Music can be assur for a few different reasons.
1. Avodah Zara- It is assur to listen to music (even classical music) written for the sole purpose of worship of other gods. Church music for example.
2. Hirhurim- It is assur to listen to (most modern) music whose main theme is lewd discussion of relationships. It is a terrible thing to be influenced by those values which are so antithetical to our holy Torah. The Torah believes that these issues should not be discussed so publicly and in a way that portrays these matters as simply self- pleasure. It lacks any form of busha and takes away from the kedusha possible to achieve by using these tayvas at the proper time. Listening to this type of thinking definitely causes us to spend time thinking about these issues which is assur and it is also tremendously distracting as it tends to take over people’s entire mind.
3. What’s the problem with other music? I wouldn’t say it’s necessarily the best use of one’s time, but I don’t see the problem.
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