Ive had good results using CDs for brainwave entrainment. When I purchased an iPod Touch (4th gen), the first app I purchased was this AmbiScience app. In general, there are two parts to most of the brainwave apps. First is brainwave entrainment using either isochronic tones or binaural beats. Some apps only offer one or the other. AmbiScience offers both kinds. Second is the choice of many outstanding background ambient music layers. Having complementary ambient music is not completely necessary, but sometimes helps achieving the desired brainwave effect. When it comes to all the AmbiScience apps, the choice and quality of ambient music is really excellent. If you were just looking for ambient music, these apps would be sufficient.
Finally, AmbiScience offers two kinds of brainswave apps. This app (100 beats and tones) simply has EVERYTHING. There is a huge choice of brainwave entrainment frequencies and a huge choice of music. There are other AmbiScience that focus on certain kinds of brainwave entrainment, such as sleep or meditation. This app has that and more. As it turns out, I now own 4 AmbiScience apps that overlap to a large degree, but thats the best example of what I think about AmbiScience and their apps.
I think that isochronic tones probably work better than binaural beats; however, binaural beats are more subtle when using ambient music. Second, in this app, if you want to know the specific brainwave frequency that is being targeted, click on "Tap here for detailed instructions" when looking at the specific entrainment effects. Scroll down. Youll see all the effects along with the frequency. Finally, Ive had better results when using the slower brainwave entrainment frequencies to slow down the brain, such as for sleep, meditation, or releasing beta-endorphins. The entrainment associated with waking up and energizing seem to have little effect on me. Your mileage may be different.
Bottom line: If you want the best brainwave app, this is it. If you just want to focus on sleep or meditation, check out the other AmbiScience apps.