diff --git a/src/tuimble/audio.py b/src/tuimble/audio.py
index bb40631..c7d9399 100644
--- a/src/tuimble/audio.py
+++ b/src/tuimble/audio.py
@@ -55,7 +55,7 @@ class AudioPipeline:
         self._input_gain = 1.0
         self._output_gain = 1.0
 
-    def start(self):
+    def start(self) -> None:
         """Open audio streams."""
         import sounddevice as sd
 
@@ -81,7 +81,7 @@ class AudioPipeline:
 
         log.info("audio pipeline started (rate=%d)", self._sample_rate)
 
-    def stop(self):
+    def stop(self) -> None:
         """Close audio streams and drain stale frames."""
         for stream in (self._input_stream, self._output_stream):
             if stream is not None:
@@ -129,7 +129,7 @@ class AudioPipeline:
     def output_gain(self, value: float):
         self._output_gain = max(0.0, min(2.0, value))
 
-    def _capture_callback(self, indata, frames, time_info, status):
+    def _capture_callback(self, indata, frames, time_info, status) -> None:
         """Called by sounddevice when input data is available."""
         if status:
             log.warning("capture status: %s", status)
@@ -142,7 +142,7 @@ class AudioPipeline:
             except queue.Full:
                 pass
 
-    def _playback_callback(self, outdata, frames, time_info, status):
+    def _playback_callback(self, outdata, frames, time_info, status) -> None:
         """Called by sounddevice when output buffer needs data."""
         if status:
             log.warning("playback status: %s", status)
@@ -173,7 +173,7 @@ class AudioPipeline:
         except queue.Empty:
             return None
 
-    def queue_playback(self, pcm_data: bytes):
+    def queue_playback(self, pcm_data: bytes) -> None:
         """Queue raw PCM data for playback (16-bit, mono, 48kHz)."""
         if self._deafened:
             return