So impressive was the performance that ... (C1 Grammar)
For dramatic emphasis, put So + a describing word at the very start, then swap into question order: was / were + the subject, then the rest with that. The strong quality jumps to the front. This is a formal, emphatic move — you meet it in writing, speeches and dramatic retellings, not casual chat. In neutral English you would just say The performance was so impressive that...; reach for the fronted version when you want the quality itself to land first.
Front So + a describing word, then swap the order
The performance was so impressive that the audience applauded. → So impressive was the performance that the audience applauded.
The demand was so high that prices rose. → So high was the demand that prices rose.
Her reply was so sharp that the room fell silent. → So sharp was her reply that the room fell silent.
Not "So impressive the performance was that they applauded." — say "So impressive was the performance that they applauded.". After fronted So impressive, swap to was the performance, not "the performance was".
Try it: The applause was so loud that the speaker paused. Start with So loud and swap the order. (Leave out the words you don't need.) Answer: So loud was the applause that the speaker paused. — After fronted So loud, you swap to question order: was the applause. "The applause was" keeps the normal order, which is exactly the swap you are making, so leave it out. So loud was the applause that the speaker paused.
Such was the ... (when a noun follows)
When a noun follows, front Such and swap: Such + was / were + the + thing, then that + the result. Use Such here, not "So", because a noun comes next. Like So impressive was..., this is a formal, emphatic pattern for writing and dramatic speech; the everyday version is The demand was so great that.... Front Such when you want the sheer scale of the thing to hit first.
The demand was such that production increased. → Such was the demand that production increased.
The shock was such that no one spoke. → Such was the shock that no one spoke.
The damage was such that repairs took months. → Such was the damage that repairs took months.
Not "So was the demand that production increased." — say "Such was the demand that production increased.". A noun follows (the demand), so front Such, not "So".
Try it: The interest was such that tickets sold out. Front Such and swap the order. (Leave out the word you don't need.) Answer: Such was the interest that tickets sold out. — A noun follows (the interest), so you front Such and swap: Such was the interest. "So" goes before a describing word alone, not before a noun, so leave it out. Such was the interest that tickets sold out.
Not until ... did + subject (stress how late it happened)
Put Not until + the time or event at the start to stress that nothing happened before that point — the lateness is the whole point. Then the main clause swaps into question order with a helper: helper + the subject + the verb. With did / does, the helper carries the tense and the main verb goes back to its base verb form (did we realize). With had, the verb keeps its past participle (Not until the trial ended had we realized the truth). This is a formal, emphatic pattern for writing and careful speech; the plain version is We only understood the problem when the results came or We didn't understand it until.... Reach for Not until when you want to spotlight the delay.
We only realized the mistake when the bill arrived. → Not until the bill arrived did we realize the mistake.
She didn't feel safe until the door was locked. → Not until the door was locked did she feel safe.
The truth came out only after the trial ended. → Not until the trial ended did the truth come out.
Not "Not until the results came we understood the problem." — say "Not until the results came did we understand the problem.". The swap (did + we + understand) happens in the main part, not the time part — and the verb drops to its base form, understand, not "understood".
Try it: We understood the problem only when the results came. Start with Not until. The swap happens in the MAIN part, with did. (Leave out the word you don't need.) Answer: Not until the results came did we understand the problem. — After Not until, the swap happens in the main part, not the time part: did we understand. "We understood" keeps the normal order and the past ending, both of which the swap with did changes, so leave it out. Not until the results came did we understand the problem.