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Old 7th January 2013, 04:35 PM   #1
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Default Why worry about the digital source?

Hello,
in the last months I've been reading a lot about digital sources and related issues, I've also been arguing with some enthusiasts of the CMP2 system.

I'm not an expert, so I could have misunderstood something, but here is what I think about how a D/A converter should work:
(1) store the input data in a buffer
(2) generate a clock signal
(3) make a conversion of the stored data using the internally generated clock

If things were as simple as that, as long as the digital source provides a bit-perfect digital stream, any other variable (i.e. the jitter of the stream) should be irrelevant.

Instead, we're reading a lot of threads about:
- differences between digital buses and interfaces (USB vs. Firewire vs. S/PDIF coax vs. S/PDIF optical)
- differences on the source hardware (with a lot of computer optimization efforts)
- differences on the source software (when it is a computer)

So, how can all this make sense?

If there's the tecnology to obtain a result which is not dependent on the digital source, why aren't enthusiasts going after it, spending time on a lot of optimizations of their computers, instead?

What's the problem with the currently available technologies?

Thank you to anyone will help me answer this question
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Old 7th January 2013, 04:57 PM   #2
Julf is offline Julf  Europe
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Quote:
Originally Posted by Interference View Post
(1) store the input data in a buffer
(2) generate a clock signal
(3) make a conversion of the stored data using the internally generated clock
One small missing piece is the synchronisation between your input data buffer and wherever your data is coming from. If you have asynch USB or feed the source with your DAC clock, you are OK, otherwise you have to do something about the end-to-end synchronisation issue.

If your buffer is small, you will eventually either fill up the buffer or have an empty buffer, as the clock of your source will run slightly slow or fast compared to your DAC. If you have a large buffer, you will have significant delay/latency - a nuisance with pure, recorded audio, but a real problem with simultaneous video or a live situation.
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Old 7th January 2013, 05:00 PM   #3
Julf is offline Julf  Europe
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Quote:
Originally Posted by Interference View Post
If there's the tecnology to obtain a result which is not dependent on the digital source, why aren't enthusiasts going after it, spending time on a lot of optimizations of their computers, instead?
Lack of knowledge/information/understanding combined with audiophile folklore and superstition?
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Old 7th January 2013, 05:02 PM   #4
qusp is offline qusp  Australia
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besides, there is =)
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Old 8th January 2013, 02:33 AM   #5
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Quote:
Originally Posted by Interference View Post
If things were as simple as that, as long as the digital source provides a bit-perfect digital stream, any other variable (i.e. the jitter of the stream) should be irrelevant.
Bear in mind that a digital source doesn't exist in total isolation. Well actually maybe a few do - a battery powered SD-card player springs to mind. This is the closest you're likely to get to a 'perfect' digital source.

Quote:
Instead, we're reading a lot of threads about:
- differences between digital buses and interfaces (USB vs. Firewire vs. S/PDIF coax vs. S/PDIF optical)
- differences on the source hardware (with a lot of computer optimization efforts)
- differences on the source software (when it is a computer)

So, how can all this make sense?
Its not just bits which come across the digital interface, its also noise. Called 'common-mode noise' this is an elephant in the room for digital systems. A large proportion of what are popularly called jitter issues are related to this.

Quote:
If there's the tecnology to obtain a result which is not dependent on the digital source, why aren't enthusiasts going after it, spending time on a lot of optimizations of their computers, instead?
I guess the answer to that one is 'convenience' - battery powered SD-players aren't up to the storage level yet of computers, nor do they have the fancy features.

Quote:
What's the problem with the currently available technologies?
Not much wrong IME if you choose the right technologies and implement them with plenty of attention to detail.
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Old 8th January 2013, 03:16 AM   #6
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You may find this post interesting: john westlake products info
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Old 8th January 2013, 03:22 AM   #7
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Yes its very interesting, Mr Westlake is an astute designer. His point no.3 is what I was talking about above.
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Old 8th January 2013, 06:20 AM   #8
Julf is offline Julf  Europe
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Originally Posted by abraxalito View Post
Its not just bits which come across the digital interface, its also noise. Called 'common-mode noise' this is an elephant in the room for digital systems. A large proportion of what are popularly called jitter issues are related to this.
This shouldn't be an issue with optical S/PDIF (TOSLINK), and USB interfaces can be isolated either with magnetics (transformers) or optics.
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Old 8th January 2013, 06:39 AM   #9
marce is online now marce  United Kingdom
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And if a device does interfere with TV reception it is either badly designed or faulty, that an EMC problem, and anyone involved with real world design will know that such gear would fail the EMC tests and should not be sold, but its a nice comment to feed the fear of digiatl systems.
I second Julf comments earlier.
Quote:
Bear in mind that a digital source doesn't exist in total isolation. Well actually maybe a few do - a battery powered SD-card player springs to mind. This is the closest you're likely to get to a 'perfect' digital source.
could you explain this bit of fallacy please, though again it shows the Audiophile view towards digital, non linear PSU's, battery power (not the perfect solution people think, without some regulation and filtering).
The other problem is 'Dark Bits' as discovered by Qusp, luckily these only affect digital systems that have to handle audio. Luckily the rest of the systems in the world that rely on digital to run dont and seem to work quite well, such as the internet, transport systems CERN, banking system BSYKBetc etc.
Put your CD's on a hard drive and you get rid of the real week link, just dont move your data from disk to disk (like I do) you may induce low level digital distortion (and yes its the second time I've brought this up, but as no believer will discuss this phenomana with me, I shall keep digging till they do.
Keep on fretting
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Old 8th January 2013, 06:42 AM   #10
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Quote:
Originally Posted by Julf View Post
This shouldn't be an issue with optical S/PDIF (TOSLINK)
Agreed - its not a matter of 'should' its not an issue. But those links have other issues - being not very wide bandwidth and non-linear bandwidth to boot, jitter does tend to become an issue IME.

Quote:
and USB interfaces can be isolated either with magnetics (transformers) or optics.
They can indeed though not with infinitesmally low capacitance, only at DC.
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