project
Realtime TTS-2 - A real-time speech synthesis model launched by Inworld AI
Realtime TTS-2 is a next-generation real-time speech synthesis model from Inworld AI, specifically designed for conversational AI scenarios. The model can convert text into natural speech and, more importantly, 'understand' the audio emotion, tone, and... of the conversational context.
What is Realtime TTS-2?
Realtime TTS-2 is a next-generation real-time speech synthesis model from Inworld AI, specifically designed for conversational AI scenarios. The model can convert text into natural speech and, more importantly, "understand" the audio emotion, tone, and rhythm within the context of a conversation, enabling multi-turn perceptual speech synthesis. Realtime TTS-2 supports cross-language switching of 100+ languages and natural language speech direction control (such as...). , And design virtual sounds directly from text descriptions, with latency as low as real-time streaming.
Main functions of Realtime TTS-2
- Voice Direction: Through natural language descriptions (e.g., "tired but warm, like she just got home") or inline tags (e.g.) , It provides real-time guidance on the emotion, speed, and style of speech, without the need for fixed emotion enumeration.
- Conversational AwarenessThe model receives actual audio (not just text transcription) of the previous rounds of conversation as input and automatically adjusts its response based on the user's tone—the same sentence will be more cheerful after a joke and more somber and cautious after bad news.
- Crosslingual consistencyA single voice identity can remain consistent across 100+ languages, supporting seamless switching between Chinese, English, Spanish, Japanese, and other languages within the same sentence, without the need to manage different voice libraries by language.
- Advanced Voice DesignA custom sound can be generated and saved using a text description (such as "warm low-pitch female with slight rasp, late-30s") without the need for a reference audio.
The technical principles of Realtime TTS-2
- End-to-end unified architectureIt integrates the three stages of "listening-thinking-expressing" into a single persistent connection. Unlike traditional TTS which generates single sentences in isolation, the model is trained within the complete audio context of a multi-turn dialogue, allowing timbre, tone, and emotional state to automatically continue with the dialogue flow.
- Multi-turn audio awareness mechanism (Conversational Awareness)It receives actual audio (not just text transcription) of the previous rounds of conversation as input and automatically adjusts its response based on the user's tone and emotion. The same sentence will produce different voice expressions in different conversational contexts.
- Token-level streaming audio generationSupports SSE (Server-Sent Events) streaming and token-level audio output for low-latency real-time dialogue. Optimized for dialogue scenarios, it meets the real-time interaction needs of voice assistants, game NPCs, and more.
- Voice Direction Control (Natural Language)It guides speech generation through natural language descriptions (such as "tired but warm, like she just got home") and supports inline tags (such as [laugh], [breathe], [sigh]) to adjust emotion, speech rate and style in real time without the need for fixed emotion enumeration.
- Cross-language consistency technologyA single voice identity can remain consistent across 100+ languages, supporting seamless switching between multiple languages within the same sentence, without the need to manage different voice libraries by language.
- Advanced voiceprint designCustom sounds can be generated and saved using only text descriptions, without the need for reference audio, enabling zero-sample voiceprint design. Stability modes are supported (Expressive / Balanced / Stable).
How to use Realtime TTS-2
- Call via Inworld APIAfter registering an Inworld AI account, specify the model identifier as Realtime TTS-2 in the request, and you can generate audio by sending text and voice direction commands via REST or Realtime API.
- Integration with Realtime SessionsIn a Realtime session, the system automatically passes the user's audio history as context, so developers only need to maintain the same session connection and do not need to manually concatenate the prior_audio field.
- Sound cloning and design: Re-clone the sound using the original reference audio to maintain optimal fidelity; or create a new sound directly via text prompt and select a stability mode (Expressive / Balanced / Stable).
Key information and usage requirements for Realtime TTS-2
- Product NameInworld Realtime TTS-2
- PublisherInworld AI
- Product PositioningReal-time dialogue speech synthesis model
- Supported languagesSupports 100+ languages and allows cross-language switching within sentences.
- Latency performanceReal-time streaming, low latency for the first token
- Access method：Inworld API / Inworld Realtime API / Node & Python SDK
- PricingPricing is based on Inworld's official pricing (see inworld.ai/pricing for details).
- compatibility Supports the OpenAI Realtime protocol; existing OpenAI Realtime clients can connect simply by modifying the URL.
The core advantages of Realtime TTS-2
- Context-aware expressionThe AI voice dynamically adjusts its tone based on multi-turn audio context, enabling it to have true conversational coherence rather than being mechanically spliced together from single sentences.
- Director-level voice controlThe natural language prompt allows for fine-tuning of emotions and styles, and supports inline non-verbal markers (sighs, laughter, breathing sounds), making it far more expressive than a fixed emotion slider.
- Cross-language timbre unificationThe same virtual character maintains a completely consistent voice identity in a global multilingual environment, significantly reducing the production cost of multilingual content.
- Low-latency real-time streamingOptimized for dialogue scenarios, it supports SSE streaming to meet the real-time interaction needs of voice assistants, game NPCs, and other applications.
- Zero-sample voiceprint designNo need to collect voice actor audio; text descriptions can generate professional-grade character voices, with extremely low iteration costs.
Realtime TTS-2 project address
- Project official website: https://inworld.ai/blog/realtime-tts-2
Comparison of Realtime TTS-2 with similar competing products
| Comparison Dimensions | Inworld Realtime TTS-2 | ElevenLabs | OpenAI GPT-4o Audio |
|---|---|---|---|
| Voice quality (Artificial Analysis ranking) | #1 | #3 | #5 |
| Natural conversational expression | Unclear | ||
| Real-time low latency | Unclear | Unclear | |
| Conversational Awareness | |||
| Natural Language Speech Direction Control | |||
| Sound cloning | Unclear | ||
| Text description generates sound | |||
| Unified timbre across 100+ languages | |||
| User voice profile perception | |||
| Single customized voice API | |||
| OpenAI Realtime protocol compatible | (Original) |
Application scenarios of Realtime TTS-2
- AI game NPCsThis feature allows game characters to have voices that can sense player emotions and respond in real time, enabling NPCs to change their tone naturally with the context of the conversation, greatly enhancing immersion and the realism of the interaction.
- Intelligent customer service and voice assistantThe system automatically adjusts its response strategy based on the user's tone, using a low and cautious tone when soothing complaints and a light and enthusiastic tone when celebrating successes, thus achieving a truly humanized service experience.
- Multilingual Educational TutoringThe same virtual foreign teacher voice can be seamlessly switched between 100+ languages, including Chinese, English, and Japanese, maintaining learners' familiarity with the voice identity and reducing the cognitive switching costs in multilingual learning.
- Virtual anchors and audio contentGenerate differentiated character voices in batches via text prompts, support emotionally rich long text narration, and quickly produce high-quality audio content without the need for real voice actors.