Shiva is also often referred to as "Shabda Brahman" or "Nada Brahman" due to his association with sound (Om) and vibration (damaru).
In Hindu philosophy, the term "Brahman" refers to the ultimate reality or the absolute. It is considered to be formless, transcendent, and beyond human comprehension. It is the source and essence of all existence.
Om came into existence from the 5 sounds that came from Shiva's Five Face the combined form of those 5 sounds is Om or Omkara or Pranava
Sound, in the form of vibrations and energy, is believed to be the fundamental aspect of creation. According to Hindu cosmology, the universe originated from the primordial sound or vibration known as "Om" or "Aum." This primordial sound is considered to be the manifestation of the divine and the source of all other sounds.
Shiva is often depicted as Nataraja, the Lord of Dance, where his cosmic dance symbolizes the rhythm and movement of the universe. His dance is believed to create and sustain the universe, and the sound produced by his drum, known as the "damaru," represents the primal sound of creation.
Shiva's association with sound and vibration is further emphasized in his portrayal as "Nada Brahman" or the divine sound. Nada refers to the subtle sound or vibration that pervades the entire universe. It is considered to be the essence of all sounds and the underlying principle of creation.
By being called "Shabda Brahman" or "Nada Brahman," Shiva is acknowledged as the embodiment of the ultimate reality that is beyond form and comprehension. He represents the primal sound and vibration from which all creation arises, symbolizing the profound connection between sound, consciousness, and the divine.
The Mandukya Upanishad begins with this verse
ॐ इत्येतदक्षरमिदꣳ सर्वं तस्योपव्याख्यानं भूतं भवद् भविष्यदिति सर्वमोङ्कार एव यच्चान्यत् त्रिकालातीतं तदप्योङ्कार एव ॥ Means Past Present Future Everything is Om OM which transcends three division of time.
In Vidyeśvara-saṃhitā [ Chapter No -10 ] of Shri Shiv Mahapurana, Mahadev (Lord Shiva) explains the significance of his 5 Faces and pañcakṛtya & Oṃkāra-mantra to Lord Vishnu & Lord Brahmā.