Brain wave entrainment is a real phenomenon and is useful as one method of investigating how the brain works. But there is no evidence, nor any theoretical basis, for any long lasting effect on brain function or that there is any benefit of any kind. Despite this, there is a huge industry of devices that claim to train your brain waves and have a beneficial effect. I wouldn’t waste a dime on any such device.
Brainwave entrainment is used by millions of adults across the world with no negative effects. However, as with any treatment or therapy, individuals who are prone to seizures should avoid these tones. It is also not advised for pregnant women or very young children whose brain is still developing. If you are concerned about health impacts, discuss it with your health practitioner before you start using our brainwave entrainment products. It is also very important that you use the products in accordance with our instructions.
For many of us, relaxation means zoning out in front of the TV at the end of a stressful day. But this does little to reduce the damaging effects of stress. To effectively combat stress, we need to activate the body’s natural relaxation response. You can do this by practicing relaxation techniques such as deep breathing, meditation, rhythmic exercise, and yoga. Fitting these activities into your life can help reduce everyday stress, boost your energy and mood, and improve your mental and physical health.
There’s an aesthetic element to the music and there are a lot of drone-based sounds and time-stretched sounds, deep, rich bass sounds—there’s a spectrum of sounds within there—and what’s more, there’s a load of 3D processing that goes on to ensure that the mind doesn’t become habituated to them. There’s also a constant, subtle sense, a slow and gradual sense, of the sounds shifting around. And, there are layers of binaural beats.
When you play two separate frequencies in each ear, say 140 Hz and 149 Hz, the difference in frequency is 9 Hz. Your brain compensates for this difference and a third tone of 9 Hz is experienced. This will result in your brain being lowered or raised and tuned into the desired frequency. This is how binaural beats are produced. Headphones are essential for this to work.  
In one study, researchers had a group of participants relax alone in a quiet, low-light environment following an exercise session. They split the group in two — one spent 20 minutes listening to theta-frequency binaural beats while the other listened to a carrier tone and monitored their parasympathetic (rest and relaxation) and sympathetic (fight or flight) nervous system activity. Researchers found the group that listened to binaural beats experienced an increase in parasympathetic activity and a decrease in sympathetic activity, along with higher rates of self-reported relaxation.

Research shows that binaural beats can literally drive brain activity into specific brain states (Gamma, Beta, Alpha, Theta or Delta). Without any effort and naturally, you would have your brain activity to synchronize with the binaural beat; it will become organized and coherent, and eventually, the left and right hemispheres of your brain will start to be balanced creating a very unique state called “hemispheric synchronization” (equal frequency and amplitude of the wave forms in both hemispheres). This extraordinary brain state is very powerful and normally unattainable without this kind of stimulation. Through the entrainment of brain waves, binaural beats can influence the brain in a very subtle way, inducing states of relaxation, sleep, meditation, creativity…

Binaural beats, or binaural tones, are auditory processing artifacts (apparent sounds) resulting from the stimulation of the ears with two different sound frequencies. In fact, when two different vibrations are delivered to the brain separately through each ear, using stereo headphones, the two hemispheres of the brain function together to “hear” and perceive not the external sound signals, but a third phantom signal. This resulting signal, discovered in 1839 by Heinrich Wilhelm Dove, is called “binaural beat”. The effect on the brain waves depends on the difference of each tone. For example, if a sound frequency of 300 Hz is played in the left ear and 307 Hz in the right one, then the binaural beat would have a frequency of 7 Hz (“frequency following response”) which corresponds to the Alpha brain state, generally associated with relaxation, visualization and creativity. The beating tone is perceived as if the two tones mixed naturally, out of the brain. For the binaural beat effect to occur, the difference between the two frequencies must be small (less than or equal to 30 Hz), otherwise, the two tones will be heard separately, and no beat will be perceived.
“The great neuroscientist W. Gray Walter carried out a series of experiments in the late forties and fifties in which he used an electronic stroboscopic device in combination with EEG equipment to send rhythmic light flashes into the eyes of the subjects at frequencies ranging from ten to twenty five flashes per second. He was startled to find that the flickering seemed to alter the brain-wave activity of the whole cortex instead of just the areas associated with vision. Wrote Walter, “The rhythmic series of flashes appear to be breaking down some of the physiologic barriers between different regions of the brain. This means the stimulus of flicker received by the visual projection area of the cortex was breaking bounds— its ripples were overflowing into other areas.”

They came to the table with the idea that the entrainment track would “cause” them to be in meditation, which it doesn’t. Or they thought that having the specific brainwaves the entrainment program promotes would “cause” them to be in meditation. It doesn’t. If you really understand the principles above, you’ll understand why. If you don’t grasp why yet, read these principles again and consider what they really mean. The answer is there.
But the notion of changing brain waves is a very appealing one, from a marketing stand point. People can visualize brain waves and we like synchrony. Also, in the computer age, we understand the notion of “programming.” We also have been prepped for the future by movies such as The Matrix, where people could master Kung Fu in minutes by simply “downloading” the knowledge. This gives the whole notion a superficial plausibility. But the science just isn’t there.
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.
While originally brainwave entrainment was achieved by using pure tones of sound, it is now possible to take these tones and blend them with music, rhythms, and natural sounds, such as the sounds of flowing water, bird sounds, or waves lapping on a beach, creating extended tracts of varied and intriguing brainwave entrainment music for everyday use.
♥ I've beeen training in self-hypnosis for a while (under supervision and for a reason) and found that the 8-4 Hz beats put me very quickly in a deeply relaxed state. Definitely the thing! With the timer, I can shut them for the real self-hypnosis. I haven't tried the other beat generators yet, but this one works much better than I expected and clearly does the job. In a few words: I'm impressed!

Meanwhile, the therapeutic benefits of listening to sound and music is a well-established principle upon which the practice of receptive music therapy is founded. The term 'receptive music therapy' denotes a process by which patients or participants listen to music with specific intent to therapeutically benefit; and is a term used by therapists to distinguish it from 'active music therapy' by which patients or participants engage in producing vocal or instrumental music.[37] Receptive music therapy is an effective adjunctive intervention suitable for treating a range of physical and mental conditions.[38]