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I wonder how that worked with pits.
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I was intrigued by the same question so I studied my Luxman D408 (D408 = Pioneer CLD-900) player's schematics and technical whitepaper. I don't get it 100% but here's how I think it works: The pits fly by on the LD and are "read" by the pickup not as bits, per se, but an RF signal around 3 MHz (If one were to read an RF signal from a CD the same way, I think it would be around 1.5Mhz). That signal carries both FM audio and video (see below). The audio is very near in frequency to the video- they didn't have a lot of bandwidth to play with- so it's filtered by a bandpass filter in the video section, then goes to the audio board where it passes through a sharp lowpass filter around 4Mhz to cut out the video. The cleaned-up FM signal goes to a Phase-Shift Discriminator which converts changes in the FM signal frequency to phase shifts and detection is by what looks to me like an old TV quadrature detector (read below). It's not a phase-locked-loop or anything that sophisticatd. Quadrature has a decent performance capability and we hear that in the decent audio performance of LD's, eh?
The limited bandwidth limits separation of the L and R FM signal to only .5 so Mhz, which in turn limits the audio bandwidth to that similar to broadcast FM, I'm not sure but it sounds that way. Decent analog circuitry following the detector is probably the Achilles heel of most LD players. I chose my Luxman LD player on the basis of it having a smooth, sweet sound primarily, which I attribute to their attention to smooth, sweet analog circuitry.
Technical experts please correct my misunderstandings!
The LaserDisc used an encoding scheme similar to PWM where the width of the pits and lands resulted in an analog video signal which then contained modulated analog audio.
Analog frequency modulation to be precise.
My full-spectrum, frequency modulated optical analog disk format may one day be a reality.
The Optigan optical organ: (totally not laser, but a cool trick)
Edits: 10/15/16
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