Bug Description

Ran into this on 1.4.1 — had speed set to a value outside the valid range and spent some time figuring out why the voice failed. I found it pretty quickly since voice settings was the only thing I'd changed, but without that context it would've been a pain. The plugin doesn't validate or warn on any of the VoiceSettings parameters, so out-of-range values just get sent straight to the 11labs API which silently clamps them. No warning, no error, nothing in the logs — would be nice to improve the experience for future devs.

The Cartesia plugin already does this — _check_generation_config() logs warnings with extra={} for out-of-range speed/volume. The ElevenLabs plugin should do the same.

Expected Behavior

A logger.warning when VoiceSettings params are outside their valid ranges:

• stability: 0.0 - 1.0
• similarity_boost: 0.0 - 1.0
• style: 0.0 - 1.0
• speed: 0.7 - 1.2

Should be warnings not exceptions — 11labs could change the ranges, but at least devs would have something in the logs to go on.

Reproduction Steps

1. Set up ElevenLabs TTS with an out-of-range speed:

   from livekit.plugins.elevenlabs import TTS, VoiceSettings
   
   tts = TTS(
       voice_settings=VoiceSettings(
           stability=0.5,
           similarity_boost=0.5,
           speed=0.5,  # below min of 0.7
       )
   )

2. Synthesize speech — voice failed
3. Check logs — nothing. No warning about the bad speed value
4. Same thing happens through update_options()

Operating System

macOS Sequoia

Models Used

ElevenLabs TTS (eleven_turbo_v2_5)

Package Versions

livekit-plugins-elevenlabs==1.4.1
livekit-agents==1.4.1

Proposed Solution

Add a _validate_voice_settings() function following the Cartesia _check_generation_config() pattern — logger.warning() with extra={} context for each param. Call it from TTS.__init__() and TTS.update_options() when voice_settings is provided.

Happy to put up a PR for this.