This is the 632nd most frequent Korean word.
목소리가
"목소리가" means "voice is" in English.
Here, '목소리가' means 'the voice,' specifically attributing it with the quality of gentleness, indicating it refers to the vocal tone of the teacher.
선생님의 목소리가 부드럽네요.
The teacher's voice is gentle.
In this sentence, '목소리가' signifies 'voice' and emphasizes the inability to hear it, denoting the sound generated by the individual.
그녀의 목소리가 들리지 않아요.
I can't hear her voice.
Here, '목소리가' refers to 'voice' again, relating it to the singer's vocal ability and its aesthetic quality.