The SCV (Speed Controlled Volume) Feature
Automatically controls volume to keep up with top-down background noise
The SCV feature operates by measuring vehicle speed and raising and lowering the volume at selectable intervals. The DCI has 14 “levels” of volume boost so you’re sure to find one that suits your preference. Actually, you get to choose 2 levels and switch between them at any time – just hold the MODE button and tap CH to toggle between the two SCV levels. Most owners use the second SCV level to assign a more aggressive volume setting for Top Down driving. The DCI will remember which setting (high or low) you last used until you change it again. If you want to completely disable the SCV function, just don't connect the vehicle speed sensor wire to the DCI.
As delivered, the DCI is set for levels 4 and 6, which you can swap using the MODE+CH button combo. Level 4 will raise the volume one notch at 15mph, then again after every increase of 19 mph (15, 34, 53, 72mph). Level 6 is a little more aggressive, raising the volume at 15mph intervals (15, 30, 45, 60mph). A simple programming sequence using the dash controls lets you select any 2 of the 14 SCV presets as your "high" and "low" SCV settings.
Note that the DCI is "smart" in how it adjusts the volume in order to prevent too-frequent volume changes. You'll understand better with an example, so let's assume the DCI is set for the default level 6 and you are driving on the Interstate at 60 mph. The volume will have been increased 4 times, at 15, 30, 45, and 60 mph. As you cruise at 60, it would be annoying if every time your speed wavered between 59 and 61 mph the volume lowered and then increased again. So the DCI was designed to wait till your speed slows significantly before lowering the volume. It must see the speed drop by 1/2 of the speed 'interval' before it makes a volume adjustment. In this example, the speed interval is 15 mph, so the volume will not decrease till you slow below 52.5 mph (half of 15 is 7.5). The effect is that if you are cruising at 60 mph, you will need to either speed up to 75 or slow down to 52 before another volume change occurs, which eliminates annoying volume changes if your speed varies by a few mph.