API Guide: Build a Vocal Chatbot with Real-Time Audio

The modern developer’s toolkit is a symphony of APIs. With a few strategic integrations, it’s now possible to build a real-time Vocal Chatbot, a sophisticated AI that can listen, understand, and engage in fluid, natural conversations. By orchestrating APIs for speech recognition, language processing, and voice synthesis, any skilled team can create a hands-free experience that feels remarkably human. This is the new frontier of user interaction.

This API-driven approach has democratized access to cutting-edge voice technology. However, after the initial thrill of building a successful prototype, many developers encounter a formidable and often project-killing roadblock. They discover that the elegant API pipeline that works flawlessly for a website or mobile app is fundamentally incapable of handling the most critical communication channel for any business: the telephone.

What is a Real-Time Vocal Chatbot?

A real-time Vocal Chatbot is a system that enables a live, spoken conversation between a user and an AI. Its defining feature is its ability to process audio as it’s being spoken, creating a seamless, low-latency dialogue. This is achieved through a high-speed, streaming pipeline orchestrated by APIs:

1. Audio Capture and Streaming: The user speaks, and their voice is captured and immediately broken down into small chunks. These are streamed to a backend server over a persistent connection like a WebSocket.
2. Live Transcription (ASR): A streaming Speech-to-Text API (like AssemblyAI or OpenAI Whisper) transcribes the audio chunks as they arrive, providing a continuous feed of partial and final transcripts.
3. AI Response Generation (LLM): The transcribed text is sent to a language model, which analyzes intent, accesses conversational context, and generates a response.
4. Streaming Synthesis (TTS): The AI’s text response is fed to a real-time TTS API (like ElevenLabs), which synthesizes the audio and streams it back to the user, often before the full response has even been generated.

When this API chain operates with sub-second latency, the result is a seamless, interruptible dialogue that feels truly conversational.

The Hidden API Challenge: Your Bot is Trapped in the Browser

You’ve successfully built this pipeline. Your Vocal Chatbot is a technical masterpiece. It’s fast, intelligent, and provides a stunning experience when users interact with it through your website. Now, your business wants to deploy this same assistant on its customer support hotline to handle calls. This is where the project grinds to a halt.

The problem is that the entire ecosystem of web-based APIs and protocols (like the Web Audio API and client-side WebSockets) was designed for the browser, not for the global telephone network. To make your bot answer a phone call, you face a completely new set of infrastructure challenges that no AI API can solve:

• Telephony Integration: You need to connect your application to the Public Switched Telephone Network (PSTN), a complex task involving SIP trunks and carrier relationships.
• Real-Time Media Servers: You have to build, deploy, and maintain servers capable of handling raw audio streams from thousands of concurrent phone calls.
• Call Management: You are now responsible for the entire call lifecycle, signaling, routing, and state management, for every single session.
• Network Resilience: Phone networks are prone to jitter and packet loss, which can garble audio. You must build systems to mitigate these issues.

Your bot, despite its brilliant API-driven brain, is trapped in a digital silo, unable to serve the millions of customers who rely on the telephone for important, time-sensitive conversations.

FreJun: The Infrastructure API for a True Omnichannel Vocal Chatbot

This is the exact problem FreJun was built to solve. We are not another AI API provider. We are the specialized voice infrastructure platform that provides the missing API, the one that connects the Vocal Chatbot you’ve already built to the telephone network.

FreJun handles all the complexities of telephony, allowing you to focus on orchestrating your AI services.

• We are AI-Agnostic: You bring your own “brain.” FreJun integrates seamlessly with any backend built on any combination of STT, LLM, and TTS APIs.
• We Manage the Voice Infrastructure: We handle the phone numbers, the SIP trunks, the global media servers, and the low-latency audio streaming from the PSTN.
• We Offer a Simple, Developer-First API: Our platform makes a live phone call look like just another WebSocket connection to your application, delivering a clean, bi-directional audio stream that you can pipe directly into your existing AI logic.

FreJun provides the robust, scalable, and reliable infrastructure that connects your real-time AI to the real world.

Pro Tip: Design a Channel-Agnostic AI Core

The most efficient and scalable way to build a Vocal Chatbot is to create a centralized backend that houses your core AI logic. This “brain” should be designed to simply process an input and produce a response, regardless of whether the request came from your web app, your mobile app, or a FreJun-powered phone call. This approach ensures a consistent user experience and makes your system much easier to maintain and update.

The Web-Only Vocal Chatbot vs. The FreJun-Powered Omnichannel Vocal Chatbot

Feature	The Web-Only Vocal Chatbot	The Omnichannel Vocal Chatbot (with FreJun)
Accessibility	Limited to users who are actively on your website or in your app.	Universally accessible to anyone with a phone, plus all digital channels.
Infrastructure Burden	Low for web deployment. Immense if you attempt to build your own telephony.	Zero telephony infrastructure to build. FreJun manages the entire voice stack.
Primary Use Case	On-site guidance, digital lead capture, simple FAQs.	24/7 call centers, virtual receptionists, automated phone orders, critical incident support.
Business Impact	A modern UX feature that improves digital engagement.	A strategic asset that reduces operational costs and serves all customer segments.
Developer Focus	AI logic and client-side web technologies.	AI logic and delivering business value across all channels.

A Step-by-Step API Guide to Building a Complete Vocal Chatbot

This guide outlines the modern architecture for creating a single AI assistant that can handle real-time audio from both your website and the phone.

Step 1: Architect Your Backend for API Orchestration

First, build your core conversational logic. Using your preferred backend framework (like FastAPI or Node.js), write the code that orchestrates the API calls to your chosen STT, LLM, and TTS services. This channel-agnostic “brain” will be the heart of your Vocal Chatbot.

Step 2: Implement Your Web-Based Frontend

For your website, use client-side JavaScript to capture microphone audio. Establish a WebSocket connection from the browser to your backend and stream the audio chunks to your AI core.

Step 3: Add the Telephony Channel with FreJun’s API

This is the critical step that makes your bot truly omnichannel.

1. Sign up for FreJun and instantly provision a virtual phone number.
2. Use FreJun’s server-side SDK in your backend to handle incoming WebSocket connections from our platform.
3. In the FreJun dashboard, configure your number’s webhook to point to your backend API endpoint.

Step 4: Route All Audio Streams to Your AI Core

Your backend will now receive audio streams from two different sources. When a connection is established, you simply pipe the incoming audio whether it’s from a browser WebSocket or a FreJun WebSocket into the same AI core you built in Step 1.

Step 5: Stream the Response Back to the Correct Source

Once your AI core generates a synthesized audio response, you stream it back to the connection it came from. If it was a browser, it goes back to the browser. If it was a FreJun-powered phone call, it goes back to the FreJun API, which plays it to the caller with ultra-low latency.

With this unified architecture, you have a single, intelligent Vocal Chatbot that can seamlessly handle real-time conversations from any channel.

Key Takeaway

You need two distinct types of APIs to build a complete, production-ready Vocal Chatbot. First, you need a set of AI APIs (for STT, LLM, and TTS) to build the bot’s intelligence. Furthermore, you need a robust voice infrastructure API to connect that intelligence to the real world. Therefore, FreJun provides this second, critical API, consequently handling all the complexities of telephony so you can focus on building the smartest assistant possible.

Best Practices for a Flawless Real-Time Experience

• Optimize for Low Latency: A natural conversation requires speed. Use persistent WebSocket connections, keep audio buffer sizes small, and choose AI providers that offer low-latency streaming responses.
• Handle Multi-Turn Dialog and Context: Use a fast database or in-memory cache to store the session state for each conversation, allowing your bot to have intelligent, multi-turn dialogues.
• Manage Security: Use encrypted channels (TLS) for all API calls, secure your credentials, and comply with all privacy regulations for voice and transcript data.
• Continuously Monitor and Analyze: Implement comprehensive logging and monitoring to track your bot’s performance, identify errors, and gather data to improve its conversational flows.

Final Thoughts: Your AI is Brilliant. Make Sure It Can Be Heard.

The API economy has made it possible to build a real-time Vocal Chatbot with stunning capabilities. Furthermore, you now have the intelligence, the voice, and the conversational flow all within your reach. However, the true measure of a business-ready solution is not just its intelligence; rather, it’s its accessibility.

Don’t let your brilliant creation be limited by the confines of a web browser. Instead, by adopting a true omnichannel strategy from the start, you can transform your voice bot from a modern website feature into a powerful, 24/7 workhorse for your entire business. Furthermore, the path to this transformation doesn’t require you to become a telecom company. Rather, it requires a smart API strategy that combines the best AI tools with a robust voice infrastructure partner.

Let FreJun handle the connection, so you can perfect the conversation.

Try FreJun Teler!→

Further Reading – Real-Time Conversational AI Voice Integration Using APIs

Frequently Asked Questions (FAQ)