Mikrofonen gjør stemmen hennes tydeligere, men hun hører nesten ikke scenelysene som suser.

In Norwegian, which possessive you choose depends on who the subject of the clause is.

• sin / sitt / sine = the subject’s own something (reflexive possessive)
• hans / hennes = someone else’s something (non‑reflexive)

In the clause Mikrofonen gjør stemmen hennes tydeligere:

• Subject: Mikrofonen
• Possessor of the voice: a woman (hun), not the microphone

Because the possessor is not the subject, you must use hennes, not sin.

If you wrote Mikrofonen gjør stemmen sin tydeligere, it would literally mean the microphone makes its own voice clearer, which is odd.

Compare:

• Hun gjør stemmen sin tydeligere.
  She makes her (own) voice clearer.
• Hun gjør stemmen hennes tydeligere.
  She makes *another woman’s voice clearer.*

Norwegian allows possessives both after and before the noun:

• stemmen hennes = her voice (neutral, most common)
• hennes stemme = her voice (more emphatic / formal / contrastive)

General tendencies:

• Postposed possessive (noun + possessive)
  
  • stemmen hennes, bilen min, huset vårt
  • This is the most neutral, everyday pattern, especially with hans / hennes.
• Preposed possessive (possessive + noun)
  
  • hennes stemme, min bil, vårt hus
  • Feels more emphatic, contrastive, or stylistically marked (often more written or poetic).

So stemmen hennes is simply the most natural, neutral way to say her voice in this sentence.
Hennes stemme would also be correct, but it would slightly stress her voice as opposed to somebody else’s.

This is a very common pattern in Norwegian:

gjøre + object + adjective (or adjective in comparative)
= to make something (more) + adjective

In the sentence:

• Mikrofonen (subject)
• gjør (verb)
• stemmen hennes (object)
• tydeligere (object complement / predicative adjective)

So literally: The microphone makes her voice clearer.

Other examples:

• Kaffen gjør meg våken. – The coffee makes me awake.
• Sola gjør dagene lengre. – The sun makes the days longer.

You could also say:

• Mikrofonen gjør at stemmen hennes blir tydeligere.

but that is heavier and less direct than gjør stemmen hennes tydeligere.

Both are possible:

• tydeligere = clearer
• mer tydelig = more clear / clearer

Tydelig forms its comparative in two ways:

• tydelig → tydeligere (suffix -ere)
• tydelig → mer tydelig (with mer = more)

General guidelines:

• Short(er) adjectives usually take -ere (and -est(e) in superlative):
  klar → klarere, vakker → vakrere.
• Longer adjectives often use mer / mest:
  interessant → mer interessant.

But many adjectives, like tydelig, allow both, and tydeligere is very common and idiomatic here.

Meaning-wise, tydeligere and mer tydelig are effectively the same in this sentence.

The normal word order is:

Subj – Verb – Adverb(s) – Ikke – Object

Here you have a fixed expression nesten ikke (almost not / hardly), which functions like one unit:

• hun hører nesten ikke scenelysene
  = she almost doesn’t hear / she can hardly hear the stage lights.

If you say:

• hun hører ikke nesten scenelysene

it becomes ungrammatical or at least very odd, as if nesten were trying to modify scenelysene instead of ikke.

So the natural structure is:

• hører [nesten ikke] [scenelysene …]

Yes, nesten ikke corresponds to English almost not or hardly:

• Hun hører nesten ikke scenelysene som suser.
  ≈ She hardly hears the stage lights that are humming.

Nuance:

• ikke = not
• nesten ikke = not quite not, but very close to it → barely / hardly

Other examples:

• Jeg ser nesten ikke noe. – I can hardly see anything.
• Han spiser nesten ikke kjøtt. – He hardly eats any meat.

Scenelysene is a definite plural compound noun.

Breakdown:

• scene = stage
• lys = light (neuter noun)

As a compound:

• scenelys = stage light / stage lighting

Since lys is neuter and keeps the same form in singular and plural, the forms are:

• Indefinite singular: et scenelys – a stage light
• Definite singular: scenelyset – the stage light
• Indefinite plural: scenelys – stage lights
• Definite plural: scenelysene – the stage lights

So scenelysene = the stage lights.

Here som is a relative pronoun, similar to English that/which/who.

• scenelysene som suser = the stage lights that (are) humming

In this relative clause:

• som is the subject of the clause som suser.
• Because som is the subject, you cannot drop it in Norwegian.

Compare:

• Scenelysene som suser er gamle. – The stage lights that hum are old.
• Scenelysene suser. – The stage lights hum. (main clause, no som)

So som is required here; without it, you don’t have a relative clause modifying scenelysene.

Yes, grammatically you can:

• scenelysene som suser
• de susende scenelysene

Both can translate as the humming stage lights, but there is a small nuance:

• som suser = a full relative clause, often felt as a bit more dynamic / event-like (the lights are humming right now).
• susende = a present participle used like an adjective; it sounds slightly more descriptive / literary, like a permanent characteristic.

In everyday language, scenelysene som suser is very natural and clear.
de susende scenelysene is also fine, just a bit more stylistic.

Norwegian distinguishes between:

• å høre = to hear (passively; sound reaches your ears)
• å lytte (til) = to listen (to) (actively, on purpose)

In the sentence:

• Hun hører nesten ikke scenelysene som suser.
  = She can hardly hear the stage lights that are humming.

This is about what she is able to perceive, not about her actively trying to listen to the lights. So høre is the correct verb.

If you said:

• Hun lytter nesten ikke til scenelysene.

it would mean something like she hardly ever listens to the stage lights, implying a deliberate action, which is strange in this context.

Men is a coordinating conjunction meaning but.

Norwegian comma rule:
You put a comma before men, og, for, eller when they join two independent main clauses (each with its own subject and verb).

Here:

1. Mikrofonen gjør stemmen hennes tydeligere
   – main clause (subject + verb + object + complement)
2. hun hører nesten ikke scenelysene som suser
   – another main clause (subject + verb + object)

They are joined by men, so you write:

• Mikrofonen gjør stemmen hennes tydeligere, men hun hører nesten ikke scenelysene som suser.

Yes, that is also grammatical:

• Mikrofonen gjør stemmen hennes tydeligere.
• Mikrofonen gjør at stemmen hennes blir tydeligere.

Both mean essentially the same thing: The microphone makes her voice clearer.

Differences:

• gjør X tydeligere is shorter and more direct. Very natural in spoken and written Norwegian.
• gjør at X blir tydeligere focuses more on cause and effect (literally makes that X becomes clearer). It sounds a bit more explicit or formal.

In everyday style, the original sentence is the most idiomatic.

Tydelig = clear.
Tydeligere = clearer / more clear.

The context implies a comparison: her voice with the microphone vs. without it.

So:

• Mikrofonen gjør stemmen hennes tydeligere
  = The microphone makes her voice clearer (than before).

If you used tydelig:

• Mikrofonen gjør stemmen hennes tydelig.

it would sound like the microphone makes her voice simply clear, rather than clearer, and you lose the sense of improvement.

Not necessarily in a strict grammatical sense, but they normally will in context.

In the sentence:

• … stemmen hennes … men hun hører nesten ikke …

we usually understand:

• hennes = her (some woman)
• hun = she (the same woman, unless context clearly says otherwise)

Grammatically:

• hennes can refer to any female person mentioned in the wider context.
• hun is an independent subject pronoun; it could refer to:
  • the same woman as hennes, or
  • a different woman, if the context makes that clear.

Because there is no other clear female referent introduced, the natural reading is that hun and hennes refer to the same person.