Building Real-Time Voice-Enabled AI Talking NPCs in Unity

Building Real-Time Voice-Enabled AI Talking NPCs in Unity
Introduction
Imagine a game where non-playable characters (NPCs) engage in lifelike conversations, respond to your voice in real time, and express emotions through perfectly synced lip movements. This isn’t science fiction—it’s achievable today with modern AI tools and game engines like Unity.
In this guide, you’ll learn how to create AI-driven NPCs that:

  • Listen and respond to player voice input using speech-to-text (STT).
  • Generate dynamic dialogue using large language models (LLMs) like GPT-4.
  • Speak with natural-sounding voices via text-to-speech (TTS) APIs.
  • Sync facial animations to speech using tools like NVIDIA Audio2Face.

Whether you’re developing an RPG, educational simulation, or experimental AI project, this guide walks you through the entire workflow—from setting up Unity to optimizing real-time performance. You’ll also find solutions to common challenges like lip-sync delays, AI response latency, and integration complexity, based on insights from developers who’ve tackled these issues firsthand.

What You’ll Learn

  1. Tools & APIs: Which speech/LLM services to use (OpenAI, Google, Inworld AI).
  2. Unity Setup: Importing models, rigging animations, and scripting interactions.
  3. AI Integration: Connecting STT/TTS APIs and training NPC personalities.
  4. Optimization: Reducing delays between voice input and NPC responses.
  5. Troubleshooting: Fixing common issues like desynced animations or API errors.

Let’s dive in!

Step-by-Step Guide to Creating Real-Time Voice-Enabled AI Talking NPCs in Unity
Step 1: Setting Up the Unity Environment

  1. Install Unity:
    • Download and install the latest version of Unity Hub and Unity Editor from the official Unity website: Unity Download.
    • Create a new Unity project.
  2. Install Required Packages:
    • Open your Unity project and go to Window > Package Manager.
    • Install necessary packages like Animation Rigging and Cinemachine for better animation control.

Step 2: Creating or Importing the NPC Model

  1. Create or Import Model:
    • Use a 3D modeling software like Blender to create your NPC model, or import a pre-made model into Unity.
    • Ensure the model is rigged for animation.
  2. Setup Animation Rig:
    • Use Unity’s Animation Rigging package to create a rig for your NPC model if it doesn’t already have one.

Step 3: Integrating Speech-to-Text (STT) and Text-to-Speech (TTS) APIs

  1. Choose STT and TTS APIs:
    • For STT, consider using OpenAI’s Whisper model, which can be run locally in Unity using the Sentis library: Whisper Demo.
    • For TTS, you can use Google’s Text-to-Speech API or similar services.
  2. Implement STT in Unity:
    • Use the Sentis library to integrate Whisper for speech-to-text functionality. Here’s a tutorial: Building AI-Driven Voice Recognition.
  3. Implement TTS in Unity:
    • Use Unity’s HttpClient to make API calls to your chosen TTS service.
using System.Net.Http;
using System.Threading.Tasks;
using UnityEngine;

public class TTSHandler : MonoBehaviour
{
    private string apiKey = "YOUR_API_KEY";
    private string apiEndpoint = "https://api.example.com/tts";

    async Task<string> GenerateSpeech(string text)
    {
        using var client = new HttpClient();
        client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", apiKey);

        var request = new HttpRequestMessage(HttpMethod.Post, apiEndpoint)
        {
            Content = new StringContent($"{{\"text\":\"{text}\"}}", System.Text.Encoding.UTF8, "application/json")
        };

        var response = await client.SendAsync(request);
        response.EnsureSuccessStatusCode();

        return await response.Content.ReadAsStringAsync();
    }
}

Step 4: Implementing AI-Driven Dialogue

  1. Choose an AI Model:
    • Use a conversational AI model like GPT-3 or GPT-4. For Unity integration, consider platforms like Inworld or Convai: Inworld AI.
  2. Integrate AI Model with Unity:
    • Use the chosen platform’s Unity plugin to connect your AI model with your NPC.
    • Ensure you have a way to seed the model with character backstories and context.
  3. Example of Using GPT-4 in Unity:
    • You can use OpenAI’s GPT-4 to generate NPC responses based on player input: Using GPT-4 for NPCs.

Step 5: Implementing Lip-Sync with Audio2Face

  1. Install Audio2Face:
    • Download and install Audio2Face, a tool for generating lip-sync animations from audio.
  2. Configure Audio2Face:
    • Set up Audio2Face to generate animations based on the audio generated by the TTS API.
    • Adjust settings for better lip-sync accuracy.
  3. Integrate with Unity:
    • Use a script to import the generated animations into Unity and apply them to your NPC model.
using UnityEngine;

public class LipSyncController : MonoBehaviour
{
    public void ApplyLipSyncAnimation(AnimationClip clip)
    {
        GetComponent<Animator>().Play(clip.name);
    }
}

Step 6: Real-Time Voice Processing

  1. Real-Time Audio Processing:
    • Use Unity’s audio processing capabilities to handle real-time audio input or output.
    • Ensure that the audio is synchronized with the NPC’s animations.
  2. Optimize Performance:
    • If running on a single machine, consider delaying audio playback to match animation rendering times.
    • For better performance, run Audio2Face on a separate machine to reduce latency.

Step 7: Testing and Deployment

  1. Test Your Setup:
    • Run your Unity scene and test the NPC’s voice and animation synchronization.
    • Adjust settings as needed for optimal performance.
  2. Deploy Your Game:
    • Once satisfied with the results, build and deploy your game to your desired platform.

Additional Resources

  • Whisper AI Demo: Unity-Sentis-Whisper
  • Inworld AI for Unity: Inworld AI
  • Tutorial on Building AI-Driven Voice Recognition: Building AI-Driven Voice Recognition

Troubleshooting Q&A
Q: How do I handle lip-sync delays when using Audio2Face?
A: To minimize lip-sync delays, consider running Audio2Face in headless mode on a separate computer. This can reduce the delay from 367ms to about 100ms.

Q: What are some common issues with using AI models for NPC dialogue?
A: Common issues include:

  • Response Time: AI models can take significant time to generate responses, making real-time interactions challenging.
  • Contextual Understanding: AI models may struggle to understand the context of conversations, leading to irrelevant or nonsensical responses.
  • Cost and Complexity: Implementing AI-powered dialogue can be costly and complex, requiring significant backend infrastructure.

Q: How can I optimize performance when using real-time voice APIs?
A: Optimize performance by:

  • Using Local Solutions: When possible, use local versions of speech-to-text and text-to-speech services to reduce latency.
  • Streaming Audio: Stream audio before the full clip is generated to reduce delays.
  • Resource Management: Ensure your system has sufficient resources (e.g., GPU power) to handle real-time processing.

Conclusion
Creating real-time voice-enabled AI talking NPCs in Unity involves integrating speech-to-text, text-to-speech APIs, and conversational AI models. By following these steps and utilizing tools like Whisper for STT and platforms like Inworld for AI integration, you can create engaging NPCs that enhance player experience in your games.

Example of AI-Driven NPC Conversations in MMORPGs:
You can see a demo of AI-driven NPC conversations in MMORPGs, such as World of Warcraft, using OpenAI’s GPT API and real-time voice acting AI: Demo Video.
LLM Integration into Unity:
For dynamic dialogue generation, consider using the LLM_Front-End system, which integrates OpenAI’s GPT API into Unity for NPCs with personality traits: LLM_Front-End.
Lip-Sync Tools:
For lip-syncing, tools like Nvidia Omniverse Audio2Face offer thorough solutions, though they require setup and may struggle with stylized faces: Audio2Face.
Open-Source Lip-Sync Tools:
Other open-source options include MuseTalk and LivePortrait, which can be used in video workflows but may require additional processing for real-time applications: Open-Source Lip-Sync Tools.
Replica AI Voice Actors:
For high-quality voice acting, consider using Replica AI Voice Actors, which offer a range of AI-generated voices suitable for various characters: Replica AI.