This is the 10973rd most frequent French word.
perceptible
Able to be perceived or noticed.
Here, 'perceptibles' is used adjectivally to describe signs that are hardly noticeable or detectable, providing a context of subtle observation.
Les premiers signes du printemps sont à peine perceptibles.
The first signs of spring are barely perceptible.
In this sentence, 'perceptible' is employed to indicate that the change in attitude was noticeable by attentive observers with familiarity.
Son changement d'attitude était perceptible pour ceux qui le connaissaient bien.
His change in attitude was perceptible to those who knew him well.
'Perceptible' here describes the background music as recognizable despite physical barriers, emphasizing sensory reception.