This is the 3966th most frequent Dutch word.
zacht
Soft.
Here, 'zacht' is used as an adjective to describe the physical texture or quality of the cushions.
De kussens op de bank zijn zacht.
The cushions on the couch are soft.
In this case, 'zachte' (inflected form of 'zacht' due to grammatical agreement with 'stem') describes the gentle and soothing quality of the speaking voice.
Ze sprak met een zachte stem.
She spoke with a soft voice.
Here, 'zacht' refers to the dim or mellow quality of the lighting in the room.