Learn Hardcore Russian: Тихая музыка звучит в кафе как фон. - Quiet music sounds in the cafe as background.

Other forms like тихой are used in other cases (genitive, dative, instrumental, prepositional) or after some prepositions, but not for a simple subject in the nominative here.

Тихо is an adverb (“quietly”), not an adjective, so it can’t directly modify музыка; it would modify the verb:

Музыка звучит тихо. – The music sounds quiet(ly).

Why is it музыка and not музыку?

Музыка here is the grammatical subject of the sentence, so it must be in the nominative case.

Тихая музыка – subject (nominative)
звучит – verb (3rd person singular)
в кафе как фон – adverbial part (where and how)

The verb звучать (to sound) is intransitive in this sentence: it does not take a direct object. So we do not put музыка into the accusative (музыку); that would only happen if it were a direct object of some verb.

Compare:

Я слышу музыку. – I hear music. (Here музыку is the direct object, so accusative.)
Музыка звучит. – The music is sounding. (Here музыка is the subject, so nominative.)

What does звучит mean exactly? Why use звучать and not играть?

Звучит is the 3rd person singular present form of звучать:

звучать – to sound, to be heard

It is used to talk about sounds that exist / are being heard, often in a neutral or descriptive way.

In English you might paraphrase this sentence as:

Soft/quiet music is sounding in the café as a background.

You could also say in Russian:

В кафе играет тихая музыка. – Quiet music is playing in the café.

Играть (to play) focuses more on the action of playing (by musicians, by a device, etc.), while звучать is more about the sound simply existing, being audible. For background music, звучать is very common and sounds natural and descriptive.

What tense and aspect is звучит, and how would I say this in the past or future?

Звучит is:

present tense
3rd person singular
imperfective aspect
of the verb звучать (imperfective)

Imperfective aspect describes an ongoing, repeated, or process-like action/state.

Other forms you might want:

Past:
- Тихая музыка звучала в кафе как фон. – Quiet music was sounding in the café as background.
Future (simple future with imperfective usually expresses a repeated / regular future):
- Тихая музыка будет звучать в кафе как фон. – Quiet music will be sounding in the café as background.

The perfective counterpart is прозвучать (to sound once / to have sounded), which would usually focus on the fact that it sounded at some point or finished sounding:

Музыка прозвучала и смолкла. – The music sounded and then stopped.

What is going on with в кафе? What case is that, and why does кафе not change?

Кафе is an indeclinable noun: its form does not change for case or number. It is grammatically neuter.

In в кафе, the preposition в (in) + a location normally requires the prepositional case. But for кафе, the prepositional form looks exactly the same as the nominative:

nominative: кафе
prepositional: (в) кафе

So syntactically it’s prepositional case, but morphologically the word doesn’t change.

Also note:

в кафе can mean in the café (location, prepositional)
в кафе can also mean into the café (direction, accusative)

Because кафе has the same form in these two cases, you tell the difference from context:

Мы сидим в кафе. – We are sitting in the café. (location)
Мы заходим в кафе. – We are going into the café. (direction)

In your sentence, it’s clearly location: the music is sounding in the café.

What exactly does как do in как фон? Is it “like” or “as”?

In this context как means something between English as and like, introducing a role or function:

как фон ≈ as background, as a background sound

You see this pattern frequently:

работать как учитель – to work as a teacher
использовать как пример – to use as an example

Here, тихая музыка is functioning как фон – as background, not as the main focus of attention. So как marks the function/role of the music.

Why is it как фон and not как фоном? What case is фон here?

After как in the sense of as, Russian normally uses the nominative (which in singular masculine looks the same as the accusative):

как фон – literally “as background”

So фон is in the nominative form.

If you drop как and just say:

Музыка звучит фоном.

then фоном is instrumental case (чем? – by/with/as what?). This also means The music is in the background / functions as background.

Nuance:

как фон – often slightly more “descriptive/comparative”: as background (rather than foreground).
фоном – a very standard instrumental predicate, often used adverbially: in the background, as background.

Both are understandable. …звучит в кафе фоном would sound a bit more idiomatic to many speakers than …как фон, but как фон is also acceptable and clear.

Is the word order fixed? Can I say В кафе звучит тихая музыка как фон or something else?

Russian word order is quite flexible, especially for elements like subject, verb, and place. The basic sentence is:

Тихая музыка звучит в кафе как фон.

Variants and their typical emphasis:

В кафе звучит тихая музыка как фон.
– Fronting в кафе emphasizes the place: In the café, quiet music is sounding as background.
В кафе тихая музыка звучит как фон.
– Slightly marked, focusing more on тихая музыка as something specific at that place.
В кафе звучит тихая музыка.
– Drops как фон, neutral: Quiet music is playing/sounding in the café.
Тихая музыка в кафе звучит как фон.
– Brings в кафе closer to музыка, could sound like you are contrasting this café with some other place.

All of these are grammatically possible; the differences are mainly in information structure and what you want to emphasize. The original order is neutral and clear.

What’s the difference between тихая музыка звучит and музыка звучит тихо?

They are close in meaning but focus on different things.

Тихая музыка звучит…
– тихая is an adjective describing a constant property of the music: It is quiet music (as a type/kind).
Музыка звучит тихо…
– тихо is an adverb describing how it is sounding right now: The music is sounding quietly.

In practice:

тихая музыка suggests that the music itself is of a quiet, gentle nature.
звучит тихо could imply that even loud music happens to be at a low volume at the moment.

Both are correct; your sentence chooses to treat “quiet” as an inherent quality of the music.

How would I say “There is quiet music in the café as background” in a more “existential” way?

Russian often uses a “location + noun” structure instead of an explicit “there is”.

A common option:

В кафе тихая музыка, она звучит как фон.
– There is quiet music in the café; it is sounding as background.

Or shorter, still natural and close to your original:

В кафе звучит тихая музыка как фон.
– Quiet music is sounding in the café as background.

Russian doesn’t need a separate verb “to be” for there is in the present tense; В кафе тихая музыка. by itself already means There is quiet music in the café.

How do you pronounce this sentence, and where is the stress?

Stresses (marked by capital letters) and a simple transcription:

ТИхая МУзыка звуЧИТ в кафе́ как ФОН.

More precisely:

ти́хая – [TEE-ha-ya] (stress on ТИ)
му́зыка – [MOO-zih-ka] (stress on МУ)
звучит – [zvuh-CHEET] (stress on ЧИТ)
в кафе́ – [fkah-FEH] (stress on фе́; в and к cluster, the в is devoiced and almost merges with к)
как – [kak] (short, with a hard k and a)
фон – [fon] (like fone with a short o)

So spoken smoothly:

ТИхая МУзыка звуЧИТ в кафе́ как ФОН.