Nada dhyana

Sri Sadgurubhyoh Namah

VBT 41 :

Tantryaadivaadyashabdeshu deergheshu kramasamsthiteh,

ananyachetaah pratyante paravyomavapur bhavet

Translation :

The body becomes supreme space when one-pointed awareness is gradually developed on the inner sounds of different musical instruments like stringed, flute and percussion. 

The anahata nada dhyana explained about how to identify the uninterrupted inner sound. In this sutra it is explaining that when one-pointed awareness is gradually developed for a prolonged listening of these inner sounds like veena, flute, percussion etc, the body is experienced as the supreme space.