The google translation to English for the Chinese phrase (磁性的"聲音) is magnetic sound. Maybe try to google the words to help you understand the meaning, but the context in which you use the words is important too; as they could be construed as affectionate. But if you liked him you could say, "I think you have a magnetic voice and you are charming and attractive". I think this would be appropriate.

Hi! You could probably use magnetic, but don't use charming or attractive. They are a bit personal. You can simply say: "you have an incredible voice."