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The Application of Mid-Side Theory to Produce Analog Stereo Audio Records Using a Single Laser Beam

The recent resurgence of vinyl music records sales led by a consumer demand is increasing faster than production capability. This has resulted in supply delays across the sector. Thus far, manufacturing investments have been focused on traditional proven methods rather than alternative technologies. This paper demonstrates for the first time the production of a stereo recording via analog methodology using a single pulsed laser beam. Using mid-side theory, to combine a sum (mono) signal with a difference signal, a 532nm Nd:Yag laser beam was used to process high-impact polystyrene discs (HIPS). Stereo recordings were manufactured by varying the laser power to produce a difference signal and deflecting the beam with a mirror mounted galvanometer to produce the sum signal. Upon playback on a conventional turntable, the recordings were analyzed with an oscilloscope and stereo separation was observed. To our knowledge this is the first time a stereo signal has been successfully recorded using a single laser beam. Previous literature has used a single laser beam to achieve mono signals and required significant digital pre-processing of the audio source. This new methodology requires lower investment costs than traditional pressing plants and would make volume-tailored production more affordable.

JAES Volume 68 Issue 4 pp. 273-283; April 2020
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AES - Audio Engineering Society