Det var ikke før prøvesangen at dirigenten hørte hele stemmeomfanget.

This is a very common Norwegian pattern meaning It was not until ... that ....

So:

• Det var ikke før prøvesangen at ... = It was not until the audition/tryout that ...

The structure puts special emphasis on when something finally happened.

A more neutral version of the same idea would be:

• Dirigenten hørte ikke hele stemmeomfanget før prøvesangen.

That means roughly the same thing, but the original sentence is more focused and dramatic.

Here det is a dummy/formal subject, just like English it in It was not until ... that ....

It does not refer to a specific thing. It is simply part of this sentence pattern:

• Det var ikke før X at Y skjedde.

So in this sentence, det is grammatical structure, not a word with much independent meaning.

In this structure, at introduces the clause that tells us what happened after that point.

So:

• Det var ikke før prøvesangen at dirigenten hørte hele stemmeomfanget.

Literally, it is something like:

• It was not until the audition that the conductor heard the full vocal range.

Here at works much like that in English. It is a normal part of this pattern.

Prøvesangen is the definite singular form of prøvesang.

• en prøvesang = an audition / a trial song / a tryout performance
• prøvesangen = the audition / the tryout performance

The definite form is used because the sentence refers to a specific event: the particular audition in the situation being described.

Prøvesang is a compound noun:

• prøve = test, trial
• sang = song / singing

Together, prøvesang usually refers to a singing tryout, audition, or test performance.

Depending on context, English might translate it as:

• audition
• tryout
• test singing

So even if the literal parts are easy to see, the natural translation is often audition.

Dirigenten means the conductor.

The definite form is used because the speaker has a specific conductor in mind, not just any conductor.

Compare:

• en dirigent = a conductor
• dirigenten = the conductor

In real narration, Norwegian often uses the definite form where English also uses the because the person is already identifiable from the context.

Stemmeomfanget means the vocal range.

It is another compound noun:

• stemme = voice
• omfang = range, extent, scope

So:

• stemmeomfang = vocal range
• stemmeomfanget = the vocal range

This is a very typical Norwegian compound: two nouns joined together to make one more specific noun.

Hele means whole or entire.

So:

• hele stemmeomfanget = the entire vocal range

This tells us the conductor did not just hear part of the singer’s range, but all of it.

The definite form stemmeomfanget is natural here because it refers to the singer’s full, specific vocal range. In Norwegian, hele + definite noun is very common:

• hele dagen = the whole day
• hele huset = the whole house
• hele stemmeomfanget = the whole vocal range

Because after at, Norwegian uses subordinate clause word order.

In a main clause, Norwegian normally follows the verb-second rule. But after a subordinating word like at, the clause is no longer a main clause, so the subject usually comes before the verb:

• at dirigenten hørte ...

If there were a negation inside that clause, you would also see typical subordinate order:

• at dirigenten ikke hørte hele stemmeomfanget

So the sentence is following normal Norwegian clause rules.

On its own, før often means before. But in the pattern ikke før ... at ..., the meaning becomes not until ... that ....

So:

• før prøvesangen = before the audition
• ikke før prøvesangen at ... = not until the audition that ...

This is a good example of how a word’s meaning can shift slightly inside a fixed structure.

Yes. A simpler version would be:

• Dirigenten hørte ikke hele stemmeomfanget før prøvesangen.

That is more straightforward and probably easier for a learner to build.

The original sentence:

• Det var ikke før prøvesangen at dirigenten hørte hele stemmeomfanget.

is more emphatic. It highlights the fact that the conductor only realized the full range at that particular moment.

So both are correct, but the original has stronger focus on the timing.