I admit, I have never found it to be a 'need' of any kind, but I do appreciate audio that can help get me very relaxed. Although I am a big fan of The Monroe Institute's SAM and older Hemi-Sync stuff, you have to look carefully for things that are just that brainwave audio and not a lot of narration or guided stuff. BrainSync has a lot of just-the-audio stuff. I used their "Deep Meditation" CD quite a bit.
There is a lot of free stuff on youtube. Just search with 'binaural' in your string. And try to avoid the 'sleep' ones because, you know, otherwise you might end up doing ZzzzzzRV.
Mostly if I have a decent amount of time (rare) I prefer things that help induce theta state, but you do have to be pretty well rested to do that without falling asleep, or simply getting so altered-state that you're too stupid to ask yourself obvious questions. (An interviewer is very helpful for altered state work.) Otherwise simply 'relaxing music' is nice.
For a long time I listened to this album by lowercase noises called carry us all away (except the 'garden' song I removed) because it was SO relaxing. (His music is 'volunteer donation' on his website.) Not sure why, but my brain now interprets it as a sleep signal, and that stuff is like Audio Ambien or something, so I can't use it for viewing anymore, but it certainly helps me sleep!
I don't tend to use anything WHILE viewing. Just beforehand. I get audio data and have always felt audio might interfere, same way that a lot of graphics or light issues can interfere for me.
If I'm using (I don't anymore, but used to) a format/methodology that is based on
going through a structure really fast so you don't think about it then I would probably prefer corporate hard rock music first (not during). Because it is energizing while being slightly numbing. It does pretty well at killing some degree of conscious meandering thought. That's why it tends to be nice to listen to very loudly if you're upset about something your brain wants to obsess about. Dangerous to do in the car, though, for speed limit reasons.
PJ