Chanting of Vedic Mantras

In the chanting of Vedic mantras, the pitch and amplitude should be perfect. The chanting of different mantras creates vibrations and thus sound.
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Breathing patterns differ based on moods and tempers. Happiness arising as a result of religious practices or Bhajans is different from that caused by the satisfaction of desires of senses. Generally, the higher type of happiness results in exhalations through the right nostril. More sensory pleasure activates breathing out through the left nostril. All sensations are synthesised when thought is centred round a noble cause.
The passage of breath through various nerves creates vibrations which are responsible for the health of beings. With every kind of emotion, a different set of vibrations are caused to the nerve centre. Emotions caused by the mind result in the change of one’s pulse beat. By controlling the pulse beats and rhythms of breathing, we can exercise control over passion or anger. Parnayama is thus chief instrument in the control of the mind.
Similarly, Mantra Yoga is another path. When we utter a word, the life breath is allowed to pass through the gaps in the throat, tongue, lips, mouth etc. Only then the sound of the word emanates and becomes audible. Vibrations are caused to the nerve centres situated in these areas through which breath passes to produce the sound of the word.  Veda mantras properly recited with the proper discipline produce the necessary emotions in the mind which ensure well-being to the person reciting as well as to the world.
Learned people consider six methods of recitation, as not correct and advise to be avoided: -

1. Chanting in a sing-song fashion.  Though Samaveda is musically recited, it can be recited only in the approved musical way.
2. Chanting in a quick tempo. Vedic words should be intoned by closely adhering to the time limits prescribed for uttering each word sound.
3. Shaking and nods of head. One should sit straight in concentration and allow the pulse vibrations to occur naturally by themselves. Nodding of the head disturbs the vibrations.
4. Reading from the written script. Chanting from memory in proper manner.
5. Chanting of mantras with knowing the meaning of the words in order to have the full beneficial effect.
6. Recitation in a feeble voice. Vedic mantras must be chanted with grandeur, so that the sound can be properly heard. Vedic mantras not only produce beneficial vibrations in the pulse of the one who chants them properly but also similar vibrations in those who may hear them. Since it is spread in the atmosphere, it ensures well-being here and thereafter. Chanting of Vedic mantras results in individual as well as collective well-being of the world.

Reference - The Vedas – by Pujasri Chandrasekharendra Saraswathi