filter and noise
I think he’s asking about adjusting the averaging time for the speed. Instantaneous GPS speed readings will sometimes jump around a bit because of the random variability from one position to the next (the noise he’s referring to). I believe GPS units eliminate this by calculating speed by not just comparing where you are this second to where you were last second to get speed. Instead, they compare your average position over the last couple seconds to your average position over the next couple seconds. The result is a much more accurate speed reading that doesn’t erratically jump from 10 knots to 1 knot.
I have seen some bigger fixed-mount GPS units that allow you to adjust how much averaging they do, but I haven’t tried to do it on handhelds, so they may offer the same option, or maybe not. Don’t know. Of the various Garmin GPS units I’ve used, I’ve always found the default settings for speed to be sufficiently dampened, but also sensitive enough to tell in a second or two if tweaking that sail, or increasing your cadence had an effect on speed.