Do you mean the ringing spect of the "boom"? That's basically a super fast delay effect - similar to comb filtering.
e.g.
Delay ---> Delay time 10ms;
Feedback ---> medium / medium-high (just watch that it doesn't feedback back too much!)
The quickly repeated delayed signal effectively creates a repeated wave of length 10ms (that layers over the sound), which gives a sound a ringing "pitch" effect. Shorter delay times therefore increase (raise) the pitch, and longer decreases / lowers the pitch effect. It can be a very cool effect in moderation / if use well...
Hopefully that helps?