OUT LOUD, UNDER YOUR BREATH OR PURELY MENTALLY.
Both David Frawley and Thomas Ashley-Farrand record some of the traditional points on where, when and how to do mantra work. This article relates more to the central theme of the chanting itself. There are sources which say that chanting out loud is the least effective way to repeat mantra. Recitation can also be done under one’s breath, or even purely mentally. The idea that purely mental recitation is the best way to repeat mantra, follows what I suggest is intellectual snobbery on the part of whoever put forward such a theory, and let us remember that there is a huge divergence of opinion on matters yogic in the texts from India; one respected author may say one thing and another respected author may put forward the opposite case.
Even if you do not make a sound you are still registering the memory of a sound when you recall it, haphazardly or deliberately. Why are mantras often turned into kirtan if they are said by some to lose their power when spoken out loud? Of course if you have been given a specific mantra by a teacher then it may well be best for you not to say it out loud. The teacher should advise you on this. That kind of mantra transmission lies in the field of a very personalized sadhana. A much cited rule relays that if you undertake a very particular piece of subtle work, you should not talk about what you are doing, because talking about it to others can make you lose focus. Focus is very important.
Up until 2019 my mantra practice was over 50% done under my breath. Now it is almost exclusively done out loud. Maybe that is because I am a drummer and singer. The main thing is to see what works for you. There is a beauty in NOT using the voice in my experience, it may allow the mantra to work differently from when the ears are hearing clear strong sounds as the mantra is recited. It would be interesting to hear from people who recite purely mentally, why they use that method, and what they get from it.