USB optical coupling
Jan 13, 2006 at 10:35 PM Thread Starter Post #1 of 10
pburke

pburke

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Anyone ever try one of these to completely isolate their PC from the USB audio device? I'm fighting some gremlins right now with my laptop and while trying to learn about galvanic isolation, this thing popped up in google:

http://www.usb-shop.com/opticis.html


$$$ but it clearly solves the issues once and for all, plus it would make it even easier to run my PC downstairs and the DAC upstairs. Keybard and mouse/screen are already on a cat5 KVM extender.

Here is another gizmo - this time just $250 for a non-optical solution:

http://www.icsdatacom.com/pdfs/USB-GT_ds.pdf

anyone know how these work (transformers, I guess)?

Peter
 
Jan 14, 2006 at 2:29 PM Post #3 of 10
Quote:

Originally Posted by Revliskciuq
A better solution might be to use the Squeezebox over LAN or WIFI, it has digital outputs which you can run into your DAC. You also might want to checkout the Apple Airport Express.



No interest in Squeezebox - I have a DAC that is direct USB-I2S, and I use Foobar for upsampling, etc.

Peter
 
Jan 14, 2006 at 11:39 PM Post #5 of 10
Quote:

Originally Posted by AintLDS
I'd be wary. The conversion of USB-optical-USB will probably impart some jitter or other issues ultimately to the signal.



USB transfer is purely in the computers dream, probably checksumed. Anyway if they are sane, they would not sell product altering the data, since computers are bit-sensitive with possible application error/hang as result of data altering.
 
Jan 15, 2006 at 3:14 PM Post #6 of 10
Quote:

Originally Posted by AintLDS
I'd be wary. The conversion of USB-optical-USB will probably impart some jitter or other issues ultimately to the signal.


it is my understanding that USB is bit-accurate - we're not talking an rF signal like SPDIF here. How else could these things be used to remoe connect server farms to peripherals? Some of these things are sold with 10 kilometer connect capability.

Peter
 
Jan 15, 2006 at 11:15 PM Post #7 of 10
Hmm . . . well now I'm confused. I'm not an engineer so am trying to understand this.

I have the option of outputing data from my USB to my DAC or streaming to my Airport Express and going optical out to my DAC via TOSLink. If they are both bit accurate they should sound identical. But they don't. The USB connection is clearly inferior, not by much, but it's audible. Why is that?

Also, in the Steve Nugent article in Positive Feedback he mentions this:

"Toslink is the worst of the interfaces because the electrical to optical and optical to electrical conversion adds to the jitter. Toslink creates additional stages that the clock must pass through, picking up jitter due to power/ground noise and uncertainty of when the edge (logic change) transitions get detected."

Now, while your USB device is not using Toslink, there are these same conversions going on. Are there timing issues that need to be taken into account when moving data out your laptop to your DAC?
confused.gif


I'm trying to understand this stuff before blowing more money on upgrades so if you guys have a handle on it, please share.
 
Jan 17, 2006 at 10:17 AM Post #8 of 10
Quote:

Originally Posted by AintLDS
Hmm . . . well now I'm confused. I'm not an engineer so am trying to understand this.

I have the option of outputing data from my USB to my DAC or streaming to my Airport Express and going optical out to my DAC via TOSLink. If they are both bit accurate they should sound identical. But they don't. The USB connection is clearly inferior, not by much, but it's audible. Why is that?

Also, in the Steve Nugent article in Positive Feedback he mentions this:

"Toslink is the worst of the interfaces because the electrical to optical and optical to electrical conversion adds to the jitter. Toslink creates additional stages that the clock must pass through, picking up jitter due to power/ground noise and uncertainty of when the edge (logic change) transitions get detected."

Now, while your USB device is not using Toslink, there are these same conversions going on. Are there timing issues that need to be taken into account when moving data out your laptop to your DAC?
confused.gif


I'm trying to understand this stuff before blowing more money on upgrades so if you guys have a handle on it, please share.


1) USB may suffer from ground looping with computer as source of noise.
2) It's done in such way it's error-free (otherwise it would not work with computers) in reasonable time scale. There are two exactly coupled and matched devices with exactly same (huh, not exactly
wink.gif
) clocks. Also, it would not be too difficult to add checksum after each junk of data. Anyway I do not know how exactly it works but it must be bit-perfect since it essentially is a computer device.
 
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