In this context, silent vibrations of the self (anhata), sound [and] music (ahata) carry a spiritual weight more meaningful, respectively, than what sensory properties normally provide.
Silent vibrations of the self (anhata) and Sound and music (ahata) are considered to play a potential medium/intermediary role to achieve a deeper unity with both the outer and inner cosmos.
Music has been used by some Indian saints as an important and powerful tool in the quest for the achievement of nirvana; notable names to be mentioned here include Kanakadasa, Thyagaraja, Kabir, Meerabai, Namdeo, Purandaradasa and Tukaram.
To concentrate on this inner sound (silent vibration of the self) as a support for meditation is very helpful to tame the mind, and when it has been clearly recognized, used for self-recollectedness in outer life as well.
In Nāda yoga, one of the main breathing sounds is ahaṃ (literally "I," referring to the inner essence, not ego), where each part of the word (a ha ṃ) is focused on and spoken individually.
[1] In the West, detailed indications and advice have been given by Edward Salim Michael in his book The Law of attention, Nada Yoga and the way of inner vigilance.
Jamgon Kongtrul (1813–1899) provides an important paradigm of salience for the esoteric Dzogchen doctrine of "sound, light and rays" (Wylie: sgra 'od zer gsum) and the 'mantra' of the Mantrayana tradition in particular, Kongtrul, et al. (2005: p. 431) identifies the “primordial sound” (nāda) and its semantic field: The primordial indestructible great vital essence (gdod ma'i mi shigs pa'i thig le chen po), which is the root or ground of all of cyclic life [samsara] and perfect peace [nirvana], is known as primordial (gdod ma) because it has no beginning or end; as indestructible (mi shigs pa) because it is indivisible; as vital essence (thig le) because it pervades the various appearances; and as great (chen po) because there is nothing that it does not encompass.
There are countless synonyms for the primordial indestructible great vital essence, such as "great seal" (phyag rgya chen po, mahāmudrā), "great bliss" (bde ba chen po, mahāsukha), "primordial sound" (nāda), "all-pervading vajra of space" (mkha' khyab nam mkha'i rdo rje), "ordinary awareness" (tha mal shes pa), "pristine awareness channel" (ye shes kyi rtsa), "pristine awareness wind" (ye she kyi rlung), "invincible ham" (gzhom med kyi ham), "invincible vital essence" (gzhom med kyi thig le), "essence of enlightenment" (sugatagarbha), and "transcendent wisdom" (she rab phar phyin, prajnā-pāramitā) (CPR, f.
[3] This quotation comes from the famed Sheja Dzö or 'The Treasury of Knowledge' (Tibetan: ཤེས་བྱ་མཛོད, Wylie: shes bya mdzod)[4] a voluminous work, encyclopedic in breadth, by Jamgon Kongtrul.
These quotes are from p. 91 and p. 93 respectively of "Masters of Mahamudra: Songs and Histories of the Eighty-four Buddhist Siddhas" by Keith Dowman, Publisher: State University of New York Press (ISBN 978-0-88706-160-8)