After 2+ years of using Reaper as my main DAW, I discovered something while recording my track Jihad Ballad.
The guitar tracks both have the built in Reaper EQ. I was sitting here playing with the automation for each track when I noticed that I could automate the EQ itself. I started playing around with the different bands and found a cool effect to use in the track by automating the 4th band (high frequency).
Here's how it's done.
Have your track contain the built in Reaper EQ. Make the 4 band or highest frequency band a Low Pass:
Once this is done you'll have a blue bar show up under your track. Create points on the bar by holding Shift and left click where you want this effect start and again to end.
Now decrease the first point you made so that it's much lower than the second:
You can hear how I used it on Jihad Ballad HERE