Jecklin disk

This technique was invented by Jürg Jecklin, the former chief sound engineer of Swiss Radio and teacher at the University for Music and Performing Arts in Vienna.

It is a refinement of the baffled microphone technique for stereo initially described by Alan Blumlein in his 1931 patent on binaural sound.

Jecklin's German from his script: "Zwei Kugelmikrofone sind mit einem gegenseitigen Abstand von 36 cm angeordnet und durch eine mit Schaumstoff belegte Scheibe von 35 cm Durchmesser akustisch getrennt.

"[1] The effect of the baffle is to introduce some of the frequency-response, time and amplitude variations human listeners experience as positioning cues, but in such a way that the recording also produces a useful stereo image through loudspeakers.

There are multiple variations of this technique, with "discs" of varying sizes and shapes, all of which work to some degree in helping to create a recording with a more believable stereo "image" than a spaced pair of microphones, but the size of the barrier is critically related to the lowest frequency at which it operates.