improvement(chat-voice): modernize ElevenLabs TTS to Flash v2.5 (#4943)

* improvement(chat-voice): modernize ElevenLabs TTS to Flash v2.5

- Switch default TTS model from eleven_turbo_v2_5 to eleven_flash_v2_5 (ElevenLabs recommends Flash over Turbo in all cases; ~75ms latency)
- Drop deprecated optimize_streaming_latency knob plus legacy use_pvc_as_ivc / enable_ssml_parsing flags
- Move output_format to the query string and raise it from mp3_22050_32 to mp3_44100_128 for higher audio quality
- Switch apply_text_normalization from off to auto for correct number/date pronunciation

* improvement(chat-voice): default to Jessica voice (Flash v2.5-optimized)

Replace the legacy Sarah default (EXAVITQu4vr4xnSDxMaL), which has no high-quality
eleven_flash_v2_5 base, with Jessica (cgSgspJ2msm6clMCkdW9) — a current premade
conversational voice verified against the live account and optimized for Flash v2.5.

apps/sim/app/api/proxy/tts/stream/route.ts

@@ -92,7 +92,8 @@ export const POST = withRouteHandler(async (request: NextRequest) => {
       return new Response('ElevenLabs service not configured', { status: 503 })
     }
 
-    const endpoint = `https://api.elevenlabs.io/v1/text-to-speech/${voiceId}/stream`
+    const query = new URLSearchParams({ output_format: 'mp3_44100_128' })
+    const endpoint = `https://api.elevenlabs.io/v1/text-to-speech/${voiceId}/stream?${query.toString()}`
 
     const response = await fetch(endpoint, {
       method: 'POST',
@@ -104,17 +105,13 @@ export const POST = withRouteHandler(async (request: NextRequest) => {
       body: JSON.stringify({
         text,
         model_id: modelId,
-        optimize_streaming_latency: 4,
-        output_format: 'mp3_22050_32', // Fastest format
         voice_settings: {
           stability: 0.5,
           similarity_boost: 0.8,
           style: 0.0,
           use_speaker_boost: false,
         },
-        enable_ssml_parsing: false,
-        apply_text_normalization: 'off',
-        use_pvc_as_ivc: false,
+        apply_text_normalization: 'auto',
       }),
     })
 

apps/sim/app/chat/[identifier]/chat.tsx

@@ -44,7 +44,7 @@ interface ChatRequestPayload {
 }
 
 const DEFAULT_VOICE_SETTINGS = {
-  voiceId: 'EXAVITQu4vr4xnSDxMaL', // Default ElevenLabs voice (Bella)
+  voiceId: 'cgSgspJ2msm6clMCkdW9', // Default ElevenLabs voice (Jessica) — Flash v2.5-optimized
 }
 
 /**

apps/sim/app/chat/hooks/use-audio-streaming.ts

@@ -79,7 +79,7 @@ export function useAudioStreaming(sharedAudioContextRef?: RefObject<AudioContext
     const { text, options } = item
     const {
       voiceId,
-      modelId = 'eleven_turbo_v2_5',
+      modelId = 'eleven_flash_v2_5',
       chatId,
       onAudioStart,
       onAudioEnd,

apps/sim/lib/api/contracts/media/tts-stream.ts

@@ -5,7 +5,7 @@ export const ttsStreamBodySchema = z
   .object({
     text: z.string().min(1),
     voiceId: z.string().min(1),
-    modelId: z.string().optional().default('eleven_turbo_v2_5'),
+    modelId: z.string().optional().default('eleven_flash_v2_5'),
     chatId: z.string().min(1),
   })
   .passthrough()