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In Reply to: Idea to test if painting back side and edges of CD has an effect on data posted by La Grenouille on February 09, 2001 at 15:07:05:
I don't thing it has anything to do with missing codes. I thing it has to do with a good clean signal coming back to the photo diodes and a cleaner RF signal from that. If you look close at a Cd you'll see through it. The mirror is not 100%, not even close. A lot of laser light gets into the inside of the CD. There it bounces around off all those bumps, the pits from the other side. and it get back out through the same bad mirror it came in through. Now, the laser is red, and with a Green (green the opposit of red) pen we paint out CD around and over the top, and the clear center on both sides. The laser light now run into this green and doesn't come back out. The result, clearner signal from the photo diodes, better RF and a better sounding unit! Now, what is so out of this world about that? Here at the lab we have no problem with people understanding it. Even my ex wife hears it! bobwire
Follow Ups:
bobwireI know you use a green pen, but if the audible improvement, which I also believe is obviously apparent, is due to flare (ambiant light), I would think black could be more effective. The reason I say this is I used to operate a copy camera for years in the printing business. We would often have to filter out specific colors for various reasons. The exact shade of the filter we used had a lot to do with the sucess of the effect we were trying to achive. In other words, theoretically if you had the exact opposite shade of green from the exact shade of red it would absorb all the red. Black however, absorbs all shades and colors of light very effectivly. Also I have gone into many shops and greatly improved the quality of the lithography by simply painting the walls, floors, and ceilings black in the room where the copy camera was located, and turning off the overhead lights when taking the actual shot. I think a similar thing is happening with the tweaked CDs, I hear the biggest improvement in the smoothness of the sound, less harsh.
twystd
You may have different results than I, but black around outer edge was not as good as green. Sanding edges seems to help. Black on inner edge OK, w/ green around outer edge; here's something else to try on outer edge sometime - violet pen in four equally spaced one-inch marks. There really are so many things that can (and should) be done, it gets kind of ridiculous. The whole is > sum parts...
bobwire wrote:I don't thing it has anything to do with missing codes. I thing it has to do with a good clean signal coming back to the photo diodes and a cleaner RF signal from that.
That would be all well and good if what we were listening to is the signal coming off the photodiodes. But that's not what we listen to.
The signal comes off the photodiodes as an analog signal which is then run through an A/D converter which produces the digital information that's then buffered, demodulated, deinterleaved, run through error detection/correction/interpolation, etc. If there weren't a sufficiently clean signal coming from the photodiodes, it would result in data errors from the A/D converter.
The CD optical system is rather immune to noise. The depth of the pits corresponds to 1/4 wavelength of the laser's wavelength in the polycarbonate medium. That means that when the light reflects from the pit, it has a very high contrast compared to the light reflecting off the lands since its now polarized 180 degrees out of phase with the light reflecting off the lands (90 degrees into the pit and 90 degrees back out).
If you look close at a Cd you'll see through it. The mirror is not 100%, not even close.
It doesn't have to be due to the high contrast ratio mentioned above.
A lot of laser light gets into the inside of the CD. There it bounces around off all those bumps, the pits from the other side. and it get back out through the same bad mirror it came in through.
But its angle of incidence will tend to vary randomly from the incidence of the main beam so very little if any will ever find its way back to the photodiodes to cause any problems.
Now, the laser is red, and with a Green (green the opposit of red) pen we paint out CD around and over the top, and the clear center on both sides. The laser light now run into this green and doesn't come back out.
This is just pure myth. The laserdiodes operate in the NEAR INFRAred. Not VISIBLE red. Green ink will not absorb the 780nm light from the laserdiodes used in CD players.
The result, clearner signal from the photo diodes, better RF and a better sounding unit!
So how exactly does the "cleaner signal from the photo diodes" become "better sound"? Remember, we're not listening to the output from the photo diodes. So you need to make the connection.
Now, what is so out of this world about that?
You mean other than it being grossly oversimplified and in one instance factually incorrect?
se
Better signal from the photo diodes gives a better sound because the EYE-pattern is cleaner. Less jitter. That is also why I tell folks to regulate the 5 volts going to the laser unit, for a cleaner eye-pattern. And putting the RF on a coax goes right along with it. bobwire
bobwire wrote:Better signal from the photo diodes gives a better sound because the EYE-pattern is cleaner. Less jitter.
What jitter? Why is there this persistent (though wholly erroneous) notion that the data on the disc somehow goes straight from the photodiode output to the transmitter or DAC? The only reason I can think of is that people take grossly oversimplified explanations of how a CD works far too literally.
For example the animation at this site:
How Does a CD Player Really Work?
Certainly if CD players worked the way this demonstration shows, then you would have a case for jitter. But that's now how a CD REALLY works (in spite of the title of the article). Not by a long shot.
If you want to know REALLY how a CD player works, I'd recommend Ken Pohlmann's book Principles of Digital Audio . For a much more watered down (though freely available) version, the CDFAQ is about as comprehensive as I've found online.
But for anyone with more than just a passing interest in digital audio, Pohlmann's book is hard to beat.
se
Not all CDP lasers are infrared, and I think most aren't. I had a PDM-60 where the spindle motor stopped spinning. I took it apart to see if I could fix it. I had the whole assembly in my hand when I turned it on. I couldn't find how to get to the spindle motor, but I did see the laser-lens combo move up and down trying to lock on the pits. it was dim, but it was red.
kcisobderf wrote:Not all CDP lasers are infrared, and I think most aren't. I had a PDM-60 where the spindle motor stopped spinning. I took it apart to see if I could fix it. I had the whole assembly in my hand when I turned it on. I couldn't find how to get to the spindle motor, but I did see the laser-lens combo move up and down trying to lock on the pits. it was dim, but it was red.
I didn't say infrared. I said near infrared. This is the region that's just outside the visible spectrum above red. The visual spectrum runs from 400nm (violet) to 700nm (red) with blue, green, yellow and orange in between. The CD's based on a 780nm laser.
If the peak output of the laser diode were in the visible red, it wouldn't appear dim to you. It would look about as bright as looking into a red laser pointer (which are usually around 650nm). But the peak output is outside the normal visible spectrum and I'd guess the reason you saw anything at all is because the output of the laser is sufficient to overcome the extreme insensitivity our eyes have at that wavelength or the laser was outputting some small amount of energy at lower, more visible wavelengths.
se
Hi there! You say that the peak is in the near infrared, and that thereīs some visible red, too. That means sort of a gaussian distribution in the emission spectrum (something to expect, for these "laser emitting diodes" are not lasers really). From what I know about laser optics, the great difference the laser makes is, that laser light is extremely phase-coherent, ie all its energy is associated with a single wave front: that makes a laser beam not to open the same way as normal, non-coherent light does (I remember projecting a real, well collimated laser beam over a target more than 400 m. far, and the diameter of the beam, measured at the target, wasnīt more than 4% wider than the beam emerging from the collimating lense). This unique property makes lasers so useful in data transmission -Remember NASA experiments with a laser beam bouncing back from satellites?Wave coherent light (laser) is relatively easy to focus, and to recover when reflected on a surface; normal, non-coherent light isnīt. Maybe what the green paint does is just clean the reflected beam from non-coherent (red, visible) light, getting a better focused beam at the photodiode.
And re what somebody said about errors, that sounds to me as the old "bits are bits" song. Unfortunately, thatīs not quite true: if thereīs parasitic light, or if there are fluctuations (flutter) in the spinning CD, not all engraved bits can be read, as some will appear to the photodiode just in the limit of what can clearly be taken for a bit (itīs differences what the photodiode detects). Itīs there that error-correction mechanisms come to help.
An undeniable fact is, that not all CD players sound the same, even units using the same transport mechanism do sound very different from each other (we all know that some very expensive, and hughly praised machines use the same mechanics as other relatively inexpensive ones). So, everything you can do to have: a) a more stable mechanism, via better damping, b) a cleaner power supply, c) less jitter (better clocking helps here, too, and d) a cleaner optical signal (green paint, CD surface cleaning and polishing) must, and does, help at getting better sound. Then will come the DACs, analogue stages, cables,...
Sorry for being so long, and for saying so many obvious things, but I feel that, all together, make some sense, and put things in perspective.
orejones wrote:Hi there! You say that the peak is in the near infrared, and that thereīs some visible red, too. That means sort of a gaussian distribution in the emission spectrum (something to expect, for these "laser emitting diodes" are not lasers really).
Frank has already addressed this issue (yes, laser diodes really are lasers) so I won't comment further. When I spoke of being able to see some amount of visible light, I left it open to two possibilities. One, that there was some sideband output from the laser diode. That wasn't my first choice but I wasn't able to find any curves of spectral output for the laser diodes used in CD players so I wasn't certain enough of it to exclude it. Frank has addressed that issue as well.
Two was that the output from the laser diode was sufficient that one could perceive some light from it since our eye's sensitivity doesn't simply stop at a given wavelength but drops off at some finite rate at each end of the spectrum.
From what I know about laser optics, the great difference the laser makes is, that laser light is extremely phase-coherent, ie all its energy is associated with a single wave front: that makes a laser beam not to open the same way as normal, non-coherent light does (I remember projecting a real, well collimated laser beam over a target more than 400 m. far, and the diameter of the beam, measured at the target, wasnīt more than 4% wider than the beam emerging from the collimating lense). This unique property makes lasers so useful in data transmission -Remember NASA experiments with a laser beam bouncing back from satellites?
Yes, and you can get the same performance from laser diodes. For example those used in laser pointing devices. They are virtually the same as the laser diodes used for CD except that they lase in the visible red spectrum (usually either 630nm or 650nm depending on the laser diode).
Wave coherent light (laser) is relatively easy to focus, and to recover when reflected on a surface; normal, non-coherent light isnīt.
Yes, which is why CDs use lasers.
Maybe what the green paint does is just clean the reflected beam from non-coherent (red, visible) light, getting a better focused beam at the photodiode.
Perhaps it does. Wouldn't be difficult to determine that. But that's not really the issue in this thread.
And re what somebody said about errors, that sounds to me as the old "bits are bits" song.
With respect to data integrity (which IS the issue in this tread) bits IS bits. If the original data word is 0011010110100110 and you recover 0011010110100110, there is ABSOLUTELY ZIP, ZILCH, ZERO difference between them. NONE. They are EXACTLY the same data.
So as long as you are recovering the data off the disc without error, then all the green pens in the world will have ZIP, ZILCH, ZERO effect on data integrity except to possibly INTRODUCE unrecoverable errors.
And provided you have recovered the data off the disc without error, there are only two things which can possibly produce an audible difference at the output of the DAC chip. That is WHEN the data is converted (i.e. jitter) and how ACCURATE the resultant analog value is after conversion (i.e. nonlinearities in the converter).
And indeed there are many things downstream which can have an effect on both of those elements, but that's not the issue raised by the original poster which had to do with the integrity of the data read off the disc.
Unfortunately, thatīs not quite true: if thereīs parasitic light, or if there are fluctuations (flutter) in the spinning CD, not all engraved bits can be read, as some will appear to the photodiode just in the limit of what can clearly be taken for a bit (itīs differences what the photodiode detects). Itīs there that error-correction mechanisms come to help.
Yes. And as has been said (and demonstrated) the error detection/correction system is quite robust and I have not seen any evidence yet that green pens (or black pens for that matter) have any appreciable effect on the accurate recovery of data off the disc. There's plenty of speculation, but not even the folks who sell these tweaks have shown any evidence of it even though it can be done quite trivially.
An undeniable fact is, that not all CD players sound the same, even units using the same transport mechanism do sound very different from each other (we all know that some very expensive, and hughly praised machines use the same mechanics as other relatively inexpensive ones). So, everything you can do to have: a) a more stable mechanism, via better damping, b) a cleaner power supply, c) less jitter (better clocking helps here, too, and d) a cleaner optical signal (green paint, CD surface cleaning and polishing) must, and does, help at getting better sound.
Yes. But the issue here is data integrity. And many of the claims involving green pens and the like have to do with more accurately recovering the data from the disc. But so far no objective evidence of this has been brought forth in spite of the fact that it can be demonstrated quite easily.
Then will come the DACs, analogue stages, cables,...
And at which point we're well beyond the issue of data integrity off the disc.
se
How do you mean "this are nor really lasers" Are you saying there are led's in CD players? You are talking as if there is only one sort of laser, the "coherent collimated one, like nasa uses" . The coherence length of lasers can be from les than 1 mm to 10th's of km's, but they can all be laser. For most applications the coherence length is not that important, as it is for something like holography.
That you can see the laser is not because "they have red components" but because the of the relative high power combined with a low but real sensitivity of the human eye (even above 800 nm you see a laser with sufficient power). The linewidth of the laser of a cd played is only a few tenth's of a nm.
this is starting to sound a little bit like the "eyespy and mytrycrafts show," if you'll pardon my poor sense of humor. It makes more sense that we see the infrared laser light exactly because the spectrum of the laser is NOT narrow - we see it because part of its spectrum is visible. Our eyes are not sensitive to light that is beyond visible light, isn't that the definition of "beyond visible light"?
Quantum mechanics comes into play I suspect, the spectrum of the laser is continuously changing over time and covers a range of different colors, my guess is from (visible) orange/red to infrared.
I don't think so, i believe that good cables make a difference. I did not buy a silltech interlink for the fun of it or for the name. They just sounded great with my turntable.
The eye is not, unlike a cd player, a digital system. The visible range, from 400 to 780 is where the eye has a reasonable sensitity (and where the sun has the highest brightness, but let's leave that to Darwin). We see green light (around 550 nm) the best but sensitivity drops fast if we go the the limits of the sensitivity. That we put a limit at 780 nm is because sensitivity is so low you will not see it under normal circumstances.
A more practicle example: laser pointers working at 635 nm are to the eye much brighter than the older 690 nm with the same power because the eye is much more sensitive there (closer to the peak 550 nm region). A 1 mW 635 nm laser diode is very bright (and dangerous if you continue looking at it, while a 1 mW 780 nm laser is barely visible. The eye is a very good optical detector to beat (in sensitivity and dynamic range) so even something outside the normal range can be detected, although very weak.
Why don't you take a look at the spectrum of a laser diode in a manufactur's catalogue (e.g Hitachi or NEC). They also include the effect of things like current and temperature on the wavelength, which are small effects in the nm range.
A nice book about optics and lasers, which include the sensitivity of the eye (at day and at night, yes that is different) might be
interesting too.
Well, what is the diffenence between saying that "the eye is more sensitive to 635 nm than 690 nm" and saying that "there is more of the light in the visible portion of the spectrum?" If it is true that lasers are not single frequency devices, that their spectrum extends over some bandwidth, then obviously some of the power of the 690 nm laser is being lost on the invisible portion of the spectrum - infrared - making the light we can see fainter. This explanation makes just as much sense as yours that is saying the eye is more sensitive closer to the green. The point I was trying to make before was that if it is true that the laser spectrum is not single frequency (narrowband), then it starts to make sense that things like green or black or violet coloring of the edges or surfaces of the CD change the sound.
geoffkait wrote:Quantum mechanics comes into play I suspect, the spectrum of the laser is continuously changing over time and covers a range of different colors, my guess is from (visible) orange/red to infrared.
Instead of doing nothing other than come up with half-baked theories, why don't you spend some of your time educating yourself on the issue?
se
Steve, Your theories/statements do not impress me either, I can only wonder how can someone seem so right yet be so wrong, good luck.
geoffkait wrote:Steve, Your theories/statements do not impress me either, I can only wonder how can someone seem so right yet be so wrong
Wrong about what exactly? My statements are no less open to challenge/criticism than anyone else's and I'm always fully prepared to be wrong. So let's hear your argument(s).
Or is this just one of those "Well you're wrong. So there. Nyah!" deals?
se
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