Quick answer
Vaikhari japa is spoken aloud, upamshu japa is whispered so the lips barely move, and manasika japa is recited silently in the mind. Traditional teaching holds each to be far more powerful than the one before, and treats them as stages: most people begin aloud and let the voice draw inward over time.
The Sanskrit root of japa, jap, means to utter in a low voice, to repeat inwardly, to mutter. Even the word leans towards quiet. The tradition describes three degrees of that quiet, and the difference between them is not volume alone.
वैखरीVaikhari: aloud
Vaikhari japa is spoken loud enough that someone near you could hear it. It is where most people begin, and for good reason: the sound gives the wandering mind something to hold. If you are new to the mala itself, start with how to do japa with a mala. It suits group chanting, a noisy room, and the days when attention will not settle. Some teachers consider chanting loudly to cover other noise a mistake; the point of the voice is to anchor the mind, not to compete with the world.
उपांशुUpamshu: whispered
Upamshu japa is said at a whisper, the lips barely moving, so that someone watching can hardly tell anything is being said. Traditional teaching says it is a hundred times more effective than vaikhari. It is the voice of most daily sittings, and the one you can keep on a bus or at a desk without anyone noticing. See japa on a commute.
मानसिकManasika: in the mind
Manasika japa is recited silently, in the mind alone. The same teaching holds it to be a thousand times more effective than upamshu, and so a hundred thousand times more than spoken japa. It is also said to be difficult, even impossible, for someone not already grounded in the spoken and whispered forms. That is the honest catch: silent japa is easy to start and hard to keep, because without the voice there is nothing to notice when the mind drifts away. The mala, or a counter you can feel, matters most here. It is the only sign that the japa is still going on.
Why quieter is held to be deeper
Japa is not the repetition of words but contemplation on the meaning of the mantra.
Patanjali is quoted as saying that japa is not the repetition of words but contemplation on the meaning of the mantra. Read that way, the three voices are stages of turning inward. It is also why a short naam such as Radhe Radhe and a long verse such as the Gayatri feel so different in silence: the longer the mantra, the more there is to hold in mind. Spoken japa engages the tongue, the ear and the mind. Whispered japa drops the ear. Silent japa leaves only the mind and the mantra. The less there is between you and the mantra, the closer the practice comes to what Patanjali describes.
Two more forms
Likhita japa is writing the mantra, usually while saying it aloud, in a notebook kept for the purpose. Notebooks for short mantras have a grid of small cells, one mantra to a cell, and some people use different coloured ink to make a pattern across the page. Its proponents consider it more effective than speaking the mantra alone. It certainly holds attention: the hand, the eye and the voice are all at work on the same words.
Ajapa japa, literally "repetitionless repetition", is what traditions describe as the fruit of long practice: a state in which the mantra repeats itself in the mind, without effort. It is not a technique to attempt but something that is said to arrive.
Moving from one to the next
There is no schedule. Begin aloud if that holds your attention; let the voice soften when it no longer needs to be loud; try a round in silence when the whisper feels steady. If silent japa keeps dissolving into thought, go back to the whisper without any sense of failure. You can also use all three in one sitting: aloud to settle, whispered for the body of the practice, silent for the last round.
Frequently asked questions
Which type of japa is best?
Traditional teaching ranks manasika (silent) above upamshu (whispered) above vaikhari (aloud). It also says that silent japa depends on being grounded in the other two, so the best japa for you is the one you can keep with attention today.
Can I do japa silently while counting on a mala?
Yes, and the mala helps most in silent japa, because touch is the only sign that the japa is still going on. A counter that ticks under your thumb does the same job.
What is ajapa japa?
"Repetitionless repetition": a state described in many traditions where, after long practice, the mantra continues by itself in the mind.
What is likhita japa?
Writing the mantra, usually while saying it, in a notebook kept for japa.
Sources
Begin your next mala.
Japo is a japa counter that feels like the real thing. Pull a bead with your thumb, feel a soft tick, and pick up exactly where you stopped. Counting, history and goals are free.