diff --git a/examples/voice/cli/cli.py b/examples/voice/cli/cli.py
index 5dc53ab..496b072 100644
--- a/examples/voice/cli/cli.py
+++ b/examples/voice/cli/cli.py
@@ -163,9 +163,6 @@ async def main() -> None:
     # Set chunk size
     config.chunk_size = args.chunk_size
 
-    # Set common items
-    config.enable_diarization = True
-
     # Handle config display
     if args.show_compact:
         print(config.to_json(indent=2, exclude_unset=True, exclude_none=True))
diff --git a/sdk/voice/speechmatics/voice/_client.py b/sdk/voice/speechmatics/voice/_client.py
index 978d130..a376eb8 100644
--- a/sdk/voice/speechmatics/voice/_client.py
+++ b/sdk/voice/speechmatics/voice/_client.py
@@ -165,11 +165,11 @@ def __init__(
         # -------------------------------------
 
         # Default to EXTERNAL if no config or preset string provided
-        if config is None and not preset:
+        if config is None and preset is None:
             config = VoiceAgentConfigPreset.EXTERNAL()
 
         # Check for preset
-        elif preset:
+        elif preset is not None:
             preset_config = VoiceAgentConfigPreset.load(preset)
             config = VoiceAgentConfigPreset._merge_configs(preset_config, config)
 
@@ -1085,7 +1085,7 @@ async def _add_speech_fragments(self, message: dict[str, Any], is_final: bool =
                         is_final=is_final,
                         attaches_to=result.get("attaches_to", ""),
                         content=alt.get("content", ""),
-                        speaker=alt.get("speaker", None),
+                        speaker=alt.get("speaker", "UU"),
                         confidence=alt.get("confidence", 1.0),
                         volume=result.get("volume", None),
                         result={"final": is_final, **result},
@@ -1382,8 +1382,7 @@ async def _emit_segments(self, finalize: bool = False) -> None:
                 self._turn_start_time = self._current_view.start_time
 
             # Send updated speaker metrics
-            if self._dz_enabled:
-                self._calculate_speaker_metrics(partial_segments, final_segments)
+            self._calculate_speaker_metrics(partial_segments, final_segments)
 
         # Emit end of turn
         if finalize:
diff --git a/tests/tts/async_http_test.py b/tests/tts/async_http_test.py
index 72b5eff..8fddca2 100644
--- a/tests/tts/async_http_test.py
+++ b/tests/tts/async_http_test.py
@@ -6,7 +6,7 @@
 
 
 @pytest.mark.asyncio
-@pytest.mark.skipif(os.getenv("SPEECHMATICS_API_KEY") is None, reason="Skipping test if API key is not set")   
+@pytest.mark.skipif(os.getenv("SPEECHMATICS_API_KEY") is None, reason="Skipping test if API key is not set")
 async def test_async_http():
     async with AsyncClient() as client:
         async with await client.generate(text="Hello world") as response:
diff --git a/tests/voice/test_15_esl.py b/tests/voice/test_15_esl.py
new file mode 100644
index 0000000..bdb79b5
--- /dev/null
+++ b/tests/voice/test_15_esl.py
@@ -0,0 +1,47 @@
+import asyncio
+import os
+
+import pytest
+from _utils import get_client
+from _utils import log_client_messages
+from _utils import send_audio_file
+
+from speechmatics.voice._presets import VoiceAgentConfigPreset
+
+# Skip for CI testing
+pytestmark = pytest.mark.skipif(os.getenv("CI") == "true", reason="Skipping transcription tests in CI")
+
+# Skip if ESL tests is not enabled
+pytestmark = pytest.mark.skipif(os.getenv("TEST_ESL", "0").lower() not in ["1", "true"], reason="Skipping ESL tests")
+
+# Constants
+API_KEY = os.getenv("SPEECHMATICS_API_KEY")
+URL = os.getenv("TEST_ESL_URL", "ws://localhost:8080/v2")
+SHOW_LOG = os.getenv("SPEECHMATICS_SHOW_LOG", "0").lower() in ["1", "true"]
+
+
+@pytest.mark.asyncio
+async def test_esl():
+    """Local ESL inference."""
+
+    # Client
+    client = await get_client(api_key=API_KEY, url=URL, connect=False, config=VoiceAgentConfigPreset.FAST())
+
+    # Add listeners
+    log_client_messages(client)
+
+    # Connect
+    await client.connect()
+
+    # Check we are connected
+    assert client._is_connected
+
+    # Load the audio file `./assets/audio_01_16kHz.wav`
+    await send_audio_file(client, "./assets/audio_01_16kHz.wav")
+
+    # Wait 5 seconds
+    await asyncio.sleep(5)
+
+    # Close session
+    await client.disconnect()
+    assert not client._is_connected