One of the most fascinating and beneficial things about Delta brainwaves is their ability to stimulate the release of anti-aging hormones in the body, such as HGH (human growth hormone). Increased melatonin levels are also common in this state, and regular visits to Delta have also been shown to decrease cortisol levels. (Cortisol is a hormone that is released during stressful situations, that has been linked with the aging process.) In a nutshell, Delta brainwaves are very healthy, and until now have only been accessible to us during deep sleep.
Basically, one frequency of sound plays through one speaker/headphone and a different sound frequency plays in the other speaker/headphone. With these two different frequencies playing in each ear separately, but at the same time, your brain automatically tries to make up the difference in this frequency range and therefore is gently brought into a new, desired brainwave state as described above. An example of this effect would be a 100Hz frequency playing in your left ear and a 105Hz frequency playing in your right ear. Your brain, over several minutes, distinguishes the slight difference in frequencies and automatically adjusts its brainwave state to match this difference – being 5Hz in this example and therefore putting your brainwave into a Theta state. Pretty cool huh?!
[…] We are fortunate in this day and age to have technology available to us that effortlessly leads the brain into deep meditation, through a scientific process called the ”frequency following response”.  This amazing technology, most commonly called brainwave entrainment, substantially enhances the meditative process, and allows people in their very first session to reach brainwave states that would otherwise take several years to reach through traditional meditation techniques.  This means that you can start reaping the powerful benefits of meditation quickly, and without having to exercise your “discipline muscle” at all!  If you are interested- learn more about brainwave entrainment. […]

Hi Marko, that isn’t one of my videos you referred to, so I can’t really answer you properly as I don’t know how their track was created. For the best answer, you should really contact the video creator. There isn’t any research that I’ve seen to suggest that you could harm your health by looping a delta track. During a typical sleep cycle, your brainwave activity will usually go up and down between the delta and theta range. It may be that you won’t experience the same quality of sleep if you spend most of your time producing mainly delta activity. With my 8-hour sleep track, I fluctuate the frequency range to try and emulate a typical sleep cycle
I wouldn’t personally recommend listening to delta wave frequencies for depression, so I’m not sure who advised you to do that? People with depression usually have a higher ratio of theta and delta wave activity, so I would normally recommend listening to high alpha wave and low beta wave frequencies, to help balance things. I have some 10Hz alpha tracks for serotonin release, which you can try for free on my YouTube channel here: I also recommend you give these SMR (low beta wave) tracks a try: I hope that helps.
Subsequently, the term 'entrainment' has been used to describe a shared tendency of many physical and biological systems to synchronize their periodicity and rhythm through interaction. This tendency has been identified as specifically pertinent to the study of sound and music generally, and acoustic rhythms specifically. The most ubiquitous and familiar examples of neuromotor entrainment to acoustic stimuli is observable in spontaneous foot or finger tapping to the rhythmic beat of a song.