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If you only knew the "gestures" I've made at my computer over the last 5 years dealing with this issue . OK, so upon applying this fix to my work VM this morning, I found a new wrinkle. The basic cause & steps to fix are the same, but the starting configuration has a minor difference. This is with a brand new Parallels VM created from scratch with Windows 8.1 a couple weeks ago. I installed LabVIEW 2014 and a couple other applications, but it's basically a "clean" VM. I'm posting this since I imagine there will be other people stumbling through here over the months/years with brand new VMs – more than those of us with VMs from Parallels 4, to be sure . Anyway, when I went to Control Panel >> Change Input Methods dialog, the only input method installed was the "United States (Apple) - Parallels" one. In order to switch to a different one ("US" in my case), I had to actually Add the "US" layout, then Remove the Parallels one. Interestingly, in this case I did not need to restart Windows afterward. So that's more like Jonas's experience.

I really think you want to use a matched filter. It's basically the cross-correlation that infinitenothing mentioned, and is very standard in radar signal processing to find the time of arrival of an echo even in the presence of noise and clutter. You just need to have a copy of the signal that you originally sent out. It can be implemented as a sliding point-by-point multiply in the time domain or in the frequency domain as a vector multiply (with some FFTs involved). Some googling on Matched Filter should get you there pretty quickly. Gary

Here is a simple snippet that I have used for a similar task before. There are many many ways to process the data, but with signals like what you have I've found that selecting a nominal location for where the 'reflection' should be as well as a window size to search in, you can pretty directly find what you are looking for. The peak may not be what you want, but this is a starting point. You have good SNR so that helps a lot.

See attached image. It should get you off and running. ~,~