В этой тональности он попадает в ноты.

It is the prepositional case after в because the phrase means in this key / in this tonality, that is, a setting or context, not motion into something.

• тональность = a feminine noun
• эта тональность = this key / this tonality
• In the prepositional case:
  • эта → этой
  • тональность → тональности

So:

• в этой тональности = in this key

This is similar to:

• в этой комнате = in this room
• в этой песне = in this song

Yes. In this sentence, тональность means the musical key or tonality.

For example, it can refer to something like:

• в до мажоре = in C major
• в этой тональности = in this key

A learner might wonder whether Russian uses ключ for musical key, since English does. Normally, for music, Russian uses тональность, not ключ.

So in this sentence, в этой тональности means something like:

• at this pitch level
• in this key
• when the song is set in this key

Literally, попадать means something like to hit, to land in, to get into, to reach the target.

So попадать в ноты literally feels like:

• to hit the notes
• to land on the notes

Idiomatically, in a musical context, it means:

• to sing the correct notes
• to stay on pitch
• to hit the notes
• to sing in tune

So the phrase is about accuracy of pitch.

This is a very common question, because earlier in the sentence в took the prepositional case (в этой тональности), but here it takes the accusative: в ноты.

That happens because these are two different uses of в:

1. в + prepositional = location or setting

   • в этой тональности = in this key

2. в + accusative = direction, goal, target

   • попадать в ноты = to hit the notes

With попадать / попасть, Russian often treats the object as a target:

• попасть в цель = to hit the target
• попасть в мяч = to hit the ball
• попадать в ноты = to hit the notes

So в ноты uses the accusative because the notes are the target being reached correctly.

Also, ноты is plural and inanimate, so nominative plural and accusative plural look the same:

• nominative: ноты
• accusative: ноты

Попадает is the imperfective present form of попадать.

That usually gives a sense like:

• he hits the notes
• he is hitting the notes
• he manages to hit the notes
• he can hit the notes in this setting

In this sentence, it most naturally sounds like a general present or a comment on what is happening in this key:

• In this key, he hits the notes
• In this key, he can stay on pitch

Compare:

• он попадает в ноты = imperfective, general/process/repeated success
• он попадёт в ноты = perfective future, he will hit the notes
• он попал в ноты = perfective past, he hit the notes

So попадает fits well if the speaker is describing his ability or performance in this key.

Yes, it is a very common musical expression.

It is used for singers, and sometimes more generally for musical performance, to mean:

• to hit the right notes
• to sing on pitch
• not to be off-key

A very common opposite is:

• не попадать в ноты = to miss the notes, to sing off-key

For example:

• Он не попадает в ноты. = He’s not hitting the notes.
• Она хорошо попадает в ноты. = She hits the notes well.

So this is a phrase worth learning as a chunk.

It can suggest either, depending on context.

Without extra context, it often sounds like a present-time observation with a general nuance:

• In this key, he hits the notes
• In this key, he can hit the notes
• In this key, he sings in tune

Russian present tense often covers both:

• what is happening now
• what regularly happens
• what someone is capable of in a given situation

So the sentence may imply that this key suits him, and because of that, he is able to sing the notes correctly.

Russian word order is flexible, so the speaker can move parts of the sentence to emphasize different things.

Starting with в этой тональности highlights the condition or frame:

• in this key is the important setup
• then the speaker says what happens in that setup: он попадает в ноты

This gives a meaning like:

• In this key, he hits the notes
• When it’s in this key, he can stay on pitch

If you changed the word order, the meaning would stay similar, but the emphasis would shift:

• Он в этой тональности попадает в ноты.
  More neutral, with he a bit more prominent.

• Он попадает в ноты в этой тональности.
  The final phrase can sound more like an afterthought or clarification.

So the original word order is natural if the speaker wants to emphasize that the key is the reason.

Yes. Тональность is a more specifically musical way to talk about the key.

The sentence suggests something like:

• when the piece is transposed to this key, he can sing it properly
• this key suits his voice
• in this version, the notes are within his comfortable range

So the sentence is not only about isolated notes. It implies a broader musical setting: the whole song or passage is in a key where he can perform accurately.

Yes. Depending on context, good English translations include:

• In this key, he hits the notes.
• In this key, he sings in tune.
• In this key, he stays on pitch.
• In this key, he can hit the notes.

The most literal natural translation is probably he hits the notes, but if you want to express the musical idea more idiomatically in English, he sings in tune or he stays on pitch can work very well.