Röddin hennar hljómar eins og tónlist.

Because -in is the definite article attached to the noun.

• rödd = voice
• röddin = the voice

Icelandic usually adds the to the end of the noun instead of putting a separate word in front, unlike English.

So:

• Röddin hennar = her voice / literally the voice of hers

Hennar means her.

In this sentence, it is the possessive form of hún (she), so it shows ownership:

• hún = she
• hennar = her / hers

So Röddin hennar means her voice.

That is very normal in Icelandic. Possessive words like minn, þinn, hennar, hans, and so on often come after the noun.

So Icelandic commonly says:

• röddin hennar = her voice

rather than putting her first the way English does.

For an English speaker, it may help to think of it as something like:

• the voice her

which sounds wrong in English, but is normal structure in Icelandic.

Usually, röddin hennar is the most natural everyday wording.

A form like hennar rödd can occur, but it tends to sound more emphatic, poetic, or marked. A learner should usually stick with:

• röddin hennar

unless they have a special reason to emphasize her.

Hljómar is the 3rd person singular present tense of the verb hljóma, which means to sound.

So:

• ég hljóma = I sound
• þú hljómar = you sound
• hann / hún / það hljómar = he / she / it sounds

Since röddin hennar is singular, the verb is singular too:

• Röddin hennar hljómar = Her voice sounds

Eins og means like or as.

In this sentence:

• hljómar eins og tónlist = sounds like music

It is a very common expression in Icelandic.

Examples:

• Hann talar eins og kennari. = He speaks like a teacher.
• Það lítur út eins og rigning. = It looks like rain.

Because here music is being used in a general sense, just like in English.

• tónlist = music
• tónlistin = the music

In hljómar eins og tónlist, the meaning is sounds like music in general, not sounds like the music.

So the sentence is saying her voice has a musical quality, not that it sounds like some specific piece of music already being discussed.

Yes, absolutely. It is a natural and idiomatic way to say it.

• eins og = like
• tónlist = music

So:

• eins og tónlist = like music

This sounds very normal in Icelandic.

It is in the nominative singular.

That is because röddin hennar is the subject of the sentence:

• Röddin hennar = the thing doing the verb hljómar

So the structure is:

• [Subject] Röddin hennar
• [Verb] hljómar
• [Comparison] eins og tónlist

Hennar is historically and grammatically a genitive form, and that is why it can express possession.

So in:

• röddin hennar

the idea is basically the voice of her, which English turns into her voice.

This is one reason Icelandic possessive structures can feel different from English ones.

The beginning hlj- is one of those clusters that often feels unusual to English speakers.

A rough guide:

• hlj starts with an h-like breathy sound before the lj sound
• jó sounds roughly like yo
• mar is similar to mar

So hljómar is approximately like HLYO-mar, though that is only a rough English-style guide.

The exact Icelandic pronunciation is something you will get used to by hearing native speakers.

A rough guide is:

• röddin ≈ RER-thin or RÖTH-din, depending on how roughly you approximate it in English

A few important points:

• ö is not the same as English o
• dd here is pronounced with Icelandic ð, a voiced th sound, like in this
• the ending -in is the attached definite article

So it is important not to pronounce it like ordinary English rodd-in.

It is most likely figurative or complimentary.

• Röddin hennar hljómar eins og tónlist.
• Her voice sounds like music.

This is a natural way to praise someone’s voice in Icelandic, just as it is in English. It suggests that her voice is especially beautiful, pleasant, or musical.

Yes, Icelandic word order can be more flexible than English, but the given version is the most straightforward and natural here:

• Röddin hennar hljómar eins og tónlist.

That is the standard neutral order:

• subject
• verb
• comparison phrase

Other orders are possible in special contexts, especially for emphasis, but this is the best pattern for a learner to copy.