Det var ikke før neste korøvelse at sopranen fant riktig tonehøyde.

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

So:

Det var ikke før neste korøvelse at sopranen fant riktig tonehøyde.

means something like:

It wasn’t until the next choir rehearsal that the soprano found the right pitch.

The structure is:

• Det var ikke før X at Y skjedde
• literally: It was not before X that Y happened
• naturally: It was not until X that Y happened

This pattern is often used for emphasis.

Here det is a grammatical subject, similar to English it in sentences like:

• It was not until later that I understood.
• It was yesterday that she called.

In Norwegian, det is often used in this kind of cleft-like or emphasizing structure:

• Det var ... at ...

It does not refer to a specific thing here. It is just part of the sentence pattern.

Yes, før basically means before, but in the expression ikke før ... at ..., the whole pattern means not until.

Compare:

• før klokka tre = before three o’clock
• ikke før klokka tre = not until three o’clock

So in this sentence:

• ikke før neste korøvelse = not until the next choir rehearsal

This is one of those cases where you should learn the full expression, not just the individual word.

Because at introduces the clause that tells us what happened at that time.

Structure:

• Det var ikke før neste korøvelse = the time phrase being emphasized
• at sopranen fant riktig tonehøyde = what finally happened

So at here works like that in English:

• It wasn’t until the next choir rehearsal that the soprano found the right pitch.

In everyday English, that is often optional, but in Norwegian this at is normally included in this structure.

Because with words like neste, Norwegian often uses the noun without the separate definite article when the meaning is general or time-related.

So you commonly get:

• neste uke = next week
• neste gang = next time
• neste korøvelse = the next choir rehearsal

You can sometimes see fuller definite forms in other contexts, but neste korøvelse is very natural here.

A useful thing to remember is that time expressions often behave a bit more simply in Norwegian.

Sopranen is the definite form, meaning the soprano.

• en sopran = a soprano
• sopranen = the soprano

The sentence is talking about a specific soprano, not just any soprano. That may be because the person has already been mentioned, or because the context makes clear which soprano is meant.

Korøvelse is a compound noun:

• kor = choir
• øvelse = rehearsal / practice

Together:

• korøvelse = choir rehearsal

Norwegian forms compound nouns very freely, and they are usually written as one word. This is much more common than in English.

Other examples:

• skolebok = school book
• sommerferie = summer holiday
• tonehøyde = pitch

So korøvelse is completely normal Norwegian spelling.

Fant is the past tense of finne, which means to find.

The forms are:

• å finne = to find
• finner = find / finds
• fant = found
• har funnet = have/has found

So:

• sopranen fant = the soprano found

Tonehøyde means pitch in the musical sense.

So:

• riktig tonehøyde = the correct pitch / the right pitch

Breaking it down:

• riktig = correct / right
• tonehøyde = literally something like tone height

In music contexts, tonehøyde is the normal word for pitch.

Because riktig is modifying a singular indefinite noun:

• en tonehøyde = a pitch
• riktig tonehøyde = correct pitch

In Norwegian, adjectives usually take -e in definite forms and plurals, but here the noun phrase is indefinite.

Compare:

• riktig tonehøyde = correct pitch
• den riktige tonehøyden = the correct pitch

So if the phrase had been definite, you would expect riktige.

Yes, absolutely. That version is also natural.

• Sopranen fant ikke riktig tonehøyde før neste korøvelse.
• Det var ikke før neste korøvelse at sopranen fant riktig tonehøyde.

They mean almost the same thing, but the second version is more emphatic. It highlights the timing more strongly: not until the next choir rehearsal.

So the original sentence is chosen to emphasize when it finally happened.

Not especially. After at, Norwegian uses subordinate clause word order, and in this sentence that looks quite normal:

• at sopranen fant riktig tonehøyde

That is:

• subject: sopranen
• verb: fant

Because there is no sentence adverb like ikke inside that clause, you do not see the most obvious subordinate-clause word-order effect here.

For example, compare:

• main clause: Sopranen fant ikke tonen
• subordinate clause: at sopranen ikke fant tonen

So the clause in your sentence is straightforward and normal.

Not exactly.

• tone can mean note, tone, or sound
• tonehøyde specifically means pitch

In music, finne tonen can sometimes mean find the note or get the pitch right, but finne riktig tonehøyde is more precise. It focuses specifically on pitch accuracy.

So tonehøyde is the more exact musical term here.