Michael A. Gerzon

Audio signal processor providing simulated source distance control

An audio signal processing system produces an output 24 having an illusory distance effect for a sound source signal S by feeding it via a direct signal path 25 and an indirect signal path 22, 23 passing through early reflection simulation apparatus 1 which feed an output mixing mechanism 9. A control system adjusts the relative delays 3, 4 and relative gains 5, 6 in the direct 25 and indirect 22, 23 signal paths to modify the illusory distance effect so as to substantially maintain the mathematical relationship between the gains and time delays of simulated reflections relative to first sound arrivals at the output 24 encountered for sounds at that source distance in actual rooms. Signal paths 22, 23, 24, 25 may be stereophonic or multichannel using matrix gain coefficients in the early reflection simulator 1, and may produce different simulated distances for different sound positions. A plurality of sound sources S may have different simulated distances while feeding a common early reflection simulator 1.

Sound reproduction system having a matrix converter

Matrix reproduction decoding means derive from input signals intended to feed a stereophonic plurality of loudspeakers output signals intended to feed a second greater plurality of loudspeakers in a stereophonic arrangement covering a sector of directions, substantially so as to preserve total reproduced energy to within an overall gain and equalization, and to preserve to within constants of proportionality the angular dispositions of reproduced acoustical velocity and sound intensity vectors at an ideal listening position. Preferably for two-channel signals matrix means is frequency-dependent giving increased angular width above 5 kHz, and may incorporate width control. Matrix means encoding loudspeaker feed signals into transmission channel signals, and matrix means decoding transmission channel signals into loudspeaker feed signals may be used giving overall matrix means in accordance with the invention. Matrix means may be used to provide improved directional matching of sounds and associated visual images.

Maximum directivity factor of nth‐order transducers

It is proved using general group‐theoretic and Hilbert‐space methods that the maximum directivity factor obtainable from an nth‐order directional acoustic transducer is (n+1)2, that this most directional transducer is axially symmetric, and that its polar response to sounds arriving from an angle ϑ off axis is proportional toJn/k=0 (2k+1) Pk(cosϑ). Subject Classification: [43]85.40, [43]85.62.It is proved using general group‐theoretic and Hilbert‐space methods that the maximum directivity factor obtainable from an nth‐order directional acoustic transducer is (n+1)2, that this most directional transducer is axially symmetric, and that its polar response to sounds arriving from an angle ϑ off axis is proportional toJn/k=0 (2k+1) Pk(cosϑ). Subject Classification: [43]85.40, [43]85.62.

Hierarchical Transmission of Multispeaker Stereo

Introduction of the apparent localisation of sound images than conventional 2-speaker stereo, especially when sounds must match visual images in direction. This paper describes methods of optimising subjective reproduction from larger numbers n = 3 to 5 of front-stage speakers based on theoretical models for subjective sound localisation, whereby sounds intended for reproduction via n1 stereo speakers are optimally reproduced via a larger number n2 of loudspeakers, and a compatible hierarchy of n-speaker stereo transmission standards is described.

Sound reproduction system with matrixing of power amplifier outputs

In a surround sound reproduction system the required number of power amplifiers is reduced by effecting at least part of the decoding operation by the manner in which the various loudspeakers are connected to the outputs of the power amplifiers while preserving linear independence of the signals fed to every set of three loudspeakers. In one embodiment, the loudspeakers are grouped in pairs such that the sum of signals fed to the loudspeakers of each pair is the same for all of the pairs, a first amplifier is arranged to receive said signal and a respective second amplifier for each pair of loudspeakers is arranged to receive the signal to be fed to one of the loudspeakers of such pair, the second loudspeaker of each pair being connected between the output of the corresponding second amplifier and the output of the first amplifier. In another embodiment, the number of loudspeakers is one greater than the number of power amplifiers, one loudspeaker is connected between earth and a common terminal and the other loudspeakers are connected between the common terminal and the output of a respective amplifier.