Mecheng3;
I haven't seen any testing done with anything other than the Mamba Black and Easylase USB combination. (Well, and the Pangolin setup of course.) However, I can't see how a change is software is going to solve a hardware problem. The DAC should be able to output points at consistent intervals regardless of the software. (The key is that on a USB DAC the timing signal that controls the point output speed is generated locally on the DAC and not slaved to the computer's clock like it would be with a parallel port DAC.)
To test the EasyLase DAC, we loaded up the ILDA test pattern and hooked up an oscilloscope to the X output of the DAC. On the scope you could clearly see the wave shifting from side to side. It was especially easy to see when we zoomed in on the large square wave that is just past the middle part of the pattern. The trailing edge (vertical section) of that square wave would move from side to side on the 'scope. This would manifest in the test pattern as a blurring or slight trembling of the pattern from side to side.
When we hooked up the Pangolin board, the problem went away. (Still using the same scanners and amps.)
Damn - I wish I had thought to take a picture of the 'scope when we were doing all this... ops: Would have made it a lot easier to explain. (D'oh!) I'll try to remember that in the future. (sorry...)
It would have been nice to be able to test other DACs (notably, the JMlaser USB DAC that Jimbo was asking about), but we didn't have one at FLEM to play with. Also, no one at FLEM was running the LDS software, though honestly I don't think it would have made any difference. (see above)
Don't get me wrong; the effect was subtle and only really manifested itself when we looked closely at certain portions of the test pattern. When displaying shows, you would probably never recognize that there was a problem. But when looking at the static test pattern, you could tell that something was wrong.
Bill immediately identified it for what it was (sample jitter), but he had to hook up my oscilloscope before the rest of us fully understood his explanation. (Well, I think some of the more experienced guys (Dzurcher, Clandestiny, etc) also had it figured out right from the begining, but I know that *I* didn't truely understand what was going on until I saw the output on my 'scope.) It was about then that Fred has his "I feel like taking a hammer to my DAC now" moment...
Adam