Comtemplating on sacred sounds or chanting mantras aloud, is on of the most ancient ways of practicing yoga. Behind all the mantras there's one sacred syllable ~ Om ~. It's considered the direct way to connect with the divinity in us. By contemplating and by repeating it, we will open new doors within ourselves. The sacred sound changes our ordinary consciousness to a higher consciousness.
Chanting is a very appropriate and efficient way to prepare one's mind for the meditation. In Ashtanga yoga chanting is considered as a Pratyaya (sensual peace) practice which contributes to entering a state of restful alertness. When the senses are not going outwards as they usually do, they provide the mind less information and the mind can rest. This creates a peaceful, vigilant, no-mind state.
The call and response technique is the traditional method to learn to chant. The students repeat after the teacher once or twice or even many times the same sentence to learn to pronounce the Sanskrit language correctly and to memorize the sentence. Once you know the text by heart, you go deeper in a relaxed state. The chanting becomes very easy and pleasant and creates strong positive vibrations inside the body and around it. It feels like the sounds are just flowing out of you without any effort. In my workshops I teach some mantras and the Yoga Sutra of Patanjali. The Yoga Sutra chanting is often combined with the teaching of Patanjali's yoga philosophy, explanation of what has been chanted.
For the beginners this practice requires a very alert state to listen to what is said and to repeat it. When you are not familiar with the Sanskrit language, your effort is to try to discern the individual phonemes and to repeat the long words. This effort makes it impossible to think of anything else. You don't have time to think and repeat, you spontaneously say what you just heard. You learn to listen really carefully.
My teacher in chanting is M.A. Jayashree who lives and teaches in Mysore, India. I've learned many mantras, Yoga Sutras, Bhagavad Gîta and some parts of Upanishads with her.