Abstract: A frequency-dependent linear audio signal processor takes source signals S in input signals and provide directionally spread directionally encoded output signals. The processor directionally encodes with constant gain magnitude frequency components of the source signal S to-and-fro across a predetermined directional stage P" as frequency increases such that at least three predetermined positions within the stage P", the directional encoding has substantially zero perceived phasiness. The processor may be a frequency-dependent rotation matrix for stereo input signal and may be a unitary network using a feedback path around parallel identical all-pass networks in series with a rotation matrix and a feedforward path bypassing the all-pass networks. Successive frequencies of positioning of source signal S at a predetermined position P within the stage P" are preferably spaced approximately uniformly on a logarithmic or Bark Frequency scale.

Abstract: 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.

Abstract: 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.