Question

what is mean by low pitch

Answer 1

low-pitched. ... People who sing inlow registers — altos and basses, for example — have low-pitchedvoices, and a big dog might have alow-pitched bark, especially compared to your toy poodle's yap. This definition of low-pitchedcomes from the sense of pitchthat means "the highness or lowness of a sound's tone."
Oftrn produced by slow vibrations