Oigo a la vecina de al lado cuando habla en voz alta.

Both oír and escuchar can mean to hear in English, but they are used a bit differently.

• oír = to hear, to perceive sound
• escuchar = to listen, to pay attention to what you hear

In Oigo a la vecina de al lado..., the idea is that the speaker simply hears the neighbour’s voice/noise. There is no suggestion of actively listening on purpose, so oigo is the most natural choice.

You could say Escucho a la vecina de al lado..., but that would sound more like you are actually listening to her.

That a is the personal a.

In Spanish, when the direct object is a specific person, you usually put a before it.

So:

• Oigo la música = I hear the music
• Oigo a la vecina = I hear the neighbour

Even though in English we do not add anything before the neighbour, Spanish normally does.

Because la vecina refers to a specific neighbour: the neighbour.

• vecina = neighbour / female neighbour
• la vecina = the neighbour / the female neighbour

Here the speaker has a particular person in mind, so the definite article la is used.

Also notice that vecina is feminine. If it were a male neighbour, it would be el vecino.

De al lado means next door, from next door, or the one next door, depending on context.

So la vecina de al lado means:

• the neighbour next door
• literally: the neighbour from the side next door

This is a very common Spanish expression.

For example:

• el bar de al lado = the bar next door
• la casa de al lado = the house next door

Al is the contraction of a + el.

• a + el = al

In the fixed expression de al lado, the al comes from a el lado.

You do not normally need to analyse it too literally when learning it, because de al lado works as a set phrase meaning next door or beside it.

Important: this is not the same kind of a as the personal a in Oigo a la vecina. They just happen to look the same.

Because the subject of habla is la vecina.

The sentence means that the neighbour is the one speaking loudly.

• yo hablo = I speak
• ella habla = she speaks
• ellos hablan = they speak

Since la vecina is singular and corresponds to she, Spanish uses habla.

It means when she speaks loudly.

Spanish often leaves out subject pronouns like ella when the verb form already makes the subject clear. Here, habla is understood as referring back to la vecina.

So the natural reading is:

• Oigo a la vecina de al lado cuando habla en voz alta.
• I hear the neighbour next door when she speaks loudly.

If you wanted to make it extra explicit, you could say:

• Oigo a la vecina de al lado cuando ella habla en voz alta.

But normally ella is unnecessary.

En voz alta is a very common expression meaning:

• out loud
• in a loud voice
• loudly

Spanish often uses a phrase with a noun instead of an adverb where English uses a single adverb.

So:

• hablar en voz alta = to speak loudly / to speak out loud
• leer en voz alta = to read out loud

Altamente does exist, but it does not mean loudly in this context. It usually means something more like highly.

Spanish word order is more flexible than English word order.

The basic order here is still perfectly normal:

• Oigo = I hear
• a la vecina de al lado = the neighbour next door
• cuando habla en voz alta = when she speaks loudly

Starting with the verb is common in Spanish, especially because the subject yo is omitted. Spanish does not need to say yo unless there is special emphasis or contrast.

So:

• Oigo a la vecina... = normal
• Yo oigo a la vecina... = possible, but with more emphasis on I

Because Spanish often drops subject pronouns when the verb ending already shows who the subject is.

Here:

• oigo can only mean I hear

So yo is not needed.

This is one of the biggest differences from English. In English, you must usually say I hear. In Spanish, oigo already includes the idea of I.

Yes. Oír is an irregular verb.

Its yo form in the present is:

• oigo = I hear

Not oo or o or oyo.

Some present-tense forms of oír are:

• oigo = I hear
• oyes = you hear
• oye = he/she hears
• oímos = we hear
• oís = you all hear
• oyen = they hear

So oigo is just the correct first-person singular form you need to memorise.

Yes, if it is already clear who you are talking about.

• La oigo cuando habla en voz alta.
• I hear her when she speaks loudly.

Here la replaces a la vecina because she is the direct object and feminine singular.

But if the listener does not already know who la refers to, using the full noun phrase a la vecina de al lado is clearer.

Yes.

• la vecina de al lado = the neighbour next door
• la vecina de al lado mío = the neighbour next to me / the neighbour beside mine

The first one is the standard, simple way to say the neighbour next door.

In many situations, de al lado mío can sound more regional or more informal, and in standard Spanish from Spain, de al lado on its own is usually the best choice here.

Yes, very often cuando in this kind of sentence can be understood as when or whenever, depending on context.

So this sentence could imply:

• I hear the neighbour next door when she speaks loudly or
• I hear the neighbour next door whenever she speaks loudly

Because the whole sentence is in the present tense, it can describe a repeated, habitual situation.

Yes, very naturally.

Spanish often uses the simple present where English might use either the simple present or can.

So these are both reasonable English translations:

• I hear the neighbour next door when she speaks loudly.
• I can hear the neighbour next door when she speaks loudly.

The Spanish sentence itself does not explicitly include a separate word for can, but that idea can be understood from context.