Saturday, February 28, 2009

Laser turntables for your vinyl LPs

Hi All,

Friends who know of my interest in audiophilia (ok... look it up if you think it's something perverted) have asked me on several occasions "Why aren't there turntables that use lasers instead of needles" to play vinyl LPs? That seems like a logic question... almost a no-brainer for engineers who have seen lasers take over audio playback of digital compact discs. Why not user lasers for analog audio reproduction? I had read of laser turntables in the past, but for some reason they never got well established. I never really understood why, other than cost.

The March 2009 issue of IEEE Spectrum magazine provides the answers, in an article titled "Give Your Records a Break". Yes, price is a big factor, with laser LP players from ELP Corp priced in the range of $15,000! But there are also fundamental technical reasons holding back lasers from replacing diamond needles, and they may seem to be somewhat counter-intuitive.

It turns out that lasers are just TOO good at tracking the undulating grooves of a vinyl LP. Phono cartridges have limited bandwidth from mechanical as well as electrical limitations, whereas lasers can pickup every little spec of dust and scratch in the vinyl surface. Many of these defects are too small to move a magnetic stylus. To get acceptable sound quality from a laser turntable, an expensive record cleaner is mandatory as a minimum, and an additional signal processor to filter out noise is needed to really cleanup the signal. That's a lot of trouble to go to and, ironically... it puts digital signal processing back in the chain of sound reproduction!

As I've written before (see Digital vs. Analog: never-ending myths of CDs vs. LPs)
, I have no problem with those audiophiles who prefer the sound of LPs. I do have a problem with those who are compelled to claim that defects in digital CDs prevent them from sounding as good as LPs. (See Audio Mythology). All too often pseudoscience, and technically flawed arguments, are used by the vinyl snobs. So I think it is fascinating to learn that the laser (actually 5 lasers in the ELP system), while eliminating the limitations of the standard magnetic pickup, ends up producing sound that is unacceptably revealing of vinyl flaws.


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