Are you referring to Binaural Beats? I gave some a try when I first started LD’ing and didn’t have much success. However, some people find them very helpful; it seems to be one of those “your mileage may vary” LD aids. There is a big topic about it here, although it is somewhat old, and there is a Brainwave Generator Tutorial in the Tutorials section as well. There are some other posts if you search around.
Hopefully someone more knowledgeable can come along and post a better answer 
.