Microphone system for producing signals for quadraphonic reproduction

Apparatus for producing first and second composite signals the first of which comprises the sum of a predominant left-front (LF) signal component and subdominant left-back (LB) and right-back (RB) signal components and the second of which comprises the sum of a predominant right-front (RF) signal component amd said subdominant LB and RB components and in which the LB and RB signal components in one of said channels lead and lag, respectively, the LB and RB signal components in the other of said channels by a predetermined differential phase-shift angle, said apparatus comprising:

• means including an array of at least four microphones in close proximity to each other for producing, when disposed within a field of surround-sound sources of sound, four signals each defined by a predetermined limacon sensitivity pattern having the equation E= + (1-k)cos.theta.whose directions of maximum sensitivity are oriented at different predetermined azimuthal angles relative to a reference direction, wherein k is a constant having a value less than one, .theta. is the angle between said reference direction and the axis of maximum sensitivity of each microphone, and E is the normalized amplitude of the voltage produced by an incident sound wave of unity pressure,
• means for shifting the phase of a first of said four signals relative to a second of said four signals by a predetermined phase angle and combining said phase-shifted first and second signals to produce said first composite signal, and
• means for shifting the phase of a third of said four signals relative to the fourth of said four signals by a predetermined phase angle and combining said phase-shifted third and fourth signals to produce said second composite signal.