I played the game in german too and did not notice bad audio (i still use my old Soundblaster Titanium).

Could be the sound settings are borked, a windows codec has wrong settings (i had crashes and issues when i loaded the computerbase coded pack and deinstalled it therefore and use simply the windows standard).

Also ensure the right sound source is enabled and the output meets your setup.

Beynd that and veryfying the games files i have no additional clue.

I don't that this is the reason because the audio from the core game is ok.

German voices do not work for me at all with Phantom Liberty content parts (e.g Songbird dialogs are muted). BTW, there is no localized sound file in the new EP1 folder, so all dialogs of the new contents are muted.
Nevertheless, if no localizations are available, I would expect at least an English dialog fallback. But just giving no sound is an absolutely NO-GO.

When I switch to English, it works fine. So it ended up for me with uninstalling the game...

I wanted to try an offline installation starting at v1.63 but the server seems to be down.
So, that's it for now.

Yes, I can confirm that German Audio in Phantom Liberty sounds comparably worse. It's VERY easy for me to distinguish between Cyberpunk 2077 base game lines and Phantom Liberty lines, because the latter were obviously recorded in a different way (different Studio, different equipment, different settings, whatever...).

I'm glad that someone else also noticed this.
But honestly I wouldn't expect them to change anything about this. They probably don't even care.

Patch 2.02 was released today and the changelog contains this line:

Remastered the voiceover to improve audio quality in German, Simplified Chinese and Japanese.

Maybe they finally noticed the problems after all and fixed it. Can't check it myself right now.

Since the last patch the German voices sound better.