1. well i wouldnt make such a distinction between normal and not normal, in the context of your brainwave state. normally, you will be in contact with objects and situations which can indeed influence your brainwave pattern in a specific way... for instance, watching a tv program, driving in a car for an hour at a constant speed, sitting in front of a computer screen all day, etc.
so something which tends to shift your brainwave patterns in a specific way should not necessarily be considered artificial or differentiated from what you consider normal experience.
although with brainwave entrainment the effects are very specific and can be strong so you do have to be careful and not overrrun.
personally, i have never experienced anything like the phenomenon you are describing, although i used to have trouble sleeping at night if i listened to beta frequencies too shortly before bed.
2. it would have to be a pretty bad reproduction to change the frequencies by more than a negligible amount.
[This message has been edited by garics (edited April 11, 2005).]