Cuando escucho esa canción, siento nostalgia por mi ciudad natal.

Here it can mean either when or whenever, depending on how you want to phrase it in English.

Because both verbs are in the present tense, the sentence describes a habitual reaction:

• Cuando escucho esa canción... = When / Whenever I hear that song...

So the idea is not one single occasion, but something that happens repeatedly.

They are both in the present indicative because the sentence talks about a general, repeated situation:

• escucho = I listen / I hear
• siento = I feel

Spanish often uses the present tense this way for habits or regular emotional reactions.

Compare:

• Cuando escucho esa canción, siento nostalgia... = a repeated feeling
• Cuando escuché esa canción, sentí nostalgia... = one specific moment in the past
• Cuando escuche esa canción, sentiré nostalgia... = a future occasion

So the present tense here is completely natural.

Both verbs relate to hearing, but they are not exactly the same.

• escuchar = to listen to, or sometimes to hear in the sense of paying attention to sound
• oír = to hear, in the sense of perceiving sound

In this sentence, escucho esa canción sounds natural because a song is something you typically listen to.

If you said Cuando oigo esa canción..., it would also be understandable, but it suggests more simply when I hear that song rather than actively listening to it.

So:

• escucho esa canción = more like listening to that song
• oigo esa canción = more like hearing that song

No. In Spanish, the subject pronoun is usually left out because the verb ending already shows who the subject is.

• escucho already means I listen / I hear
• siento already means I feel

So Cuando escucho esa canción, siento nostalgia... is the normal way to say it.

You could add yo for emphasis or contrast:

• Yo siento nostalgia, pero ella no.

But in your sentence, leaving it out is the most natural choice.

Spanish has three common demonstratives:

• esta = this
• esa = that
• aquella = that over there / that one further away

In many everyday situations, English that corresponds to esa.

So:

• esa canción = that song

Using esta would make it feel closer to the speaker, as if it were this song here. Using aquella would make it feel more distant, either physically or psychologically.

In a normal sentence like this, esa canción is the most neutral and natural choice.

Sentir nostalgia means to feel nostalgia or to feel a sense of longing for the past / for something or somewhere you miss.

It is a very natural expression in Spanish.

A few related options are:

• siento nostalgia = I feel nostalgia
• estoy nostálgico / nostálgica = I’m feeling nostalgic
• echo de menos... = I miss...

They are similar, but not identical:

• siento nostalgia por mi ciudad natal focuses on the emotional feeling of nostalgia
• echo de menos mi ciudad natal means I miss my hometown

So siento nostalgia is a good choice when you want to express that emotional, reflective feeling.

Both por and de can appear with nostalgia, depending on the expression and the speaker.

In this sentence, sentir nostalgia por mi ciudad natal is a natural way to express longing directed toward your hometown.

You may also hear forms with de, such as:

• sentir nostalgia de mi ciudad natal
• tener nostalgia de mi ciudad natal

So as a learner, the safest point is:

• por is natural here
• de can also be found in Spanish with nostalgia

The exact preference can vary a bit by speaker and context, but your sentence sounds correct and idiomatic.

Mi ciudad natal literally means my native city or my birth city, and in many contexts it works like my hometown in English.

Breakdown:

• mi = my
• ciudad = city
• natal = native / birth-

A small nuance:

• ciudad natal is literally birth city / native city
• English hometown can sometimes mean the place where you grew up, even if you were not born there

So mi ciudad natal is often a good translation of my hometown, but it is slightly more literal.

Because in Spanish, adjectives usually come after the noun.

So:

• ciudad natal = literally city native, but naturally native city / hometown

This is the normal order in Spanish. In fact, ciudad natal is a very common fixed phrase.

If you put natal before the noun, it would sound very unnatural here.

Because Spanish often uses abstract nouns like emotions and states without an article after verbs such as sentir.

So:

• siento nostalgia = I feel nostalgia

That is the normal, natural form.

If you add an article, it changes the feel:

• Siento una nostalgia profunda = I feel a deep nostalgia

That works because the noun is being modified more specifically. But on its own, siento nostalgia is the standard phrasing.

Because Spanish usually does not use a definite article before a noun that already has a possessive adjective like mi, tu, su, etc.

So:

• mi ciudad natal = my hometown
• not la mi ciudad natal

In modern standard Spanish, the possessive already does the job, so no article is needed.

Because the sentence begins with a subordinate clause:

• Cuando escucho esa canción

and then moves to the main clause:

• siento nostalgia por mi ciudad natal

In Spanish, when a clause like this comes first, it is normal to separate it from the main clause with a comma.

So the comma helps show the structure:

• Cuando escucho esa canción,
  siento nostalgia por mi ciudad natal.

You would normally change both verbs to the past:

• Cuando escuché esa canción, sentí nostalgia por mi ciudad natal.

That means:

• When I heard that song, I felt nostalgia for my hometown.

So the difference is:

• escucho / siento = repeated or habitual
• escuché / sentí = one completed moment in the past

This is a very important contrast in Spanish.

In most of Spain, ci is pronounced with the th sound of English think.

So ciudad begins roughly like:

• thyoo-

And the full word is approximately:

• thyoo-DAD

A few details:

• ciu = a single syllable glide, not three separate English-style sounds
• the d between vowels is softer than a strong English d

Also in this sentence:

• canción starts with a k sound, because c before a is pronounced k
• escucho has ch as in church

So in Spain, the sentence sounds different from many Latin American accents mainly because of that ci in ciudad.