tā shuōhuà de shēngyīn hěn xiǎo, wǒ tīng bú tài qīngchu.

Here 的 links the phrase 说话 (to speak / speaking) to the noun 声音 (sound / voice).

So 他说话的声音 literally means the sound of him speaking or more naturally his speaking voice.

It is a way to turn 说话 into something that describes 声音.

• 他说话的声音很小 = The sound of his speaking is very soft/quiet
• Natural English: He speaks very softly or His voice is very quiet when he speaks

In everyday speech, Chinese sometimes drops 的 in this kind of phrase:

• 他说话声音很小 This is also very common.

Not always. In Chinese, when an adjective acts as the predicate, it often needs something before it, and 很 is the most common choice.

So:

• 声音小 can sound a bit abrupt or contrastive by itself
• 声音很小 sounds more natural as a plain statement

Here 很 may mean very, but often it is just a natural marker and does not need to be translated strongly.

So 很小 here can be understood as:

• very quiet/soft, or simply
• quiet/soft

The exact strength depends on context.

Chinese commonly uses 大 (big) and 小 (small) to talk about volume.

• 声音大 = loud
• 声音小 = quiet / soft

So although 小 literally means small, in this context it refers to the volume of the voice.

This is very natural in Chinese:

• 请小声一点。 = Please speak a little more quietly.
• 他说话声音很大。 = He speaks very loudly.

声音 is the most general and common word for sound or voice.

In this sentence, 声音 works well because it refers to the sound produced when he speaks.

Some related words:

• 声音 = sound / voice
• 嗓音 = voice quality, more specifically the voice itself, often a bit more descriptive
• 声 = a measure word or shorter form in some expressions, not usually used alone here

For this sentence, 声音 is the most normal choice.

This is a very common Chinese pattern:

verb + 不太 + complement

Here:

• 听 = hear / listen
• 清楚 = clear / clearly
• 听清楚 = hear clearly / hear distinctly
• 听不清楚 = cannot hear clearly
• 听不太清楚 = cannot hear very clearly / cannot hear too clearly / cannot hear that clearly

So 清楚 acts like a result or degree complement after 听.

This pattern is very common:

• 看清楚 = see clearly
• 看不清楚 = can’t see clearly
• 说不清楚 = can’t explain clearly

Because in Chinese, the negative element often goes between the main verb and its complement.

So the basic structure is:

• 听清楚 = hear clearly
• 听不清楚 = not hear clearly
• 听不太清楚 = not hear very clearly

If you say 不太听清楚, it sounds much less natural in this sentence.

A helpful way to think about it:

• 听 = the action
• 清楚 = the result/quality of that action
• 不太 goes inside that verb-complement structure

不太 softens the statement.

Compare:

• 听不清楚 = can’t hear clearly
• 听不太清楚 = can’t hear very clearly / can’t hear that clearly

So 不太 often makes the sentence sound less absolute and a bit more polite or moderate.

It suggests:

• not completely impossible
• but still not clear enough

This is very common in spoken Chinese.

This is due to a tone change rule.

Normally, 不 is fourth tone: bù.

But when 不 comes before another fourth-tone syllable, it changes to second tone: bú.

Since 太 is fourth tone (tài), we get:

• 不太 → bú tài

Other examples:

• 不是 → bú shì
• 不要 → bú yào

This is only a pronunciation change; the character is still 不.

Yes. 他说话很小声 is very natural in spoken Chinese.

Compare:

• 他说话的声音很小
• 他说话声音很小
• 他说话很小声

All can mean roughly He speaks very softly / quietly.

Differences:

• 他说话的声音很小 sounds a bit fuller and more explicit
• 他说话声音很小 is common and slightly more compact
• 他说话很小声 is very colloquial and conversational

So learners should understand all of them.

Chinese often places cause and result next to each other without explicitly saying so.

Here:

• 他说话的声音很小 = cause
• 我听不太清楚 = result

Together:

• His voice is very soft, so I can’t hear very clearly.

Adding 所以 is also possible:

• 他说话的声音很小，所以我听不太清楚。

But leaving it out sounds perfectly natural and is very common.

Yes. The verb 听 can cover both ideas depending on context.

In this sentence, it is closer to hear:

• 我听不太清楚 = I can’t hear very clearly

That is because the focus is on whether the sound reaches the speaker clearly, not on the act of intentionally listening.

So although 听 can mean listen, the natural English translation here is hear.

In traditional English grammar terms, the best translation is adverbial: clearly.

But in Chinese grammar, 清楚 is often treated as an adjective that can function as a complement after a verb.

So:

• 清楚 by itself = clear
• 听清楚 = hear clearly
• 看清楚 = see clearly

This is a normal Chinese pattern, where an adjective-like word comes after a verb to describe the result or quality of the action.

Yes, and it is grammatical.

• 他的声音很小，我听不太清楚。 = His voice is very soft, so I can’t hear very clearly.

But there is a slight nuance difference:

• 他的声音很小 focuses on his voice in general
• 他说话的声音很小 specifically focuses on the sound when he speaks

In many contexts, the two are close in meaning, but 说话的声音 is a little more specific.