Correct vibrational intonation was an important emphasis within all aspects of Mantra initiation and there was a strict process in the transmission of a Mantra lest the vitality of the Mantra becomes increasingly diminished if the vibration is compromised at any level.
As with all aspects of a personal practice, Krishnamacharya and Desikachar taught Mantra within a private and individual initiation with a specific Vinyāsa Krama, which would mean that by the time it came to introduce the Mantra as a form of Japam the student was prepared and capable to both hold and sustain a mental consistency and vibratory resonance.
Hence the process of transmission had a precise Vinyāsa Krama from firstly oral, then to labial and finally mental. As an example, having progressed to working at the subtler levels with a particular Mantra relevant to my Sādhana at that point in our work, Desikachar would time me when observing that aspect of my practice to see that the mental recitation for say 108 recitations took exactly the same time as would the oral or labial recitation.
This was one of the checks to see if at least I had the metre correct amongst other things such as the vagaries of the mind mood corrupting the intonation. Of course this subtler level of practice observation would require that this inner practice would have been preceded by a careful learning of the oral form first.
This also meant that the rules of chanting Mantra were in place before getting to a point where the teacher would consider teaching Manas Mantra for a personal Sādhana. This is also why the learning of Mantra orally requires a precise understanding of the rules of chanting, something I observe as either an increasing sloppiness, or ignorance of the fundamental principles, around the Yoga world when coming across examples of oral chanting.
It doesn’t make sense also, as how do you verify that, if the oral is not clearly in place first? Lest the student mentally mutters whatever their mind interprets.
Equally in terms of using Mantra within Prāṇāyāma, if there is a sloppiness in the mental pronunciation then this will affect the ratio and thus the intention and outcome of the potential effect. Its like saying this is the ratio or the breath length that is required to induce a particular energetic or psychological effect but it doesn’t matter if its not perfect. Or, from my days as a Medical Herbalist, these are the ingredients or the quantities for the formula, but it doesn’t matter if the proportions change.
If the Mantra is not recited according to such rules as the appropriate Svara or Mātra, to name but two principles, then we change the mental effect. This is one of the reasons why, in the convention of Krishnamacharya, oral chanting was emphasised and taught rigorously to all interested in delving deeply into this ancient and profound mystical art.
Of course within this learning, it becomes obvious that the entire process of transmission need to take place within the private context of 121 lessons. Plus this also presumes that the Mantra selected by the teacher has a specific and personal reference to the students process and intentions.
Perhaps within a generalised group situation such principles are not possible to apply and especially verify, thus a looser context would be utilised in order to present a more broader taster context. For example if we compare with say Āsana practice there are a lot of visual clues as to the appropriate practice, whereas with Manas Mantra there is little to observe.
However from my own experience around both the theory and practice of Mantra, the same rigorousness would apply whether working with physical, respiratory or mental levels of the student. Though obviously, this attention to detail and performance would be tailored to the starting point and capacity of the student. Thus even compromising on ‘perfect’ would be done with an attention to detail according to the potential and long term interest of the student at that particular point in their learning cycle.
The reality in this transmission is that pronunciation and timing, amongst other aspects, does matter and the student needs to be firstly well trained in the gross or oral aspect prior to the subtler practices being introduced. This is an area that you cannot easily monitor externally, unlike say Āsana, hence we need to know that you are not building in errors from the word go.
Otherwise how is the student going to know its going wrong and self-correct it, if they have no reference. Thats why I would suggest that oral pronunciation is an application of Dhāraṇā and that mental pronunciation is an application of Dhyānam. On this note I would also suggest that the mispronunciation of the vibratory phoneme and timing of the metre can be potentially quite a problem if there is a general lack of teaching, or interest, around these core principles.