Using slapback delay on rap vocals is very commonly overlooked, but to me, it is an essential effect that I will use on every vocal I mix. Check out this record where I use slapback delay to create a sense of texture and depth in the vocal.
Remember, this is an effect that is nearly impossible to hear. It is more so something that you feel, rather than hear.
Gear Used: Sony a6300 - http://amzn.to/2shey1b Sony 10-18mm - http://amzn.to/2sx3iBV Joby GorillaPod - http://amzn.to/2sCBIhO Rode VideoMic - http://amzn.to/2sCEgMS