Learn Hardcore Portuguese (Portugal): A qualidade do som melhora quando reduzimos a quantidade de ruído. - The sound quality improves when we reduce the amount of noise.

It’s the contraction of de + o = do, meaning of the. So a qualidade do som = the quality of the sound. Portuguese always writes these contractions.

Why is the present tense (melhora, reduzimos) used after quando?

Because the sentence states a general truth/habit. In Portuguese, the present indicative works for timeless facts. For a specific future time, you’d use the future subjunctive: Quando reduzirmos o ruído, a qualidade do som vai melhorar.

Where is the subject nós? Why is it omitted?

Portuguese is a null-subject language: the verb ending -mos in reduzimos already tells you it’s we. You can add nós for emphasis, but it’s not needed: (Nós) reduzimos.

Is reduzir irregular? How is it conjugated here?

Yes, it’s irregular in the present. Key forms:

eu reduzo
tu reduzes
ele/ela/você reduz
nós reduzimos
eles/elas/vocês reduzem

Could I say quando reduzirmos instead of quando reduzimos?

Yes, but the meaning shifts:

quando reduzimos = whenever we reduce (habit/general truth).
quando reduzirmos = when we reduce (in the future, specific occasion). Often paired with a future or periphrastic future in the main clause.

Why say a quantidade de ruído? Can I just say o ruído or menos ruído?

All are fine; nuance differs:

reduzimos a quantidade de ruído = slightly more technical/formal.
reduzimos o ruído = simpler and very common.
há menos ruído = focuses on the resulting state (less noise). Choose what fits your style and context.

What’s the difference between ruído and barulho?

ruído: more technical/neutral; “noise” in audio engineering, signal processing, electronics.
barulho: everyday “noise/ruckus,” less technical. In an audio-quality sentence, ruído is the natural choice.

Why use the definite article in a qualidade do som? Could I say qualidade de som?

In European Portuguese, definite articles are common with abstract/specified nouns. a qualidade do som is the standard phrasing. qualidade de som exists (often in advertising/headlines) but sounds less natural in a full sentence like this.

Could I use fica melhor instead of melhora?

Yes. A qualidade do som fica melhor… = “becomes better,” a bit more colloquial. melhora is neutral and concise. You could also say A qualidade do som melhora quando se reduz o ruído (impersonal).

Should there be a comma before quando?

No comma when the main clause comes first: A qualidade do som melhora quando… If the quando-clause comes first, use a comma: Quando reduzimos…, a qualidade do som melhora.

Can I use se instead of quando?

Yes, with a slight nuance:

quando = whenever/when (temporal, also causal here).
se = if (conditional): A qualidade do som melhora se reduzirmos o ruído. That uses the future subjunctive reduzirmos for a future condition.

Is ruído countable? When would I use the plural ruídos?

As background/technical noise, it’s usually uncountable: ruído. Use ruídos for distinct noises/events: Ouvi vários ruídos estranhos (I heard several strange noises).

Any European Portuguese pronunciation tips for these words?

qualidade: stress on -da- (qua-li-DA-de). Final -de has a very reduced vowel in EP (sounds like “dih”).
som: nasal vowel (like “sohn”; don’t pronounce the final “m”).
ruído: three syllables ru-Í-do; the í is stressed and separate (roo-EE-do). Initial r is a throaty sound in EP (like a French/Parisian “r”).
do: sounds like “du”.

Why is it de ruído and not do ruído after quantidade?

With quantity nouns, Portuguese usually uses bare de for uncountable/generic complements: a quantidade de ruído. Use do/da if it’s a specific, previously identified noise: a quantidade do ruído de fundo da sala.

How could I avoid specifying we and make it impersonal?

Use impersonal se: A qualidade do som melhora quando se reduz o ruído. This is very idiomatic in EP for general statements.

Could I use other verbs like diminuir or baixar?

diminuir is a near-synonym of reduzir here: quando diminuímos o ruído.
baixar is common for levels (volume, settings): baixar o ruído is understandable but a bit less technical; for audio quality, reduzir/diminuir are safest.

Can I say qualidade do áudio instead of qualidade do som?

Yes. áudio is frequent in tech/media contexts: A qualidade do áudio melhora… som is broader and works everywhere; áudio can feel more “device/recording”-oriented.

Are there EU–Brazil differences I should know here?

Grammar is the same. In Brazil you might hear a gente reduz instead of nós reduzimos.
Pronunciation differs (notably the initial r, vowel reduction, and final -de), but the sentence itself is standard in both varieties.