choyeoneseo hyogwa-eumeul cheoeum deureosseo.

Korean often leaves out the subject when it is clear from context.

So 초연에서 효과음을 처음 들었어 naturally means something like:

• I heard the sound effect for the first time at the premiere
• or, depending on context, we/they heard...

In everyday Korean, pronouns such as 나 or 저 are often omitted unless they are needed for emphasis or clarity.

초연 means the premiere or the first public performance/showing of something.

So 초연에서 means at the premiere or during the premiere.

A learner might notice that 초 often relates to first/initial, and that fits here:

• 초연 = first performance, premiere

에서 marks the place or event where an action happens.

Here, the action is hearing something, so 초연에서 means:

• at the premiere
• during the premiere
• in the context of the premiere event

Compare:

• 학교에서 공부했어 = I studied at school
• 초연에서 들었어 = I heard it at the premiere

A native English speaker might wonder why not 에. In many cases:

• 에 is often used for destination, time, or existence
• 에서 is used for where an action takes place

Since hearing is an action, 에서 makes sense.

효과음을 = 효과음 + 을

• 효과음 = sound effect
• 을 = object marker

So 효과음을 means the sound effect as the thing that was heard.

Because 효과음 ends in a consonant, it takes 을 rather than 를.

Examples:

• 음악을 들었어 = I heard music
• 효과음을 들었어 = I heard the sound effect

Here, 처음 means for the first time.

In 효과음을 처음 들었어, 처음 works adverbially and describes the action 들었어:

• 처음 들었어 = heard it for the first time

This is very natural Korean.

A literal English-style gloss might be:

• At the premiere, I heard the sound effect for the first time

So here 처음 is not really the first one in a sequence. It is about first experience.

This is a very common question.

• 처음 often means for the first time
• 처음에 often means at first or in the beginning

So:

• 효과음을 처음 들었어 = I heard the sound effect for the first time
• 처음에 효과음을 들었어 would sound more like At first, I heard the sound effect or I heard the sound effect first, depending on context

In this sentence, the meaning is about first experience, so 처음 is the natural choice.

This comes from the verb 듣다 = to hear/listen.

It changes irregularly:

• dictionary form: 듣다
• stem used before a vowel-like ending: 들-
• past informal: 들었어

This is because 듣다 is a ㄷ irregular verb.

Common forms:

• 듣다 = to hear/listen
• 들어 = hear / listen
• 들었어 = heard
• 들어요 = hear / listen / heard in polite speech depending on context
• 들었어요 = heard

So 들었어 is simply heard in casual speech.

들었어 is a casual, informal ending.

It would be used:

• with friends
• with younger people
• in casual narration
• in diary-like or conversational language

More polite versions would be:

• 초연에서 효과음을 처음 들었어요.
• 초연에서 효과음을 처음 들었습니다. (more formal)

So the grammar is the same; only the speech level changes.

The verb 듣다 can cover both hear and listen, depending on context.

In this sentence, 효과음을 처음 들었어 most naturally means:

• I heard the sound effect for the first time

Because sound effect is something perceived by the ears, English usually translates it as heard here.

But in other contexts, 듣다 can mean listen to:

• 음악을 듣다 = to listen to music
• 이야기를 듣다 = to hear/listen to a story

So the exact English wording depends on context.

It is possible to imagine that reading for a moment, but the most natural interpretation is for the first time.

That is because 처음 들었어 very commonly means heard it for the first time.

If someone wanted to clearly mean first in sequence, Korean would often use something like:

• 먼저 들었어 = heard it first
• 처음에 들었어 = heard it at first / initially

So in normal context, this sentence is understood as:

• I heard the sound effect for the first time at the premiere

Yes. Korean word order is flexible as long as the particles make the relationships clear.

For example, these are all possible with slightly different emphasis:

• 초연에서 효과음을 처음 들었어.
• 효과음을 초연에서 처음 들었어.
• 처음 초연에서 효과음을 들었어.
  This one is less natural for the intended meaning, though, because 처음 is usually placed close to the verb it modifies.

The original order is very natural because it flows like this:

• setting: 초연에서
• object: 효과음을
• manner/time nuance: 처음
• verb: 들었어

That is a common and clear Korean structure.

You could say:

• 나는 초연에서 효과음을 처음 들었어.
• 제가 초연에서 효과음을 처음 들었어요.

The choice depends on tone:

• 나는 = I, with topic emphasis, casual
• 제가 = I, subject emphasis, more polite or contrastive

But in many real situations, Korean would still omit the subject unless there is a reason to include it.