No offense, but now you are just pulling nonsense out of the air. This is obviously beyond you.
If a CD player was constantly over- and under-running the buffer due to an insufficient buffer size it would sound like hell if it worked at all. The only jitter will be that from the clock, there will be none from the transport. You don't need to understand or believe this for it to remain the fact that it is.
Stay clear of personal remarks, please. A warning.
Yes, any effect of the motor etc. on the clock would have to be indirect (via grounding or PSU etc.). How large this effect is is anyone's guess. There is more to crystal clocks than some people think - see any book/discussion/article on oscillator phase noise or jitter. My guess is that in many CD players the crystal itself is not particularly high quality and this may be a bigger effect than the motor. The audibility of the resultant jitter is yet another matter.
Yes, I understand. You have no data, you're just speculating. It's physically possible, I suppose, but I'm surprised that, as often as it's asserted, there's nothing to back it up.
It's basic logic - you put a device with a widely fluctuating & high current draw (servo motor) on the same power supply as a device with a very sensitive PS requirement (clock) & you say it's speculation!! Please don't use the phrase "competently designed"
EDIT: I didn't say "it does" I said "it can" - please read more carefully, SY
EDIT: I didn't say "it does" I said "it can" - please read more carefully, SY
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Actually, neither link show what you're claiming. In fact, the Dennis, Dunn, and Carson paper states exactly the opposite.
Poor peufeu got buried in spam for his efforts. Nonetheless, he showed that there was lousy shock sensitivity in a cheap and about-to-fail transport. Not exactly profound, but he at least went out and did something.
Poor peufeu got buried in spam for his efforts. Nonetheless, he showed that there was lousy shock sensitivity in a cheap and about-to-fail transport. Not exactly profound, but he at least went out and did something.
No they found amplitude modulation of the analogue outputs by SERVO related interference - I don't care what one wants to call it -it's distortion caused by servo interference - something you seem to think is "physically possible".
Peufeu showed a direct connection between the servo tracking operation (caused by shock or any other mechanism) & jitter of about 2nS on the SPDIF waveform! Trying to use the excuse that it was a substandard device doesn't cut it - it's the old "competently designed" canard yet again.
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Peufeu showed a direct connection between the servo tracking operation (caused by shock or any other mechanism) & jitter of about 2nS on the SPDIF waveform! Trying to use the excuse that it was a substandard device doesn't cut it - it's the old "competently designed" canard yet again.
So you're arguing over the term that's used to describe this connection between the servo motor & the distortion caused by it - pretty weak SY! I'm particularly fond of Wagyu sashimi.
Peufeu said: "Now, when the disc is rotating, we see about 1.5-2 nanoseconds of jitter (yes this is huge)" & showed a scope shot of it. He goes on "In the CD player, there is a spindle motor, another motor to move the lens along as the CD is read, and a tracking servo to align the lens and keep it on-track as the CD rotates. This tracking servo is constructed with moving coils, driven by the electronics in a feedback loop to keep the lens well positioned.
This is inevitable, but it is particularly nasty, as vibrations of the case (caused by music playing) will make the CD and pickup vibrate, and this will have to be compensated by the tracking servo. The player must move its lens to compensate the movement of the disc, which means the currents in the moving coils will vary according to the vibrations.
All these coils and motors create stray electromagnetic fields which are picked up by the CDP electronics. They are probably driven by PWM which causes even more interference."
I like shabu-shabu restaurants!
Peufeu said: "Now, when the disc is rotating, we see about 1.5-2 nanoseconds of jitter (yes this is huge)" & showed a scope shot of it. He goes on "In the CD player, there is a spindle motor, another motor to move the lens along as the CD is read, and a tracking servo to align the lens and keep it on-track as the CD rotates. This tracking servo is constructed with moving coils, driven by the electronics in a feedback loop to keep the lens well positioned.
This is inevitable, but it is particularly nasty, as vibrations of the case (caused by music playing) will make the CD and pickup vibrate, and this will have to be compensated by the tracking servo. The player must move its lens to compensate the movement of the disc, which means the currents in the moving coils will vary according to the vibrations.
All these coils and motors create stray electromagnetic fields which are picked up by the CDP electronics. They are probably driven by PWM which causes even more interference."
I like shabu-shabu restaurants!
Yes, pf makes some assertions. No data to back it up, though.
So the old jitter-from-servo-modulation meme is still audiophile lore. Physically possible, maybe, but at this point, apparently just handwaving. If memory serves, Peter van Willenswaard looked for this effect some years ago and was also unable to find it- but I don't have the reference to hand and I might be mistaken.
I have no idea what the sashimi and shabu-shabu stuff means. I don't eat that stuff anyway. Dead animals. Eccch.
So the old jitter-from-servo-modulation meme is still audiophile lore. Physically possible, maybe, but at this point, apparently just handwaving. If memory serves, Peter van Willenswaard looked for this effect some years ago and was also unable to find it- but I don't have the reference to hand and I might be mistaken.
I have no idea what the sashimi and shabu-shabu stuff means. I don't eat that stuff anyway. Dead animals. Eccch.
It's not so hard to understand.
1. We have a DC motor that needs to rotate with precise rpm's.
2. We build a control loop with refference input from a xtall oscilator via a PLL loop and a VCO. Measured input of the loop is the data frequency from the laser diode. Those two signals go to a phase comparator that, via a Proportional-Integrative module, creates the error control voltage for the DC motor.
3. That voltage controlls the speed of the motor (via driver).
Now, the electrical motor will have tendency to under/overspeed and that will be corrected by the control loop. There is no electro-mechanical device that can spin perfectly constant without an outside control.
A scope on the motor voltage will show that the voltage continously varies (slighty).
That minute rpm variations (+/- centered on the desired rpm), together with lens focusing and tracking will result in minute variation in data rate. Sure, in AVERAGE, the speed and data rate is very accurate - control loop keeps the average at the crystal precision.
But instantaneous speed and resulting data stream will have variations - aka jitter.
How big are those variations depends a lot of the quality of the electrical motor and of the focusing/tracking voice-coil. The mechanical bearings of those have a big importance here, but not only.
If anybody thinks that a better crystal refference can "fix" a bad motor/lens coil... that's too bad.
1. We have a DC motor that needs to rotate with precise rpm's.
2. We build a control loop with refference input from a xtall oscilator via a PLL loop and a VCO. Measured input of the loop is the data frequency from the laser diode. Those two signals go to a phase comparator that, via a Proportional-Integrative module, creates the error control voltage for the DC motor.
3. That voltage controlls the speed of the motor (via driver).
Now, the electrical motor will have tendency to under/overspeed and that will be corrected by the control loop. There is no electro-mechanical device that can spin perfectly constant without an outside control.
A scope on the motor voltage will show that the voltage continously varies (slighty).
That minute rpm variations (+/- centered on the desired rpm), together with lens focusing and tracking will result in minute variation in data rate. Sure, in AVERAGE, the speed and data rate is very accurate - control loop keeps the average at the crystal precision.
But instantaneous speed and resulting data stream will have variations - aka jitter.
How big are those variations depends a lot of the quality of the electrical motor and of the focusing/tracking voice-coil. The mechanical bearings of those have a big importance here, but not only.
If anybody thinks that a better crystal refference can "fix" a bad motor/lens coil... that's too bad.
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Gosh... I just said a few posts above that the buffer holds only 64 samples, so it is good to take care of jitter "faster" than 1380 Hz. The low frequency jitter (the one that receivers and DAC's are vulnerable to) needs BIGGER buffers. And yes, the above motor/coils variations have low frequency due to inertia...
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Here's some buffer info for skip protection in portable players: http://focus.ti.com/lit/an/spra831/spra831.pdf
A non-portable transport wouldn't need that much memory.
Sheldon
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