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Doppel, as it stands, delivers two separate rhythms -- one high and one low. The high rhythm essentially delivers a rhythm which is higher than your resting heartbeat, and the lower one which is lower. And it works in a very similar way as to when you listen to upbeat or downbeat music. So, in the same way that upbeat music can excite you or bring you up, make you more alert; doppel does this. And it does the same thing with the downbeat tempo which you feel calming you down and even helping you into sleep.