One sentence, one main beat
A word has its own fixed stress. A sentence has one more: a single syllable that stands out above all the others, louder, longer and higher. That is the Satzakzent. It belongs to the moment, and you place it fresh every time you speak. A sentence is not a row of equally important words, it is one peak with quieter words around it.
The peak in a neutral sentence
Ich habe gestern einen Film gesehen.
I watched a film yesterday.
Wir fahren morgen nach Berlin.
We're going to Berlin tomorrow.
Ich kann meinen Schlüssel nicht finden.
I can't find my key.
the beat falls before nicht finden, not on it
The closing verb is quiet
German sends a participle or an infinitive to the very end of the clause. The beat falls just before it, and the closing verb is spoken low and quickly. By then the listener has been waiting for it since the auxiliary or the modal, so it is old news. This is also true in a subordinate clause.
Wir haben gestern eine Wohnung gefunden.
We found a flat yesterday.
Ich muss noch schnell zur Post gehen.
I just have to pop to the post office.
Ich glaube, dass sie schon weg ist.
I think she's already gone.
The catch before a vowel
German rhythm sounds choppy to English ears mainly because of one habit. A word that starts with a vowel gets a tiny catch in the throat first, the glottal stop: am | Abend, in | einer | Stunde, völlig | egal. English glides a final consonant straight into the next vowel (an hour sounds like a nour). German keeps two words apart. The catch is not written.
Feel the catch
am Abend
in the evening
not a-mabend: a small catch between the two words
in einer Stunde
in an hour
völlig egal
completely irrelevant