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In Reply to: RE: An insolent provocation .... if a usb dac is very well design (and built) the pc quality should not matter posted by Tony Lauck on December 11, 2014 at 07:52:16
Tony,
Common optical isolator are way too slow for the sample rates I run my stuff at.
Pulse transformers that are off the shelf suffer bandwidth limitations that are not easy to overcome.
The bit at the end is not so difficult... I had that for ages in most of my DAC's.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Follow Ups:
"Common optical isolator are way too slow for the sample rates I run my stuff at."
Here you go. Even a model where you can run the clock in the reverse direction without requiring a separate chip. (Of course this is only a spec sheet, may be useless marketing BS.)
Yes, you will have to reclock it.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Tony,
I am familiar with NVE's isolators (and most other from any major manufacturer). Please enquire into the operating principle, then you might see why having these can be worse than having no isolation.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Most XMOS designs only need 24.576MHz across the I2S interface. This is easily isolatable. Why do you need 50MHz?
Hi,
> Most XMOS designs only need 24.576MHz across the I2S interface.
Well, I need more than that, ok?
> This is easily isolatable.
Depends on your definition of "easy" and "isolate".
> Why do you need 50MHz?
Now that would be telling, no?
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Look, I also use 45 and 49MHz MCLK, but I don't need it in the I2S XMOS interface.
I'm sure some of the crypto circuit designers have a handle on this problem. I never got close to those particular spooks, however. The spooks that I did meet with in person were scary enough.
As you pointed out, there are optical transmitters and receivers that work at multiple gigabit rates. There are probably other suitable design techniques to deal with power/ground noise affecting signal transitions, or somehow decorrelating the noise from the musical signal, thereby rendering it benign. I'm a systems guy, not a circuit designer, so I'm afraid I can't help you out with details.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Hi,
> I'm sure some of the crypto circuit designers have a handle on
> this problem. I never got close to those particular spooks, however.
I suspect they do, from a different angle. But Deep Crypto scares me, the people into in are a bit odd.
> As you pointed out, there are optical transmitters and receivers
> that work at multiple gigabit rates.
But not necessarily ones optimised to carry 50MHz/50MBPS signals with low jitter, or at prices that make inclusion in relatively inexpensive commercial equipment feasible.
> There are probably other suitable design techniques to deal
> with power/ground noise affecting signal transitions, or somehow
> decorrelating the noise from the musical signal, thereby
> rendering it benign.
Yes, but that does not really help with things that can only isolation (or breaking the noise loops in other ways) can fix.
What we (Computer Audio) need are commoditised USB2.0 High Speed isolators OR good isolators for I2S style digital signals up to 100MHz that do not operate based on RFI producing principles and have low jitter.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
The crypto people are very much concerned with jitter on their signals. Jitter provides a "covert" channel that can leak secret information, bypassing the encryption algorithms. I'm sure they work with signals that are vastly faster than 50 Mbps these days. As to how fast they want to go, I was told , "ten times faster than the fastest that is possible".
You may find this article interesting.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Tony,
Interesting, but fails to answer "commoditised solution".
Now I remember precisely why I find Deep Crypto so scary...Thank you not for reminding me.
Actually, I gave up on anything serious crypto in the 90's, switched to everything in the open and use cypher instead. Cypher cannot be broken mechanically, though it can be compromised (e.g. the Midway affair in WWII).
In fact, Crypto did not work well even in WWII, Enigma anyone?
In the presence of near turing capable analytic engines almost no cryptography is uncrackable.
If you ever spend time in China ( I get to go one or two times a year - married a chinese gal), the level of deep package inspection the government there employs is something else. They leave my VPN connections alone as long as I do not do anything "naughty" (meaning I am trying to look up something their censorship system think is, not Porn or the like, not even politics mostly).
But as soon as I do - my VPN connection is choked off.
0kbps. Not cut, mind you, choked off.
Then I have to change the server and reconnect. And get choked off 3 minutes later again.
And I am not using ordinary or free VPN's either (nor am I one of the usual gibronis, I use near mil spec stuff!). Because of the high annoyance factor of this I plugged about any possible leak on my machine and they still get through all the ICE, somewhere...
They must have machines that eat 256 Bit keys for a light snack, at ISP level too, to monitor what is inside my VPN Tunnel. Scary. Expensive.
Back to music.
Deep Crypto is too scary. WAY TO SCARY.
Commoditised Isolation Solutions please.
As in "Fast(ish ~100MBPS), Low Jitter ( < 20pS would be nice), Cheap (say 5 USD for EIAJ Dual Mono)".
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
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