🔊 Voice / TTS Architecture

Four-tier text-to-speech fallback chain. Best-quality cloud voices when online; bundled neural models when not. Used by Prism AAC, in-call notifications, accessibility narration, and any app feature that speaks.

🎚️ Four-Tier Fallback Chain

The chain is automatic — no user configuration required. The voice picker (paid) lets users override their default with any Tier 1 voice.

🎤 Voice Cloning (Paid)

“Speak in MY voice — I trained it last week.”

• 3-minute training sample uploaded once via the Voice Picker UI.
• Inworld voice-clone training takes ~10 minutes; the cloned voice is then available alongside the standard 60+ voices.
• Workspace-scoped — clones are bound to the workspace; staff voices auto-shared, patient voices private.
• Use cases: AAC users speak in a parent’s voice; clinicians who prefer to hear notes in their own voice; demo videos for parents/caregivers.

🌍 Subsidized Languages (Free Tier)

Synalux absorbs Inworld TTS-2 cost for these languages on the free tier so users in regions where the platform serves underserved populations get premium voices at no cost:

ro (Romanian) · uk (Ukrainian) · ru (Russian) · de (German) · ko (Korean) · ar (Arabic)

🩺 Why This Matters Clinically

• Children with speech impairments depend on AAC’s TTS for their actual voice — robotic Tier-3 fallbacks aren’t acceptable for daily use; Tier 1 / 1.5 must succeed.
• Bilingual households need accurate prosody in both languages — Tier 1 is critical for non-English.
• Offline reliability — a child at school without Wi-Fi must still have their device speak. Tier 1.5 + 2 + 3 are bundled; the device always talks.

🏗️ Architecture

POST /api/v1/tts                Generate TTS audio (auto tier-route based on lang + tier + connectivity)
POST /api/v1/tts/public         Anonymous TTS for AAC widgets (rate-limited per IP)
GET  /api/v1/tts/voices         List available voices for the user's tier + language
POST /api/v1/voices/clone       Submit a voice-clone training sample (paid)

Routing logic:

synthesize(text, lang, voice?) →
  if voice && Tier1.available(voice): return Tier1.speak(text, voice)
  if Tier1.available(lang) && (paid || Tier1.subsidizes(lang)): return Tier1.speak(text)
  if Tier1_5.supports(lang): return Tier1_5.speak(text)        // Kokoro
  if Tier2.has(lang):        return Tier2.speak(text)          // Web Speech API
  return Tier3.speak(text)                                     // espeak-ng

💳 Plans

See full pricing → 

🔄 Where TTS Is Used

• Prism AAC — picture tiles → speech, keyboard speak button, math panel AI tutor.
• In-call notifications — meeting started, patient joined, recording started.
• Accessibility narration — for users with low vision; reads notifications + form errors.
• AAC chat — assistant responses can be auto-spoken with the user’s selected voice.