
dumpf
muffled
Describes a sound that is deep, muted, and does not sound clear or bright.
Aus der Ferne hörte man ein dumpfes Grollen.
From far away, you could hear a muffled rumbling.
dull / muffled
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muffled
Describes a sound that is deep, muted, and does not sound clear or bright.
Aus der Ferne hörte man ein dumpfes Grollen.
From far away, you could hear a muffled rumbling.

dull
Describes a feeling or pain that is not stabbing or sharp, but rather pressing and vague.
Nach dem Stoß hatte er einen dumpfen Schmerz im Arm.
After the impact, he had a dull pain in his arm.

numb / dull
A state of mental sluggishness, apathy, or an oppressive, heavy feeling.
Die schlechte Nachricht versetzte ihn in eine dumpfe Verzweiflung.
The bad news plunged him into a numb despair.

dull
Describes a color or light that is not bright or clear, but appears matte and without shine.
Die Wände des Kellers waren in einem dumpfen Grau gestrichen.
The walls of the cellar were painted a dull gray.
The exact meaning of 'dumpf' depends strongly on the noun it describes. Pay attention to whether it is a sound, a pain, a feeling, or a color in order to interpret the word correctly.
Ich hörte einen dumpfen Schlag an der Tür.
I heard a muffled thud at the door.
In connection with sounds, 'dumpf' describes a deep, unclear sound. Typical combinations are 'ein dumpfer Knall' (a muffled bang), 'ein dumpfer Ton' (a dull tone), or 'ein dumpfer Aufprall' (a dull impact).
Das Auto prallte mit einem dumpfen Geräusch gegen die Mauer.
The car hit the wall with a muffled sound.
A 'dumpfer Schmerz' (dull pain) is not sharp or stabbing, but rather pressing and hard to localize. Common combinations are 'ein dumpfer Kopfschmerz' (a dull headache) or 'ein dumpfer Druck in der Brust' (a dull pressure in the chest).
Seit gestern habe ich einen dumpfen Schmerz im Rücken.
Since yesterday, I've had a dull pain in my back.
In an emotional or mental context, 'dumpf' describes a state of apathy or an oppressive feeling. For example, people speak of 'dumpfer Apathie' (numb apathy) or a 'dumpfes Gefühl der Leere' (dull feeling of emptiness).
Nach der Enttäuschung fiel er in einen Zustand dumpfer Resignation.
After the disappointment, he fell into a state of dull resignation.
When 'dumpf' describes a color or light, it means that it is not bright or brilliant. Typical phrases are 'dumpfe Farben' (dull colors), 'ein dumpfes Rot' (a dull red), or 'ein dumpfes Licht' (a dull light).
Der Raum war nur von einer dumpfen Lampe beleuchtet.
The room was lit only by a dull lamp.
weak / matte
Matt and dumpf can both describe a color or surface that is not very bright. Matt emphasizes the lack of shine, while dumpf describes an overall muted and not very lively appearance. Matt fits an intentionally shine-free finish, while dumpf may be more appropriate for an overall lifeless impression.

Die alte Wand hat ein dumpfes Blau, das wenig lebendig wirkt.
The old wall has a dull blue that looks rather lifeless.
Die Wand ist in einem matten Blau gestrichen, das nicht glänzt.
The wall is painted a matte blue that does not shine.