Bhashya
तथा स्तनयित्नुः ।शब्दे भवः शाब्दः अध्यात्मं यद्यपि,तथापि स्वरे विशेषतो भवतीति सौवरः अध्यात्मम् ॥
In plain words
It is the same with thunder. What is born in sound is, in general, your inward counterpart — but it shows up most sharply in tone itself. So the more exact name for it, within you, is the tonal one.
Close to the Sanskrit
So too the thunder. In sound, the śābda [sound-born one] is, with reference to the self, though [it is present generally]; nevertheless, since it becomes especially [present] in tone, the tonal one [sauvara] is [named] with reference to the self.