principal (or “dominant”) direction is the combination of input signals having coefficients such that the combination goes to zero for that dominant direction. Amplitude control is applied to the two antidominant signals to deliver a pair of signals having substantially equal magnitudes that are additively or subtractively combined to provide the output audio signal associated with a principal direction.

Abstract: Various equivalent adaptive audio matrix arrangements are disclosed, each of which includes a feedback-derived control system that automatically causes the cancellation of undesired matrix crosstalk components in the matrix output. Each adaptive audio matrix arrangement includes a passive matrix that produces a pair of passive matrix signals in response to two input signals. A feedback-derived control system operates on each pair of passive matrix signals, urging the magnitudes of pairs of intermediate signals toward equality. Each control system includes variable gain elements and a feedback and comparison arrangement generating a pair of control signals for controlling the variable gain elements. Additional control signals may be derived from the two pairs of control signals for use in obtaining more than four output signals from the adaptive matrix.

Abstract: A method derives at least three audio signals, each associated with a direction, from two input audio signals. In response to the two input signals, a passive matrix generates a plurality of passive matrix audio signals, including two pairs of passive matrix audio signals, a first pair of passive amtrix audio signals represent directions lying on a first axis and a second pair of passive matrix audio signals represent direction lying on a second axis, the first and second aces being substantially at ninety degrees to ach other. The pairs of passive matrix audio signals are processed to derive a plurality of matrix coefficients therefrom, The processing includes deriving a pair of intermediate signals and urging each pair of intermediate signals toward equality in response to a respective error signal. At least three output signals are produced by matrix multiplying the two input signals by the matrix coefficients.

Abstract: A surround sound processor system for multichannel redistribution of stereophonic signals has digitally controlled gains in each input and each output channel, controlled by a microprocessor, which receives an input signal from a microphone placed at the preferred listening location within the listening area for automatically balancing the input signals and setting both input and output gains during a calibration process so as to provide the listener with the best possible surround sound reproduction of the stereophonic source material. As a visual aid, the microprocessor displays menus and messages on a video screen, and a visual display shows the relative levels of the six axes of control signals within the surround sound processor.

Abstract: A surround sound processor for presenting stereophonic audio signals on a number of loudspeakers surrounding a listening area, comprising an input matrix stage, a detector filter and matrix circuit, a direction detector circuit incorporating improved filters, a novel detector splitter circuit providing three direction signals from the two direction detector circuit outputs, a novel three-channel servologic circuit with improved variable filters responding selectively to the rates of change of the direction signals and providing six control voltage signals through linearity correction networks to six voltage-controlled amplifiers, the outputs of which are combined in an output matrix to provide a number of loudspeaker feed signals through buffer amplifiers to the output terminals of the processor. The detector splitter circuit is configurable to either a forward oriented or a backward oriented mode of operation, corresponding changes being made to the voltage-controlled amplifiers and output matrix circuitry.

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: A surround sound processor for presenting stereophonic audio signals on a number of loudspeakers surrounding a listening area, comprising an input matrix stage, a detector filter and matrix circuit, a direction detector circuit incorporating improved filters, a novel detector splitter circuit providing three direction signals from the two direction detector circuit outputs, a novel three-channel servologic circuit with improved variable filters responding selectively to the rates of change of the direction signals and providing six control voltage signals through linearity correction networks to six voltage-controlled amplifiers, the outputs of which are combined in an output matrix to provide a number of loudspeaker feed signals through buffer amplifiers to the output terminals of the processor. The detector splitter circuit is configurable to either a forward oriented a backward oriented mode of operation, corresponding changes being made to the voltage-controlled amplifiers and output matrix circuitry.

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: 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 means 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 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 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 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: A method and apparatus for generating control voltage signals in a surround sound processor is disclosed which utilizes a on-shot monostable multivibrator for minimizing intermodulation distortion while following rapid directional change yet minimizing intermodulation distortion. The apparatus includes means 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 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 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 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 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.