स घोषो धार्तराष्ट्राणां हृदयानि व्यदारयत्।नभश्च पृथिवीं चैव तुमुलो व्यनुनादयन्॥
sa ghoṣo dhārtarāṣṭrāṇāṃ hṛdayāni vyadārayatnabhaśca pṛthivīṃ caiva tumulo nunādayan
Word by word
The verse says
That tumult, thundering through earth and sky, tore the hearts of Dhritarashtra's sons.
In plain words
The sound does damage before a single arrow is fired.
It fills the space between earth and sky, and it breaks something in the men on the other side. The verb is strong — it tore their hearts.
No one has been touched. The battle has not begun. And one army is already coming apart.
Where you've felt this · in family life
The particular silence in a house after raised voices stop. Nothing has been broken and nobody has left, but everyone can tell that something has been decided, and that it will not be taken back.
Going deeper
This is where the chapter turns, and it turns on morale rather than on force.
Until now the poem has been counting: this many warriors, that many great archers, our strength against theirs. Duryodhana built his whole speech out of that arithmetic. Then a noise crosses the field and the arithmetic stops mattering, because the men it describes have lost their nerve.
The Gita will keep returning to this. What decides an outcome is rarely the inventory. It is the state of the mind holding the weapon. Chapter 6 puts it bluntly: you are your own friend or your own enemy, and nobody else gets a vote.
Notice as well that the Kauravas break at a sound while Arjuna, in a few verses, will break at a sight. Both armies lose their composure in this chapter. Only one man asks anybody about it.