Over the years, Herbie's Audio Lab has sold many thousand grungebuster CD mats and tens of thousands of The Black Hole CD mat. Customers who have bought and are using these mats have enthusiastically sang their praises.
I'm not sure whether Herbie's Audio Lab CD mats directly affect the laser's reading of digital data. I believe reducing micro-vibrations in CD spin has great potential for reducing laser-reading error, though. Unlike data CDs that have redundant binary error correction, audio CDs rely on algorithm-based "guessing." It seems reasonable to assume that a reduction in reading error would result in a more perfect sonic reproduction.
Our CD mats reduce micro-vibrations in the CD spin, primarily at the clamping puck/disc interface. These micro-vibrations permeate through the clamping mechanism and dissipate throughout the player, causing distortion and microphonics in capacitors, op-amps and other sensitive electronics, primarily in the digital-to-analog and output stages.
Whatever the sum reason for Herbie's CD Mats to achieve sonic improvement, it primarily boils down to micro-vibration reduction. I believe that other kinds of CD mats, Marigo, Millennium, etc., probably achieve a major portion of their benefit, if not all, by easing micro-vibrations generated by the CD spin.
Do you really need a CD mat, though? Not really.
A CD mat is sort of a "quick-fix" attempt at solving a larger overall problem: isolation and vibration control of the component as a whole.
Isolating a CD player or transport with a whole approach will generally accomplish what a CD mat does and then some. Using Tenderfeet in place of the factory feet is the first place to start, then a SuperSonic Stabilizer or two on top to relieve chassis vibration. (If external DAC is used, isolating the DAC would have a major priority.)
Internally, applying rope caulk (Mortite, etc., but not white rope caulk) is extremely beneficial. Rope caulk is not like other caulks, but is like a putty or clay that you can knead by hand and press into place. Apply some liberally to the underside of the component lid and along the sides. Also around circuit board mounts, motor mounts, wiring terminals, where practical. This material (available at most any hardware store) is inexpensive and very effective; it's sonically neutral and highly efficient at absorbing micro-vibrations. I applied rope caulk to my Lambda transport about seventeen years ago and, although not quite as soft and pliable as when first applied, it's still perfectly functional and appears exactly as the day it was pressed into place.
Permatex Blue RTV Silicone Gasket Maker (available at auto parts stores) is also beneficial, very neutral sonically and a super micro-vibration insulator. Use it sparingly on capacitors and microprocessors.
To complete this "wholistic" approach to damping, HAL-O JR interconnect dampers on the cable plugs will inhibit harmful vibrations from transferring to and from the component. This, of course, implies that the system as a whole, not just the CD player, must be up to par to realize a CD's potential.
Of course not everybody is willing to go through so much work just to get a more enjoyable listening result from their CD, SACD, or DVD player. Some people just like to use what they have "right out of the box." In that case, CD mats can be the cat's meow for a more involved listening experience.
And if you should have a thoroughly isolated player, CD mats, although you might not really "need" them, can be beneficial and fun to play with. Some CDs, especially older ones from the earlier days, aren't mastered quite perfectly, and a mat might help to ease some of the glare and irritability. You might find some CDs that just blossom with The Black Hole or grungebuster Black CD Mat on them, others not. Newer CDs that are a little over-compressed tend to come to life with the improved resolution of low-level information.
What many people find pleasantly and profoundly surprising with better micro-vibration control is the music becomes much more analog-like and realistic, more like the live/real event. A lot of the "digititis" and glare commonly blamed on the digital format itself is actually distortion caused by micro-vibrations and microphonics in the electronics that is not mastered into the CD itself.
I've found out-of-the box CD play to be generally quite lacking in sound quality compared to vinyl and studio tape. With clean, conditioned electricity, good cables, and micro-vibration isolation, however, a good quality player (especially a competently modified one) can reveal CD recordings very close to or as good as vinyl. And without the frequent pops and crackle of vinyl, sometimes even more enjoyable to listen to. Much of today's digital music is very well mastered and capable of producing a superb listening experience for even the most discerning listener--but it usually ain't gonna happen with a system that's just right "out of the box."
SteveHerbie's Audio Lab