He showed us a letter from a student who studied Ethnomusicology - —the study of music from the cultural and social aspects of the people who make it. He showed us a letter from a student who studied Ethnomusicology—the study of music from the cultural and social aspects of the people who make it.

Nobody normally cares about this, but in case you're interested, I pasted in an m dash (—) there, which is what would be there instead of a hyphen in a print version.

I have never heard of this subject before,; it sounds very cool. I have never heard of this subject before; it sounds very cool.

Either the comma needs a joining word (such as "before, and it sounds") or it needs to be a semi-colon.

My knowledge of music theory and history were so poor that I was afraid I wouldn't understand this talk, but that didn't happen. My knowledge of music theory and history were so poor that I was afraid I wouldn't understand this talk, but that didn't happen.

I think it sounds more natural with "knowledge of" inserted

The topic is about "Soundscape", which means the acoustic environment as perceived by humans. The topic is "Soundscape", which means the acoustic environment as perceived by humans.

Or: the discussion is about "Soundscape" Or: the webinar is about "Soundscape" Or: the theme is "Soundscape" You have shifted from past tense to present tense here, but I think that is deliberate

The song beginning at 4'33'' is the most famous example. The song beginning at 4'33'' is the most famous example.

I am guessing that this is what you mean

The song is composed by John Cage, which is known for not to play their instrument during the entire duration of the piece. The song is composed by John Cage, which is known for not to play their instrument during the entire duration of the piece.

I'm not sure what is the antecedent of "which". If it is "John Cage" then it must be "who". Let me propose two versions, depending on which ("the song" or "John Cage") is the antecedent of "which". The song is composed by John Cage, who is known for writing pieces with no instrumental parts for the entire duration of the piece. Or The song, composed by John Cage, is known for having no instrumental play for the entire duration of the piece.

It only consists of the sounds of the environment that the listeners hear whilduring the performingance. It only consists of the sounds of the environment that the listeners hear during the performance.

"listeners hear while performing" implies that the listeners are performing, which I don't think is intended

The lecture gave many examples of environmental sounds, such as the screaming promoads of vendors on the street, the sound of neighbors going out regularly, and so on. The lecture gave many examples of environmental sounds, such as the screaming ads of vendors on the street, the sound of neighbors going out regularly, and so on.

The lecture also highlighted the fact that a religion in some areas plays a uniformregular radio reading of the scriptures in the morning. The lecture also highlighted the fact that a religion in some areas plays a regular radio reading of the scriptures in the morning.

I think you meant a "regularly scheduled reading", which can also be said as a "regular reading"

To be honest, it reminded me of the school bell. To be honest, it reminded me of the school bell.

Your sentence is fine, but I don't understand what "it" refers to. The religious reading?