It is a course that covers six months, after each month you move onto the next level of the program. The levels start off with the eye-opening Transcendence and move on to the literally mind expanding levels of Neptune’s Cave and Fusion. With each level you complete, your ability to solve problems and deal with stress goes through the roof, and you will feel a deep sense of emotional bliss.

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: https://www.youtube.com/watch?v=3NSUcuzpRcY&list=PLveg0IEcZWN6T86nhmSrdwG2kMQtcLRou. I also recommend you give these SMR (low beta wave) tracks a try: https://www.youtube.com/watch?v=HGTvBbrEwZQ&list=PLveg0IEcZWN7yaMaKr8F-eWHALk2_zGqY. I hope that helps.
Isochronic tones are the most recent and advanced method for brainwave entrainment audios. With isochronic tones, the same intensity is used for all tones, but they pulsate on and off at different rates. The speed, pattern, and rates of these tones can be changed and altered throughout the recording, and the brain will follow them into desired states. The use of isochronic tones opens up the ability to lead the brain into highly specific states, at specific speeds and intensities. This has opened up the doorway to producing both dominant and subdominant waves(i.e. an alpha brainwave state with subdominant theta waves), and the ability to lead the brain through different waves, at specific speeds (i.e. holding the brain in an alpha state for 10 minutes, then dropping it through theta for 20, and holding it in delta for five before bringing it back into alpha at the end of the recording.) This allows thousands of different possibilities in training the brain, and also makes the process of listening to these types of audios more natural, and more powerful. 
Have you ever found yourself in a tough situation where you couldn’t think of a way out? If you have, it might be due to a lack of Alpha brainwave activity. It’s been proven that increased production of these brainwaves allows people to deal with and solve problems at a faster rate and with far fewer difficulties. This is made possible thanks to the brainwave’s ability to get rid of “mental blocks” that prevent solving the problem at hand.
Another small scale study with 30 children were entrained with a starting frequency of 14 Hz and ramped up to 40 Hz. Following the excitatory-based protocol, they were then given a protocol that started at 40 Hz and decreased to 14 Hz over 6 weeks. The results indicated that the children significantly improved in arithmetic abilities based on the WISC-III.

Transparent Corp's Research Area is arguably the most comprehensive resource for collated brainwave entrainment research.   Update: the main research area on Transparent Corp's website is currently being updated, so it is offline.  However, you can still access their peer-reviewed research paper as a PDF here: “A Comprehensive Review of the Psychological Effects of Brainwave Entrainment“.
“…humans have always been intrigued by the possibilities for influencing mental functioning that emerge from combining rhythmic sound and rhythmic light stimulation. Ancient rituals for entering trance states often involved both rhythmic sounds in the form of drum beats, clapping, or chanting and flickering lights produced by candles, torches, bonfires, or long lines of human bodies passing before the fire and chopping the light into mesmerizing rhythmic flashes. From Greek plays to Western opera, our most popular entertainment forms have made use of combinations of lights and sounds. Some composers, such as the visionary Scriabin, actually created music intended to be experienced in combination with rhythmic light displays.”

For me, brainwave entrainment actually helped me more easily meditate on my own without the technology. There is definitely evidence to suggest that the neural pathways that form from listening to these audios aids the brain in better producing these brainwaves on its own moving forward. Though I used brainwave entrainment for several years, almost daily, there was also a point in my life where I went without the technology and meditated daily on my own. I believe that even this practice was accelerated drastically by my listening to bwe in the past.
Gamma brainwave states are the most rapid in frequency. Gamma has long been considered the brainwave that is able to link and process information from all parts of the brain. It is the frequency that brings with it the ability to process large amounts of information in relatively small amounts of time. Think of generating more Gamma activity as getting a processor upgrade for your brain.

NeuralSync™ is the ONLY technology that utilizes FOUR SEPARATE yet synergistically-interactive frequencies precisely calculated to induce each mental state offered in our catalog. Our exclusive 4-W.T.S.P.™ technology creates waves in a balanced 4-dimensional pyramid that are collectively complementary and interactive. Unlike other related programs that use only a single binaural beat or isochronic tone frequency (or several in sequence), NeuralSync™ applies all four simultaneously to immerse your brain into targeted and harmonizing perspectives.
Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry[citation needed] into whether or not the synchronous electrical activity of cortical neural ensembles might not only alter in response to external acoustic or optical stimuli but also entrain or synchronize their frequency to that of a specific stimulus.[16][17][18][19]
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