Je parle à voix basse afin de ne pas déranger mes voisins.

À voix basse is a fixed French expression meaning in a low voice or quietly.

French often uses à in set adverbial expressions of manner:

• à voix haute = out loud
• à voix basse = in a low voice

You may also hear d’une voix basse, but that is less common and sounds more descriptive. In everyday French, parler à voix basse is the natural expression.

Voix means voice. In this sentence, it refers to the way the person is speaking.

A useful thing to remember:

• la voix = the voice
• la voie = the way/path/route

They sound the same, so learners often confuse them in writing.

Because voix is a feminine noun: la voix.

Adjectives usually agree with the noun they describe, so:

• masculine: bas
• feminine: basse

So we get:

• un ton bas sometimes in other contexts
• but une voix basse

That is why the sentence uses à voix basse.

Yes, pour would also work:

• Je parle à voix basse pour ne pas déranger mes voisins.

Both mean in order not to disturb my neighbors.

The difference is mostly register:

• pour = more common and neutral
• afin de = a bit more formal or literary

So afin de is perfectly correct, but pour is more frequent in everyday speech.

In French, negation around an infinitive is usually built as:

ne pas + infinitive

So:

• ne pas déranger = not to disturb
• ne pas parler = not to speak
• ne pas oublier = not to forget

That is why pas does not come directly after de by itself. The full structure is de + ne pas + infinitive.

Because after afin de, French normally uses an infinitive when the subject stays the same.

Here, the subject of both actions is je:

• Je parle...
• Je ne veux pas déranger...

Since the same person is doing both actions, French uses:

• afin de + infinitive

So:

• afin de ne pas déranger

If the subject changed, French would normally use afin que + subjunctive instead.

Example:

• Je parle à voix basse afin que mes voisins ne soient pas dérangés.

Yes.

Use afin de + infinitive when the subject is the same:

• Je parle à voix basse afin de ne pas déranger mes voisins.

Use afin que + subjunctive when there is a different subject or when you need a full clause:

• Je parle à voix basse afin que mes voisins puissent dormir.

So the basic contrast is:

• same subject → afin de
• different subject / full clause → afin que

Because à voix basse is an idiomatic expression. In this fixed phrase, French does not use an article.

Compare:

• à voix basse = in a low voice
• à voix haute = out loud

This is just something to learn as a chunk. Saying à la voix basse would sound unnatural here.

Because déranger is a direct transitive verb. It takes a direct object without a preposition.

So:

• déranger quelqu’un = to disturb someone
• Je dérange mes voisins = I disturb my neighbors

French does not say déranger de quelqu’un in this meaning.

Not always. Déranger is very common, but English disturb can match different French verbs depending on context.

Examples:

• déranger = disturb, bother, inconvenience
• perturber = disturb in a more abstract sense, disrupt
• troubler = disturb emotionally, unsettle

In your sentence, déranger is exactly the natural everyday verb because it means bothering the neighbors with noise.

A very natural spoken version would be:

Je parle à voix basse pour ne pas déranger mes voisins.

That is probably what many speakers would say in conversation.

Other natural possibilities include:

• Je parle doucement pour ne pas déranger mes voisins.
• Je parle tout bas pour ne pas déranger mes voisins.

All are correct, but they are slightly different in tone:

• à voix basse = standard, clear expression
• doucement = softly/gently
• tout bas = very quietly, often more conversational

A careful pronunciation would be roughly:

zhuh parl ah vwah bass ah-fan duh nuh pah day-ron-zhay may vwah-zan

A few useful pronunciation points:

• Je sounds like zhuh
• parle ends with a soft l sound
• voix sounds like vwah
• basse sounds like bass
• afin de is often pronounced smoothly together
• voisins sounds like vwah-zan

There is normally no strong liaison after pas in ne pas déranger.

Not in the same way.

• parler = to speak
• dire = to say, to tell

This sentence is about the manner of speaking, so parler is the right verb:

• Je parle à voix basse...

Using dire would need an object, such as what is being said:

• Je le dis à voix basse. = I say it in a low voice.

So parler fits better because the sentence focuses on speaking quietly, not on a specific thing being said.