[axeman]

Hi again,

Had the opportunity to run DPC Latency Checker on the PC and found some very interesting results:

Started with my USB-based WLAN card in, as I needed it to download the application anyway. When I first launched the tool, it seemed to indicate average USB latency of nearly 40 μs, with an initial peak at 746 μs. Let it run for about 5-10 minutes and then caught a big spike up to 4350 μs. Figured it was time to pull the WLAN card out and start fresh.

As I suspected, things got a lot better right away. The average latency was around 10-15 μs, with the maximum captured at 44 μs. Let it run for about 15 minutes and eventually caught a spike all the way up to 88 μs. Based on this set of results, I thought things might actually be OK.

So I figured it might be a good idea to plug in the US-1641 at this point and see how that affected the readings--and this is where things started to disintegrate:

Initially caught some spikes up to 2438 μs (which led the program to prompt that digital audio/video would probably experience dropouts). Let it sit for a while and the spikes actually increased all the way up to 3199 μs. Started REAPER at this point and the maximum latency jumped up a little to 3255 μs right away. After playing a bit of my test recording, however, that raised all the way up to 4495 μs and eventually peaked at 5168 μs. At this point I shut REAPER down, which caused an even bigger spike--up to 7525 μs--but that, in itself, didn't really surprise me, as I figured there might be some bindings to release.

I restarted REAPER and decided to try adjusting the latency setting within the US-1641 driver. Meant to start by increasing the latency to maximum ("highest"), but accidentally went to the other extreme ("lowest")--and all hell broke loose. DPC Latency Checker showed a lot of spikes, with the highest reaching 17421 μs, right before REAPER hung (at which point the US-1641 driver-setting application would not open). Rebooted and set the US-1641 for maximum latency and still saw reasonably bad performance, with averages in the 30 μs range and a significant peak at 2631 μs.

Based on these results, am I correct in assuming that the US-1641 and/or its driver is really the most likely source for these performance problems? Is there any reason to expect that the USB ports/drivers/BIOS on the Dell is still at least a significant part of the problem?

By the way, I attached four of the screen shots to this message, just in case anyone wants to check out the details. Here's a brief legend (in chronological order):

- final_sample_no_WLAN.JPG (taken with WLAN out, before attaching the US-1641)
- 2nd_sample_after_playing_audio.JPG (taken after the US-1641 was inserted and audio played in REAPER)*
- 1st_sample_after_stopping_REAPER.JPG (taken after REAPER was stopped).
- with_lowest_latency setting.JPG (captured right before REAPER crashed, after accidentally setting the US-1641 for lowest latency)

*Uploaded this one last, so it's out of order in the attachment list (but in the proper order of the items as listed above).

Assessments/additional insights extremely welcome.

Take care and thanks again for all the help,


Alan