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The mechanism of the chirping sound on a CD player
distill
post Sep 1 2013, 12:31
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What makes the chirping sound on any CD player? I am not talking about any problem or failure but just the normal seek sound a CD player mechanically produces. Why does the pitch modulate so much, it kind of sounds like the tracking is accelerating and deaccelerating, jumping to almost random locations until finally the correct position is found.

Bonus question: are there any CD players that have no chirping sound at all?
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[JAZ]
post Sep 1 2013, 13:19
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I was trying to find some images that could explain it well, but so far I've only found one. Please, see the part "Internal mechanism of a drive" in the wikipedia's Optical disc drive entry. (Click on it to see a bigger image. You can also see at the beginning of the entry, the unit of a laptop)

There are two main parts in the picture: On the lower side, there is the motor that makes the cd spin. This motor takes exactly the place of the center hole of a CD, and either with pressure, or by a moving piece that the drive places above the drive, the CD is kept fixed in this place.

On the upper side, there is the lens (the black rounded thing with a rounded blueish thing on the left), that moves from lower to upper side of that image using the rail (the bar that is on the right side of the image), which is also moved by a motor (on the upper right corner of the image. Its movement moves the dented bar that is connected to it and that ultimately moves the lens).

There is a third thing that moves, but cannot be cleary seen in that image. The lens itself (i.e. the blue thing) moves up and down (vertically, not horizontally) to move it nearer to the disc surface.

(On tray loading units, also this whole piece shown in the image is moved up to press the CD up. On laptop units this is not needed)

So, resuming: cd spin motor, lens positioning motor and lens focus.

The first thing that is done, obviously, is start spinning the CD (ok, first thing might be moving the lens position next to the cd spin motor. Contrary to vinyl, CD's are read from inside to outside part, since the outside part gets damaged easily)


So, the cd spin motor starts to spin the disc. This spinning is what makes the "whoosssh" sound that is more annoying, especially if it spins fast. At CD Audio speed, it is fine.
(Computer units have a habit to spin fast and slow down when getting information, to sped up again when reading actual data.)

Next, the lens positioning begins, It has to seek the CD information (to know what contains this disc, if audio, if data, how many tracks...). This is what makes the "nyic-nyuc, nyiuc..nyic-nyuc". Initial seeking allows to know the exact start of data. (millimetric precision is not enough)

The lens zooming makes a quieter noise, more like "tap, tap, tap" (when it zooms out), and might even be noiseless.. It does not use a motor, but instead is magnetically positioned.


So i guess your question is more around why lens positioning needs so much seeking, and on a related question, if the seeking could be more silent.

I don't know the exact details of how it seeks so I cannot give an exact answer on the first. About the second, there might be solutions, but I doubt there is any incentive nowadays to do so. Concretely, Hard drives used to be very noisy (not only when seeking, but just spinning could be annyoing if you had it on your bedroom and you were to go to sleep). They improved on that regard, but their price continued to be high enough for developing better technologies.
On the other side, cd drives are quite a commodity with no real margin for improvement, and the only way it has to improve is with new disc technologies.
But since blue-ray discs haven't seen the usage of cds and dvds, there isn't much to expect in that field..

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ktf
post Sep 1 2013, 14:36
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QUOTE ([JAZ] @ Sep 1 2013, 14:19) *

Next, the lens positioning begins, It has to seek the CD information (to know what contains this disc, if audio, if data, how many tracks...). This is what makes the "nyic-nyuc, nyiuc..nyic-nyuc". Initial seeking allows to know the exact start of data. (millimetric precision is not enough)

This is usually done with a stepper motor, and these are known to be very noisy. I don't know why, but even industrial versions costing hunderds of /$ make loud sounds when they are used. Hard-disks on the other hand, don't use a stepper motor, that's why they aren't that noisy. As I said I don't know why stepper motors are noisy (I've just never come across a silent one I think) so I don't know whether there are silent ones.

You could use a servo motor instead, but that would be expensive and probably not as fast.


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distill
post Sep 1 2013, 14:45
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That was a nice answer! Indeed, I was just wondering about this because it is such a profound sound of the already dead CD era. So the lens positioning uses a fairly normal motor and that makes the birdlike chirping. The laser itself makes absolutely no sound, I assume.
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ktf
post Sep 1 2013, 15:01
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QUOTE (ktf @ Sep 1 2013, 15:36) *
As I said I don't know why stepper motors are noisy (I've just never come across a silent one I think) so I don't know whether there are silent ones.

There might be a lead about that on wikipedia: http://en.wikipedia.org/wiki/Stepper_motor...rrent_waveforms. It says under microstepping

QUOTE
Regardless of the waveform used, as the microsteps become smaller, motor operation becomes more smooth, thereby greatly reducing resonance in any parts the motor may be connected to, as well as the motor itself.

As this is a more expensive form of driving than the others, the others might induce resonance. It makes sense now I think of it, poles are just turned on and off at very high speed, just like DC motors with a commutator (you know, the very small and noisy ones in cheap RC-stuff), these are switched on and off as well. Properly controlled servo and big (not position controlled) industrial run on nice sinewaves instead, making much less noise.


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