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Old 16th February 2008, 03:55 PM   #1
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Default Idea for anti jitter filter



For example in my non os DAC the jitter critical signal is LE, which is 44,1 kHz.

If the signal would not be a square but a sine, there would be sidebands and / or noise visible with a good spectrum analyzer, caused by the jitter.

If that sine runs through a narrow bandpass filter that is tuned to the fundamental, ideally a crystal filter, the sidebands and the noise will be strongly attenuated.

Same will apply to a square wave that will additionally be converted to a sine, but could be shaped back to a square by a comparator.

All IMHO.
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Old 16th February 2008, 11:23 PM   #2
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Filter would have to be extremely narrow since the sidebands are very close of the fundamental. And the stability of such an analog filter would be a problem...
Digital solutions are better (as a FIFO memory). Or DAC's immune to jitter.
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Old 17th February 2008, 01:09 AM   #3
Pulse-R is offline Pulse-R  Australia
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all this assumes that the discs are pressed without jitter - I know the normal pressing technique for most commercial discs has a lot of variance in the pit size. This is one of the problems they try to overcome with XRCD and other similar methods - to eliminate the jitter at the mastering and manufacturing stage. No point trying to eliminate jitter in the playback if it is already there in the production.

my opinion, or course.
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Old 17th February 2008, 07:03 AM   #4
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Default Re: Idea for anti jitter filter

Quote:
Originally posted by Bernhard


For example in my non os DAC the jitter critical signal is LE, which is 44,1 kHz.

If the signal would not be a square but a sine, there would be sidebands and / or noise visible with a good spectrum analyzer, caused by the jitter.

If that sine runs through a narrow bandpass filter that is tuned to the fundamental, ideally a crystal filter, the sidebands and the noise will be strongly attenuated.

Same will apply to a square wave that will additionally be converted to a sine, but could be shaped back to a square by a comparator.

All IMHO.
Hi,

I don't understand why you need to go to a sine first and back to a square if you want to do the filtering?

Jan Didden
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Old 17th February 2008, 09:56 AM   #5
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Default Re: Idea for anti jitter filter

Quote:
Originally posted by Bernhard


For example in my non os DAC the jitter critical signal is LE, which is 44,1 kHz.

If the signal would not be a square but a sine, there would be sidebands and / or noise visible with a good spectrum analyzer, caused by the jitter.

If that sine runs through a narrow bandpass filter that is tuned to the fundamental, ideally a crystal filter, the sidebands and the noise will be strongly attenuated.

Same will apply to a square wave that will additionally be converted to a sine, but could be shaped back to a square by a comparator.

All IMHO.
You don't understand what jitter is. A pure sine wave has no side bands.
If you have a low jitter master clock in your player the jitter of LE will be low enough in NON-OS. Jitter is just timing errors but these are far less critical in NON-OS compared to 8x over-sampling.
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Old 17th February 2008, 09:59 AM   #6
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Quote:
Originally posted by Pulse-R
all this assumes that the discs are pressed without jitter - I know the normal pressing technique for most commercial discs has a lot of variance in the pit size. This is one of the problems they try to overcome with XRCD and other similar methods - to eliminate the jitter at the mastering and manufacturing stage. No point trying to eliminate jitter in the playback if it is already there in the production.

my opinion, or course.

All bits from a CD are stored in a DRAM and read out by the masterclock of the player.
At worst the pit-jitter is a secondary effect.
The kind of DAC, IV-converter and analog stage and filtering also play an important role in sound quality.
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Old 17th February 2008, 10:38 AM   #7
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Default Re: Re: Idea for anti jitter filter

Quote:
Originally posted by QSerraTico_Tico

You don't understand what jitter is. A pure sine wave has no side bands.
If you have a low jitter master clock in your player the jitter of LE will be low enough in NON-OS. Jitter is just timing errors but these are far less critical in NON-OS compared to 8x over-sampling.
A tip: never say that people don't understand things because you don't understand their post

I know a pure sine has no jitter. But you go from square to sine, that sine still has the jitter of the square. That is what you say in your post. Then you go filter the sine to get rid of the jitter sidebands. Then you go back to a square, and that will again introduce jitter. That's working backwards.

If you filter the sidebands from the square, you don't need the final conversion from sine back to square. Less jitter.

Jan Didden
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Old 17th February 2008, 10:42 AM   #8
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Every digital input has a comparator range and some input noise. One has to make sure that the transition between the 0 logical input voltage and the 1 logical level input voltage should be very fast. This can be provided with a fast rise-time digital signal (LE). In this case the jitter caused by the transition will be low. The LE signal should also have low jitter. If you have a low-jitter master clock, the LE coming from the previous stage (error corrector or digital filter) can be synchronized to it. I use the following method:
The LE goes on the input of a 74HCT74. The low-jitter master clock (4.2366 MHz in my case, but can be any frequency that is integer multiple of 44.1 kHz) goes to the Clock input. The Q output goes to the DAC. Something like this:

http://tube.fw.hu/no_oversampling.pdf
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Old 17th February 2008, 11:18 AM   #9
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Lots of confusion. I am talking of a DAC using CS84XX.

If you remove the harmonics from a square, all that is left is a sine.
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Old 17th February 2008, 11:35 AM   #10
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Unfortunately this approach is nonsense. You can't bootstrap a low jitter clock out of a high jitter clock.

Recall the laws of thermodynamics.

You can't win.

You can't break even.

You can't get out of the game.

w
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