Digital Audio Jitter explained in simple terms

DonH50

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Jun 23, 2010
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In general S/PDIF is likely to have less jitter but an asynchronous DAC will greatly reduce the impact of jitter. S/PDIF connections are often less noisy than USB connections, but for the case of a PC in particular I would not expect that to be true since ground noise injected into the signal is probably similar for either source from a sound card.

My guess is you are unlikely to hear jitter with any decent DAC.
 

Vincent Kars

WBF Technical Expert: Computer Audio
Jul 1, 2010
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By design SPDIF is a clock driven protocol.
Its jitter performance depends very much on the quality of the clock inside PC.

A couple of years ago the recipe was to get a top quality sound card (Lynx, RME) and use the SPDIF out to drive a DAC.

Today an asynchronous USB DAC is recommended.
As it is asynchronous, the quality of the clocking is a property of the DAC, not one of the sender.

A bit more about USB audio: http://www.thewelltemperedcomputer.com/HW/USB_Audio.htm
 

rbbert

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Dec 12, 2010
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There are also a number of asynchronous USB to S/PDIF convertors available. Some listeners have preferred some of them to a direct USB to DAC connection, even with an "asynchronous" DAC USB input.
 

jkeny

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Feb 10, 2012
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There are also a number of asynchronous USB to S/PDIF convertors available. Some listeners have preferred some of them to a direct USB to DAC connection, even with an "asynchronous" DAC USB input.
Yes, even with asynchronous USB, different cables, different playback software can make a difference to the sound. There are two possible reasons I can see accounting for this:
- jitter differences
- difference in CM noise travelling down the USB cable
 

amirm

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There are also a number of asynchronous USB to S/PDIF convertors available. Some listeners have preferred some of them to a direct USB to DAC connection, even with an "asynchronous" DAC USB input.
Yeh, the school of thought there is that you keep the noisy digital circuits in one box and hence separate from the DAC. Same argument is made for having wifi/networking in the DAC. Ditto for video.
 

jkeny

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Yeh, the school of thought there is that you keep the noisy digital circuits in one box and hence separate from the DAC.
I'm not so sure that this line of thought is correct. If you have a separate USB to SPDIF converter you are sending SPDIF signal to a SPDIF receiver with PLL & possibly upsampling. All noisy digital circuits too. Unless you mean that USB digital receivers are somehow more noisy than SPDIF receivers?
Same argument is made for having wifi/networking in the DAC. Ditto for video.
I would totally disagree with this approach - wifi/networking seem to require noisy digital circuits & should be kept far away from the same PS that DAC chip is on!
 

amirm

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I'm not so sure that this line of thought is correct. If you have a separate USB to SPDIF converter you are sending SPDIF signal to a SPDIF receiver with PLL & possibly upsampling. All noisy digital circuits too. Unless you mean that USB digital receivers are somehow more noisy than SPDIF receivers?
I would totally disagree with this approach - wifi/networking seem to require noisy digital circuits & should be kept far away from the same PS that DAC chip is on!
You read my post exactly opposite of how I wrote it!
 

jkeny

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OK, but then I'm confused.
Rbert made the point (I thought :)) that some people prefer a separate asynch USB to SPDIF converter feeding SPDIF to a DAC rather than the DAC's own USB asynch connection.

So I'm not sure what your point was - I thought you were saying that by removing the USB to a separate box it was keeping noisy digital away from the DAC box? My point was that noisy digital is still in the DAC box with SPDIF receivers, PLLs, etc. so I didn't agree with the school of thought that this was the reason for the improvement in sound with some external USB to SPDIF converters!
 

amirm

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You said this: "I would totally disagree with this approach - wifi/networking seem to require noisy digital circuits & should be kept far away from the same PS that DAC chip is on!"

Do you mean they should be in the same or separate box?
 

jkeny

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You said this: "I would totally disagree with this approach - wifi/networking seem to require noisy digital circuits & should be kept far away from the same PS that DAC chip is on!"

Do you mean they should be in the same or separate box?

Separate box!
 

Phelonious Ponk

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Jul 1, 2010
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Ah yes. Jitter in simple terms. Six months and 4 pages later. ;)

Tim
 

jkeny

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See, that is what I said! :)
So, I was correct in my first post - that's exactly what I thought you said & you are confirming it here. I don't know how you replied to my post as "You read my post exactly opposite of how I wrote it! "

Yes, separate box for wifi/network receivers SEEMS to be important but I have no direct experience except turning off wifi in a squeezebox duet which helped the sound but in the case of USB I believe that this "school of thought" is wrong. It might sound like self promotion but I have a DAC with DAC chip & USB receiver in the same, very tight, box which has been reviewed by Bruce B & not found lacking. I have tested separating this into two boxes & there is no improvement, in fact the signal having to be converted from I2S into SPDIF, transmitted & converted back from SPDIF to I2S does not help the sound!
 

jkeny

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Ah yes. Jitter in simple terms. Six months and 4 pages later. ;)

Tim
Tim, remember SNR :) - I'm sure you have something more substantive to say other than this?
 

Johnny Vinyl

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Tim, remember SNR :) - I'm sure you have something more substantive to say other than this?

You've got to admit...it was pretty funny!;)
 

jkeny

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amirm

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Ah yes. Jitter in simple terms. Six months and 4 pages later. ;)

Tim
All things are relative Tim. This is the kind of explanation usuaually given



:)
 

Phelonious Ponk

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Tim, remember SNR :) - I'm sure you have something more substantive to say other than this?

No. Just inserting a little well-needed humor in this oh-so serious discussion of that bit of dust on the edge of the corner of the baseboard behind the chair. :)

Tim
 

jkeny

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No. Just inserting a little well-needed humor in this oh-so serious discussion of that bit of dust on the edge of the corner of the baseboard behind the chair. :)

Tim
Ah, you should have left it at your last post - now you are adding nothing but cynicism, instead of humour, pity!
 

Johnny Vinyl

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May 16, 2010
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Ah, you should have left it at your last post - now you are adding nothing but cynicism, instead of humour, pity!

Perhaps not funny, but true!:)

And Tim..I know you can do better than that!;):)
 

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