Melodia oli tarttuva mutta ei liian yksinkertainen.

Oli is the past tense of olla, which means to be.

So:

• melodia on tarttuva = the melody is catchy
• melodia oli tarttuva = the melody was catchy

In this sentence, oli tells you the statement is about the past.

Finnish does not have articles like the or a/an.

So melodia can mean:

• a melody
• the melody

The exact meaning depends on context. English needs an article, but Finnish usually does not.

Literally, tarttuva comes from the verb tarttua, which means things like:

• to stick
• to catch
• to be contagious

So tarttuva literally means something like catching, contagious, or sticky.

When used about music, it means catchy. That is a very natural use in Finnish, just like in English we say a tune is catchy.

Here tarttuva is being used as an adjective describing melodia.

The subject melodia is singular, and after olla the adjective is normally in the basic nominative singular form:

• Melodia oli tarttuva.
• Laulu oli hyvä.
• Tarina oli kiinnostava.

So tarttuva is simply the normal dictionary-style form used as a predicate adjective after oli.

For the same reason: it is another predicate adjective after an understood oli.

The full sentence could be written out as:

• Melodia oli tarttuva mutta ei ollut liian yksinkertainen.

But Finnish often leaves out repeated words when they are obvious. So instead of repeating oli / ollut, the sentence says:

• Melodia oli tarttuva mutta ei liian yksinkertainen.

That makes yksinkertainen stay in the same basic adjective form.

Because Finnish often omits repeated words when they are easy to understand from context.

So this:

• Melodia oli tarttuva mutta ei liian yksinkertainen.

is a shortened version of something like:

• Melodia oli tarttuva mutta ei ollut liian yksinkertainen.

English sometimes does this too, compare:

• The melody was catchy, but not too simple.

The verb was is understood in the second part.

In the fully expanded version, yes, you would normally have:

• ei ollut = was not

But because the verb is omitted in this shortened structure, only ei remains:

• mutta ei liian yksinkertainen = but not too simple

So this is an example of ellipsis: part of the clause is left out because it is already understood.

Liian means too in the sense of excessively.

So:

• liian yksinkertainen = too simple
• liian vaikea = too difficult
• liian kallis = too expensive

It is an adverb, and here it modifies the adjective yksinkertainen.

This is a very normal Finnish word order:

• Melodia = subject
• oli = verb
• tarttuva = predicate adjective
• mutta = but
• ei liian yksinkertainen = second descriptive part

So the structure is basically:

• Subject + was + adjective + but + not too + adjective

Finnish word order is somewhat flexible, but this version is the most neutral and natural.

Yes. That is completely understandable and grammatically fine.

It is just more explicit:

• Melodia oli tarttuva, mutta se ei ollut liian yksinkertainen.

Compared with the original:

• Melodia oli tarttuva mutta ei liian yksinkertainen.

The original sounds more compact and elegant. Finnish often prefers the shorter version when the meaning is obvious.

Yksinkertainen is a very common Finnish adjective meaning simple. Many Finnish adjectives and nouns end in -nen.

That ending is important because the word changes in a special way in other forms. For example:

• basic form: yksinkertainen
• genitive: yksinkertaisen
• partitive: yksinkertaista

So a learner often notices that -nen words do not keep -nen in all forms.

But in your sentence, it is just in the basic nominative form: yksinkertainen.

It can definitely describe music. That is a normal and natural usage.

For example, tarttuva melodia means:

• a catchy melody
• an ear-catching tune

The same adjective can be used in different contexts:

• tarttuva tauti = contagious disease
• tarttuva nauru = infectious laughter
• tarttuva melodia = catchy melody

So the core idea is something that spreads easily or catches on.

A rough pronunciation guide:

• Melodia ≈ ME-lo-di-a
• oli ≈ O-li
• tarttuva ≈ TART-tu-va
• mutta ≈ MUT-ta
• ei ≈ ey
• liian ≈ LEE-an (two syllables in careful speech: lii-an)
• yksinkertainen ≈ YK-sin-ker-tai-nen

A few useful pronunciation points:

• Stress in Finnish is usually on the first syllable.
• Double consonants matter: tt in mutta and tarttuva is held a little longer.
• Double vowels matter too: ii in liian is longer than a single i.

So the rhythm is strongly first-syllable stressed throughout the sentence.