Shannon - Masked track volume question

[Shannon]

I can only reasonably answer that question with certainty if I know the state of volume of audio entering your ears outside of the earbuds as it compares to the subliminal audio itself, because if the difference exceeds roughly 80 dB, the external audio will overpower the subliminal audio.

Given this, I would calibrate the masked track to be at least faintly audible against the background noise. Specific dB is impossible for me to know because I don't know what the audio externally is volume wise.