The Schoeps OCT Set Surround Front System is a microphone set designed for the front surround channels. OCT (Optimized Cardioid Triangle) is a method for picking up the 3 front chan¬nels of a surround recording. It can be combined with any of the several methods used for obtaining the rear channels, thus completing the OCT surround.
The preferred setup for OCT uses a forward-facing cardioid for the center channel. For the front L and R channels, 2 supercardioid microphones are placed at the opposite ends of an imaginary line running about 3.14” (8cm) behind the center microphone. These 2 microphones should be 15.74 to 35.43” (40 to 90cm) apart, depending on the required recording angle. They must face squarely outward, away from the center. This method achieves a good separation between the center-to-left sector and the center-to-right sector to give sound clarity.
The entire process of placing the microphones at optimal distance and alignment helps prevent the formation of annoying ‘phantom images’ of sound sources in the wrong sector during playback. A clean center channel is conveyed by this system since front-incident sound is picked up mainly by the cardioid in the center. The left and right microphones, with their high directivity, pick up front-incident sound only at a much lower level.
If the cardioid is placed 3.14” (8cm) forward, the following recording angles will result, depending on the distance between the supercardioids.
15.74” (40cm): 160°
19.68” (50cm): 140°
23.62” (60cm): 120°
27.55” (70cm): 110°
31.49” (80cm): 100°
35.43” (90cm): 90°
It is better to err in the direction of greater spacing so as to avoid center-heavy images. As the supercardioids receive maximum of their sound from off axis necessitates, the use of small-diaphragm condenser microphones with the requisite independence of frequency response from the angle of sound incidence is preferable. The CCM 41V, MK 41V, CCM 41, and MK 41 can be used with this set up.