The different kinds of Japa are
1. Vaikhari Japa (audible)
2. Upamsu Japa (whispering)
3. Manasika Japa (mental)
4. Likhita Japa (written)
In Tantra a lot of emphasis is laid on Japa. For attaining Mantra Siddhi you have to do Japa of the mantra a particular number of times. But it is not that you stop with that. You are expected to do constant Mantra Japa so that the Mantra becomes part of you. The Mantra is always running in your mind. In Tantra the rituals are necessary for only the main Japa when you count. But otherwise you are free to do Mantra Japa without any restrictions.
The same attitude is taken in Nama Japa also where the Nama becomes part of you. Here here is no emphasis on the count. Still many traditions insist that you should do minimum number of times per day. This is to ensure that you do it regularly. It is good if you decide the minimum number that you will recite per day.
In Japa you progress from Audible Japa to Mental Japa over a period of time.
There is very little difference between Mental Japa and Meditation
Most of the Hindus know about prayers, and Nama Japa well, as these are part of the daily ritual. Though the term Dhyana (Meditation) is known, wherever it is mentioned Dhyanam we just said Dhyanam or recited what is called Dhyana Sloka of the Deity.
Meditation as is now known was only for the very few. I have not heard of anyone doing meditation in my village full of Brahmins. Meditation was associated with Tapas, which meant that it was beyond the reach of the common man. Because meditation was equated almost with Tapas, only those Hindus who were deeply spiritual took to meditation. Mostly these were Sanskrit scholars and students of Philosophy.
Meditation became popular in India mainly due to Bagavan Sri Ramakrishna, Bagavan Ramana Maharshi and Swami Sivananda. However it is still largely confined to the English knowing population. In India Bhakthi and rituals are considered superstition by the English educated intellectual class. Many of these people took to Meditation.
When my father was a student of Swami Sivananda in the early 50s what he learnt was mainly Hatha Yoga, Japa and Hindu Philosophy. Swami Sivanananda's books give a lot of emphasis on Japa. Even In Hatha Yoga though we were taught all the Asanas, we were asked to do only Sirasasana , Sarvanghasana and other simple asanas daily. Even Sirasasana was to be done only if it suited you. Again Pranayama was learnt only through an experienced teacher. Sri. Kali Ghosh who was my teacher was very particular that I follow all the rules and also checked my progress regularly.
Though the development was like this in India, in the west it was the other way around. Meditation became almost synonymous with Hinduism. I saw someone writing that Meditation is Hinduism.
When we attend a course in Mountaineering, you are first taught rock climbing and then taught how to climb small mountain peaks. You do not expect to climb Mount Everest just by attending one Mountaineering course. You become proficient in rock climbing, climb a couple of peaks in the Alps, and then try the minor peaks in the Himalayas before attempting Mount Everest. Even in that I can never progress as fast as a man from Ghatwal because he is from the mountains and his heart is already accustomed to heights.
The reason why I am writing all this is that I find that, though in India we progressed slowly from prayer to Meditation over a period of years, most people in the west are directly initiated into meditation. It is my view that for most people it is like trying to climb Mount Everest without ever having done even rock climbing. Many of the instructions given for spiritual aspirants by Swami Sivanananda have been part and parcel of our daily life for generations.
Am I saying that all the courses in Meditation are fake? Definitely not. But if you are in New York and you attend a course in Rishikesh India you may have problems. If you stay in Rishikesh for six months then you have a better chance of success. Even then when you come back to New York you may have problems and you would not have anyone to discuss your problems. During my last visit to Dharamshala I found that for there are many people from outside India who come there regularly. These are people who are very serious students and practioners of Buddhism.
Similarly we find many people visiting India regularly. Even Swamijis who have reached great heights visit India regularly for spiritual regeneration.