Gamma brainwaves possess the highest frequency we know of. In this state, our brainwaves are so harmonious that many people report feeling elevated states of consciousness, even spiritual experiences. This frequency is often experienced by monks, nuns, yogis, and experienced meditators. Gamma frequencies also enhance memory, awareness, and mental processing.
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.
Delta is the lowest frequency range of .2Hz - 3Hz, corresponding to dreamless sleep, growth hormone release, healing and ultra deep trance. Effective in reducing migraines, chronic pain and blood pressure. By inducing a predominantly Delta state in the brain while remaining awake, you push your brain to operate in a truly unique state that literally forces greater neural adaptation and cross-connection between the regions of your brain.
Recently developed entrainment software has been designed to correct specific imbalances in hemispheric activity associated with undesirable mind-states. For example, people suffering with depression often have more activity in the right hemisphere, and specially designed brainwave music decreases this activity while increasing activity in the left hemisphere, reducing depression.
Some research suggests that the benefits from brainwave entrainment can last a lot longer, and still be seen for some time after you've stopped using it.  Study participants have still maintained improved test scores a few weeks after the stimulation had ceased.  Research on the long-term benefits has so far been minimal though, so how long the effects last is still up for debate.
While a practical understanding of brainwaves has been around for as long as people have been singing, chanting, and drumming, a scientific view of the electrical activity inside the human brain was not published until 1924 when German psychiatrist Hans Berger developed a machine for sensing and recording activity in the brain by attaching small electrical sensors to the scalp of his patients and recording the resulting electrical activity. Berger’s inventions and discoveries were built upon the earlier work of Richard Caton who published animal studies on brainwave oscillations in 1875.
Theta waves have a frequency between 4 and 7.5 hertz, making them slower than more wakeful alpha but faster than the dreamless slumber of delta. Theta brainwaves are the frequencies of nighttime dreams and REM sleep when the brain goes through bursts of activity and eye movement. People also experience theta waves in a state of light sleep, deep relaxation, during meditation and prayer, and when daydreaming. Theta waves produce an experience of inward wakefulness where we become disengaged from the outside world while engaging in inner activity. At the lower frequencies of theta, sleeping states are experienced, and at the higher range of frequency, awake relaxed states are experienced. 

Passively listening to binaural beats may not spontaneously propel you into an altered state of consciousness. One's subjective experience in response to binaural-beat stimulation may also be influenced by a number of mediating factors. For example, the willingness and ability of the listener to relax and focus attention may contribute to binaural-beat effectiveness in inducing state changes. "Ultradian rhythms in the nervous system are characterized by periodic changes in arousal and states of consciousness (Rossi, 1986).
Infra-Low brainwaves (also known as Slow Cortical Potentials), are thought to be the basic cortical rythms that underlie our higher brain functions. Very little is known about infra-low brainwaves. Their slow nature make them difficult to detect and accurately measure, so few studies have been done. They appear to take a major role in brain timing and network function. 
Group exercise or encouraging stressed clients to find a workout partner is an excellent idea because it can provide a support network and accountability. However, there might be clients who find a group setting intimidating or competitive, which could be counterproductive in managing stress. In addition, those who report stress because of work or family obligations might enjoy the solitude of exercising alone. Using a variety of exercises or nontraditional exercises (e.g., exergaming, dance classes, yard work, or rock climbing) is a way to plan activities that are enjoyable to maximize adherence. Knowing your clients’ exercise barriers and stressors will help with planning an exercise program that can address these variables to maximize the benefits for health and stress management.
Meditations that cultivate mindfulness have long been used to reduce stress, anxiety, depression, and other negative emotions. Some of these practices bring you into the present by focusing your attention on a single repetitive action, such as your breathing or a few repeated words. Other forms of mindfulness meditation encourage you to follow and then release internal thoughts or sensations. Mindfulness can also be applied to activities such as walking, exercising, or eating.
That’s why it’s so important to find the proper stress relievers to maintain a strong quality of life. The eight stress relievers above — exercise and yoga, meditation/healing prayer, acupuncture, a nutrient-dense diet, cognitive behavioral therapy, spending more time in nature and being social, keeping a journal and using adaptogen herbs and essential oils — can help you maintain a good mood, remain calm and better handle your day-to-day stress.
You probably already know that sex is a great tension reliever, but have you officially thought of it as a stress-relieving practice? Perhaps you should. The physical benefits of sex are numerous, and most of them work very well toward relieving stress. Sadly, many people have ​less sex when their stress levels are high. Learn how to avoid this trap.
You are already far beyond the need for using an entrainment product as a meditation aid. Those who sincerely believe this to be the case would not have come searching for a meditation site such as Project Meditation to help them learn and practice meditation and brainwave entrainment. They would probably not even bother with using an entrainment aid; hence this entire discussion would be irrelevant to them. The fact that you are here, reading this, seeking to benefit from incorporating meditation and brainwave entrainment to aid in your existing meditation practice suggests you are not one of these folks whose development is so advanced that entrainment is of no use to you.
As a trader, having focus is not a luxury, it’s a necessity for making the best decisions under pressure. The music and meditations allow me to bring my best game each and every day. I am more tuned into work for longer and better and with a steady energy and calmness. I am also a writer with a fairly high demand on output meaning I need to get a quality 700 to 1800 words of analysis created daily. And again I rely on to put my mind at it' most clear and creative. It delivers every time.
Anyone who has sought out different methods for enhancing cognitive ability will probably have come across a technique known as Brainwave Entrainment. However, it is a fairly niche area of brain training, meaning that this form of stimulation is often overlooked in favour of more mainstream methods. The following outlines what Brainwave Entrainment actually is, how it is used, and some of the benefits attributed to it.
It takes slightly more time to practice guided imagery, but this is a great way to leave your stress behind for a while and relax your body. Some find it easier to practice than meditation, as it allows more engagement of the conscious mind. You can focus on imagining relaxing environments you would love to visit, or on memories of your "happy place" for when you're stressed. You can play natural sounds in the background as you practice, to promote a more immersive experience.
Infra-Low brainwaves (also known as Slow Cortical Potentials), are thought to be the basic cortical rythms that underlie our higher brain functions. Very little is known about infra-low brainwaves. Their slow nature make them difficult to detect and accurately measure, so few studies have been done. They appear to take a major role in brain timing and network function. 
A crossover RCT of a single session of theta stimulation in four healthy adults reported no significant improvement in verbal fluency or attention associated with the intervention and a reduction in immediate recall. Controlled comparisons reported significant benefit from the intervention in all three outcomes measured. Six pre/post studies reported significant benefit from the intervention for 19 of 28 cognitive outcomes.