i tried to collect some info on this subject
There are four types of mantras. They are veda mantras (mantras
chanted with shruthies which are taken from vedas). purana mantras
(mantras which do not have any shruthi and taken from 18 puranas or 18 upapuranas), itihaasa mantras (mantras which are taken from epics – either Mahabharata or Ramayana) and karma mantras (which are literal explanation of what we are doing i.e., karmas / it can also be a prayer). There is a belief that
veda manthras should not be chanted by everyone. This belief sprouted
only because, veda mantra chanting has ten difficult sruthies (udaattha, anudaattha, swaritha, repha, hraswa, pracheya, anunaasika, kampa, deergha kampa and plutha ). It takes years together for anyone to learn the veda mantras with shruti . Learning should be started from very young age itself, like 5 / 6 year old. Learning veda with shruthi is not that easy and veda mantra should be chanted with shruthi, because the shruthi is as important as the message of vedas. Hence, vedas are also known as shruthies. If one is chanting without shruthi, it is not good. It may be compared like taking five saridon tablets when we do not have a headache. It can cause more negative effect than giving positive effect. Hence it is instructed that everyone should not chant veda mantra . Anyone including Hindu , Christian, Muslim or following any religion and even ladies can chant veda mantra provided, they can chant with shruthi. I am specifically explaining the above statement because, veda mantras are not written by brahmins, they were composed by kashatriyas, veda mantras are divided by a non Brahmin, into four classes from fishermen (vyaasa kula) family, veda vyasa, The aacharass were not written by brahmins but maheedaasa aitareya who is from chandaala family. Many of our great rishies both modern and ancient are not Brahmins. This is true even in the case of avataaras. Lord Krishna and Rama did not belong to brahmin class. Thus one need not worry too much about the caste / religion /place of origin etc., for learning the vedas. They should only ascertain , whether they have the endurance power to sit and learn the vedas for about five years, uninterrupted. Remember, if the shruthi has gone wrong, even the meaning and the message changes and even becomes negative. Example: in gaayatri manthra ‘..dhiyo yo na: prachodayaath’. Here, the word /letter ‘na:’ if not properly chanted will give the meaning NO instead of US. i.e., ‘Oh lord Sun do NOT enlighten with dhaarmic wisdom’ instead of ‘Oh
Lord Sun enlighten us with dharmic wisdom’. I would like to inform you that every instruction given by our Rishies has a specific logic in that. Unfortunately due to our ignorance and biased approach we think they are all superstition. Remember that none is compelling us (including a Brahmin) to learn the vedas. If we are learning follow the instructions. This is what they said, but we misinterpret their instruction and say, it is savarna aadhipatya and superstition, etc. Detailed studies have been carried out by professors of music from
University on the vedic shruthies. Even today lot of research work is going on in this subject. The shruti of all the four vedas vary and that of Saama Veda is completely different. Veda trayee means vedas have been written partly as poems (padya style), prose (gadya style) and Music (geetha/gaana). This is the actual meaning of veda thrayee. (Some people think that veda thrayee means Rig veda, yajurveda and saama veda. They wrongly say atharva veda is not to be included . This is a superstition or mistake.