ElevenLabs TTS services: revert to Turbo v2.5 as default model

CHANGELOG.md

@@ -30,6 +30,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Changed the default model for both `ElevenLabsTTSService` and
+  `ElevenLabsHttpTTSService` to `eleven_turbo_v2_5`. The rationale for this
+  change is that the Turbo v2.5 model exhibits the most stable voice quality
+  along with very low latency TTFB; latencies are on par with the Flash v2.5
+  model. Also, the Turbo v2.5 model outputs word/timestamp alignment data with
+  correct spacing.
+
 - The development runners `/connect` and `/start` endpoint now both return
   `dailyRoom` and `dailyToken` in place of the previous `room_url` and `token`.
 

src/pipecat/services/elevenlabs/tts.py

@@ -262,7 +262,7 @@ class ElevenLabsTTSService(AudioContextWordTTSService):
         *,
         api_key: str,
         voice_id: str,
-        model: str = "eleven_flash_v2_5",
+        model: str = "eleven_turbo_v2_5",
         url: str = "wss://api.elevenlabs.io",
         sample_rate: Optional[int] = None,
         params: Optional[InputParams] = None,
@@ -274,7 +274,7 @@ class ElevenLabsTTSService(AudioContextWordTTSService):
         Args:
             api_key: ElevenLabs API key for authentication.
             voice_id: ID of the voice to use for synthesis.
-            model: TTS model to use (e.g., "eleven_flash_v2_5").
+            model: TTS model to use (e.g., "eleven_turbo_v2_5").
             url: WebSocket URL for ElevenLabs TTS API.
             sample_rate: Audio sample rate. If None, uses default.
             params: Additional input parameters for voice customization.
@@ -709,7 +709,7 @@ class ElevenLabsHttpTTSService(WordTTSService):
         api_key: str,
         voice_id: str,
         aiohttp_session: aiohttp.ClientSession,
-        model: str = "eleven_flash_v2_5",
+        model: str = "eleven_turbo_v2_5",
         base_url: str = "https://api.elevenlabs.io",
         sample_rate: Optional[int] = None,
         params: Optional[InputParams] = None,
@@ -721,7 +721,7 @@ class ElevenLabsHttpTTSService(WordTTSService):
             api_key: ElevenLabs API key for authentication.
             voice_id: ID of the voice to use for synthesis.
             aiohttp_session: aiohttp ClientSession for HTTP requests.
-            model: TTS model to use (e.g., "eleven_flash_v2_5").
+            model: TTS model to use (e.g., "eleven_turbo_v2_5").
             base_url: Base URL for ElevenLabs HTTP API.
             sample_rate: Audio sample rate. If None, uses default.
             params: Additional input parameters for voice customization.