diff --git a/app/main.py b/app/main.py
index dc667d3..0d44dfd 100644
--- a/app/main.py
+++ b/app/main.py
@@ -45,7 +45,7 @@ async def lifespan(_app: FastAPI) -> AsyncGenerator[None, None]:
     logger.info("Extraction processor stopped")
 
 
-def create_app():
+def create_app() -> FastAPI:
     """Create and configure the FastAPI application."""
     app = FastAPI(lifespan=lifespan)
 
diff --git a/app/services/playlist.py b/app/services/playlist.py
index 2b702fe..a571a45 100644
--- a/app/services/playlist.py
+++ b/app/services/playlist.py
@@ -63,7 +63,7 @@ class PlaylistService:
         # Fallback to main playlist if no current playlist is set
         return await self.get_main_playlist()
 
-    async def create_playlist(
+    async def create_playlist(  # noqa: PLR0913
         self,
         user_id: int,
         name: str,
@@ -101,7 +101,7 @@ class PlaylistService:
         logger.info("Created playlist '%s' for user %s", name, user_id)
         return playlist
 
-    async def update_playlist(
+    async def update_playlist(  # noqa: PLR0913
         self,
         playlist_id: int,
         user_id: int,
diff --git a/app/services/sound_normalizer.py b/app/services/sound_normalizer.py
index cd4c5f6..e71c8d2 100644
--- a/app/services/sound_normalizer.py
+++ b/app/services/sound_normalizer.py
@@ -1,5 +1,6 @@
 """Sound normalizer service for normalizing audio files using ffmpeg loudnorm."""
 
+import asyncio
 import json
 import os
 import re
@@ -138,7 +139,9 @@ class SoundNormalizerService:
             stream = ffmpeg.output(stream, str(output_path), **output_args)
             stream = ffmpeg.overwrite_output(stream)
 
-            ffmpeg.run(stream, quiet=True, overwrite_output=True)
+            await asyncio.to_thread(
+                ffmpeg.run, stream, quiet=True, overwrite_output=True,
+            )
             logger.info("One-pass normalization completed: %s", output_path)
 
         except Exception:
@@ -176,7 +179,9 @@ class SoundNormalizerService:
 
             # Run first pass and capture output
             try:
-                result = ffmpeg.run(stream, capture_stderr=True, quiet=True)
+                result = await asyncio.to_thread(
+                    ffmpeg.run, stream, capture_stderr=True, quiet=True,
+                )
                 analysis_output = result[1].decode("utf-8")
             except ffmpeg.Error as e:
                 logger.exception(
@@ -256,7 +261,9 @@ class SoundNormalizerService:
             stream = ffmpeg.overwrite_output(stream)
 
             try:
-                ffmpeg.run(stream, quiet=True, overwrite_output=True)
+                await asyncio.to_thread(
+                    ffmpeg.run, stream, quiet=True, overwrite_output=True,
+                )
                 logger.info("Two-pass normalization completed: %s", output_path)
             except ffmpeg.Error as e:
                 logger.exception(