Det var ikke før hele koret sang at vi hørte samklangen.

This is a very common Norwegian pattern meaning It wasn’t until ... that ....

So:

• Det var ikke før hele koret sang at vi hørte samklangen
• = It wasn’t until the whole choir sang that we heard the harmony/blend

This structure is used to emphasize that something only happened at a particular point, and not earlier.

A simpler way to think of it is:

• ikke før X at Y
• = not until X that Y

Here, det is a formal or dummy subject. It does not refer to a specific thing like it often does in English.

Norwegian often uses det in fixed sentence patterns, especially in:

• cleft-like structures
• impersonal expressions
• emphasis structures

In Det var ikke før ... at ..., the det is just part of the standard construction. You should usually learn the whole pattern together rather than trying to translate det by itself.

Because the sentence is talking about a past situation.

• var = past tense of å være
• er = present tense

So:

• Det var ikke før ... at ... = It wasn’t until ... that ...
• Det er ikke før ... at ... would mean It isn’t until ... that ..., referring to the present or a general situation

Since hørte and sang are also in the past, var matches the tense of the whole sentence.

Here sang is a verb, the past tense of å synge (to sing).

• å synge = to sing
• synger = sings / is singing
• sang = sang
• har sunget = has sung

So:

• hele koret sang = the whole choir sang

It is not the noun song here. In Norwegian, sang can also be a noun meaning song, but in this sentence the grammar clearly shows it is a verb.

Because hele koret means the whole choir.

• kor = choir
• koret = the choir

When hele means the whole, it commonly goes with a definite noun:

• hele dagen = the whole day
• hele huset = the whole house
• hele koret = the whole choir

So hele koret is the natural way to say the entire choir / the whole choir.

In this pattern, at introduces the clause that tells us what finally happened.

So the sentence breaks down like this:

• Det var ikke før hele koret sang
• at vi hørte samklangen

Literally:

• It was not until the whole choir sang
• that we heard the harmony

In English, that is sometimes optional in similar sentences, but in Norwegian at is a normal and important part of this construction.

Because at introduces a subordinate clause, and subordinate clauses in Norwegian usually have normal subject-verb order:

• at vi hørte
• = that we heard

So:

• vi = subject
• hørte = verb

This is different from main clauses, where Norwegian often uses verb-second word order.

Compare:

• Main clause: Vi hørte samklangen.
• Subordinate clause: ... at vi hørte samklangen.

So at hørte vi would be wrong here.

Samklangen is the definite form of samklang.

• samklang = harmony, consonance, blend of sounds
• samklangen = the harmony / the blend

In a choir context, it refers to the combined sound when all the voices fit together properly.

Depending on context, English translations could include:

• the harmony
• the blended sound
• the resonance
• the consonance

In this sentence, it most naturally suggests the full musical blend of the choir.

Yes. The original sentence is natural and slightly more formal or literary because it emphasizes the timing. A simpler version would be:

• Vi hørte ikke samklangen før hele koret sang.
• We didn’t hear the harmony until the whole choir sang.

Another possible rewording is:

• Først da hele koret sang, hørte vi samklangen.
• Only when the whole choir sang did we hear the harmony.

All three are correct, but they have slightly different emphasis:

• Det var ikke før ... at ... = strong emphasis on not until
• Vi hørte ikke ... før ... = more straightforward
• Først da ... = also strongly emphatic

Because the sentence presents the two events as part of the same past situation:

• the whole choir sang
• then we heard the harmony

Norwegian often uses the simple past for this kind of narration.

• sang = sang
• hørte = heard

A perfect or pluperfect form would suggest a different relationship between the actions. Here, the sentence is simply saying that the hearing happened only at the point when the whole choir was singing, so the simple past is the natural choice.