A specific type of baffled stereo miking technique based on use of high quality omnidirectional microphones. Inventor Jorg Jecklin, the former chief sound engineer of Swiss Radio, was impressed by the spatial qualities of binaural recording but he tried to find ways to overcome the necessity of small-diaphragm cardioid microphone use. So he replaced binaural recording’s artificial head with a 12” disc of about 3/4” thickness, which had a muffling layer of soft plastic foam on each side. Then he took two free-field equalized omnidirectional mics and attached them to the disc in such a way that the disc was between them. The capsules were above the surface of the disc just in the center, 17 cm apart from each other and each pointing 20 degrees outside. The result was an amazingly well defined stereo image, with true side separation and natural sounding depth. Jecklin began referring to this as an “Optimal Stereo Signal” (OSS). Almost every Swiss studio, and many others in Europe, uses an OSS disc for at least some stereo recording. Experiments with smaller-diameter discs proved unacceptable.