[Skimmertalk] Improving decoder performance and audio quality

Pete Smith n4zr at contesting.com
Tue Sep 23 07:28:47 EDT 2008

Following may be of some interest - I recently posted it on the dxatlas 
Yahoo group, in response to a complaint about a crackling noise in the 
audio output from CW Skimmer:

A couple of things you can try.  Experiment with both drivers for the sound 
card - I found MME to be quieter.  Also, try resetting the priority of the 
CW Skimmer processes in Task Manager to "high" (not real time, it'll 
crash).  If that helps, use a free utility called PRIO to reset its 
priority permanently.  With a dual-core machine, which I don't have, I'm 
told you can also set things up so that Skimmer runs alone on one virtual 
CPU, with everything else on the other.

I think that what is happening is that each of the clicks represents an 
interruption in the data flow to Skimmer, caused by interference with other 
programs running on the same PC.  If you look really hard at the waterfall, 
you'll see these as faint dark vertical lines running from the top to the 
bottom of the screen.  If you can catch one running across a CW signal, you 
will see either a shortening of the code element (if the drop-out occurs at 
the beginning or end) or as breaking into two (an N becomes an S, for 
example).  If you're really quick, you can correlate between the waterfall 
effects and errors made by the decoder, typically reflecting the same 
pattern (N becoming S, in the example above, or A becoming T).

In my setup, using an SDR-IQ, no sound card, and a 2.66 GHz Celeron with 
2GB of memory, I spent many hours stopping all background processes and 
then restarting them one by one (using MSCONFIG).  Stopping them all 
definitely cleaned up the noise (only Skimmer running), but I was never 
able conclusively to figure out which of them could be run without it 
recurring.  Ultimately, fixing the priority at High helped more than anything.

73, Pete N4ZR

73, Pete N4ZR

More information about the Skimmertalk mailing list