Learn Danish: Lydkvaliteten er desværre knap så imponerende. - The sound quality is unfortunately not quite as impressive.

The phrase knap så means not quite as or less. It softens the negative statement. Saying ikke så imponerende is a harder way of saying not as impressive, whereas knap så implies the sound might still be okay, but it just falls a bit short of expectations.

Why is desværre placed where it is, rather than at the beginning of the sentence?

In a standard main clause, central adverbs like desværre are placed immediately after the finite verb, which here is er. You could put desværre at the very beginning to emphasize the regret, but that would force the subject and verb to swap places due to the V2 rule, resulting in Desværre er lydkvaliteten knap så imponerende.

If we were talking about a neuter noun instead of Lydkvaliteten, would imponerende get a -t at the end?

No, it would not change. The word imponerende is a present participle functioning as an adjective, much like English adjectives ending in -ing. In Danish, adjectives that end in -ende never add a -t for neuter nouns or an -e for plural nouns; they always keep the exact same form.

In the compound noun Lydkvaliteten, does it get its -en ending from lyd or kvalitet?