Ensaiar melhora a afinação e o ritmo.

Because in this sentence, ensaiar means rehearsing / to rehearse in a general sense. Portuguese often uses the infinitive as the subject of a sentence, just like English can do with Rehearsing improves tuning and rhythm or To rehearse improves tuning and rhythm.

So here:

• Ensaiar = rehearsing / to rehearse
• It functions as the subject of melhora

This is very common in Portuguese:

• Estudar ajuda. = Studying helps.
• Dormir faz bem. = Sleeping is good for you.

Because the subject is the single idea ensaiar. Even though the English meaning may feel broad, grammatically it is treated as one singular subject.

So:

• Ensaiar = singular subject
• melhora = improves / improves something

If the subject were plural, then the verb would change:

• Os ensaios melhoram a afinação e o ritmo. = Rehearsals improve tuning and rhythm.

Here, melhora is the third-person singular form of the verb melhorar.

It can mean:

• improves
• makes better

In this sentence, it means that rehearsing has a positive effect on a afinação and o ritmo.

A useful thing to notice:

• melhorar can be used both intransitively and transitively depending on context.
• Here it is being used transitively: rehearsing improves something.

Examples:

• A prática melhora muito. = Practice improves a lot.
• A prática melhora a técnica. = Practice improves technique.

In Portuguese, abstract nouns are often used with definite articles more often than in English.

So Portuguese naturally says:

• a afinação
• o ritmo

Even where English might simply say:

• tuning
• rhythm

This is very normal and idiomatic in Portuguese. You will often see articles with general concepts, body parts, school subjects, and abstract nouns.

For example:

• Ela estuda o português. = She studies Portuguese.
• A música melhora o humor. = Music improves mood.

Yes. The article is a and the noun is afinação, so together they become:

• a + afinação = a afinação

This is completely normal. It is not a contraction.

You will hear both vowels, though in natural speech they may flow together smoothly.

Compare:

• a amizade
• a atenção
• a atividade

All of these are simply the feminine singular article a plus a noun beginning with a.

Afinação usually refers to tuning or intonation, especially in a musical context.

Depending on context, it can mean:

• being in tune
• the quality of correct pitch
• tuning of an instrument or voice

In this sentence, since ritmo also appears, the context is clearly musical. So afinação is probably referring to musical tuning or pitch accuracy.

Related words:

• afinar = to tune / to bring into tune
• afinado = in tune
• desafinado = out of tune

Because ritmo is a masculine noun in Portuguese, so it takes the masculine article o:

• o ritmo

Grammatical gender in Portuguese does not always match any logical real-world category. It is simply a property of the noun that you need to learn along with the word.

A useful habit is to learn nouns with their article:

• a afinação
• o ritmo
• o ensaio
• a música

It is possible in some contexts to omit articles in Portuguese, but here the most natural and standard phrasing is:

• Ensaiar melhora a afinação e o ritmo.

Without the articles, the sentence sounds less natural to most speakers in standard usage. Portuguese generally prefers the articles here when referring to these general musical qualities.

So for a learner, the best choice is definitely:

• a afinação
• o ritmo

Not exactly. They are related, but not identical.

• ensaiar = to rehearse
  • often used for music, theater, dance, or performance preparation
• praticar = to practice
  • broader and more general

So:

• Ensaiar melhora a afinação e o ritmo. = Rehearsing improves tuning and rhythm.

You could also say:

• Praticar melhora a afinação e o ritmo. = Practicing improves tuning and rhythm.

But ensaiar gives more of the idea of rehearsal, especially in a performance setting.

Because Portuguese does not need an extra subject pronoun here. The subject is already present:

• Ensaiar

That whole infinitive verb is acting as the subject of the sentence.

Portuguese often leaves out subject pronouns when they are unnecessary. In this case, adding one would actually sound wrong because ensaiar itself is the subject.

So the structure is:

• Ensaiar = subject
• melhora = verb
• a afinação e o ritmo = object

The structure is:

• Ensaiar = subject
• melhora = verb
• a afinação e o ritmo = direct object

So it follows a normal Subject + Verb + Object pattern.

More literally:

• Rehearsing improves the tuning and the rhythm

Even though ensaiar is a verb form, here it behaves like a noun-like subject.

A natural Brazilian Portuguese pronunciation would sound approximately like:

• en-sai-AR me-LYO-ra a a-fi-na-SAW e u HIHT-mu

A few pronunciation notes:

• ensaiar: stress on the last syllable: -ar
• melhora: the lh sounds like the lli in million for many English speakers
• afinação: the ending -ção sounds like sawng or sown depending on accent, but nasalized
• ritmo: the t is pronounced, but the cluster can feel compact to English speakers

If you want to sound more natural, focus especially on:

• the nasal ending in afinação
• the lh in melhora

Yes, depending on context, a more natural English translation might sometimes be:

• Rehearsing helps improve tuning and rhythm.

That does not change the Portuguese grammar, though. The actual verb in Portuguese is still melhora = improves.

So:

• direct meaning: Rehearsing improves tuning and rhythm
• looser natural English: Rehearsing helps improve tuning and rhythm

Both can communicate the idea well, but melhora itself literally means improves.

Normally, no. You would not usually put o before ensaiar in this sentence.

Here, ensaiar is being used directly as an infinitive subject, which is very natural:

• Ensaiar melhora a afinação e o ritmo.

Adding o before an infinitive can happen in some grammatical discussions or very specific styles, but it is not the normal choice here.

So the standard version is:

• Ensaiar melhora a afinação e o ritmo.

Yes, but the meaning changes slightly.

• Ensaiar melhora a afinação e o ritmo. = Rehearsing improves tuning and rhythm.
• O ensaio melhora a afinação e o ritmo. = The rehearsal improves tuning and rhythm.

The first talks about the activity in general. The second refers to the rehearsal as a thing or event.

So both are grammatical, but they are not exactly the same.

Because a afinação and o ritmo are being treated as general qualities or skills, not as countable items.

Portuguese often uses singular nouns for abstract concepts in this kind of statement:

• a paciência
• o foco
• a coordenação
• o ritmo

So:

• a afinação = tuning / intonation as a general ability
• o ritmo = rhythm as a general skill or quality

Using plurals would suggest multiple specific rhythms or multiple tunings, which is not the intended meaning here.