inside voices are in your head
outside voices are coming from any external source. it can be a real person thats really not saying anything or even something like a plant.

voices inside your head can seem more like thoughts can be loud like if you have headphones on. or a speaker inside your head. one sure thing is if you cant control them and they talk about things that you dont say. especially if they are in diff gender than you. stuff like that.

outside voices are more easily explainable. you can hear sounds or music that isnt there. you can hear phrases or a word (or words). or you can being called.

i have voices both inside and outside of my head. i get outside voices speaking a sentence here and there and my name. lots of mumbling and snippets of conversing. inside its like a loud speaker and they have a constant dialogue most of the day. i do have breaks from them though from time to time. they try to get me to tell them stuff and then theyll tell me to do things. loads of different stuff.

im 22 yr old female and the voices are usually 40 to 50 yr old men. i have no idea why.