Hey everyone! 👋 I've been deep in the trenches building voice calling agents for the past year, and I want to share something that's been a game-changer for our conversation quality—but almost nobody talks about it. The Problem You've Definitely Experienced You know that awkward moment when: - A voice AI cuts you off mid-sentence? 😤 - Or waits forever after you finish speaking? 🐌 - Or doesn't respond at all because it missed what you said? 🤷 That's not the LLM's fault. That's not even the speech recognition's fault. It's VAD and EOU detection failing. What Are VAD and EOU? Voice Activity Detection (VAD) = The system detecting "Is there human speech happening right now?" End-of-Utterance Detection (EOU) = The system detecting "Is this person DONE speaking, or just pausing?" These seem simple, but they're brutally hard to get right because: - A 500ms pause could mean you're breathing, thinking, OR finished - Background noise can trigger false activations - Different people speak at different speeds - Phone connections add artifacts - Accents and languages have different rhythms Why This Matters MORE Than You Think Natural human conversation happens fast. If there's more than 300ms between when you stop speaking and when the AI responds, it feels robotic. Your budget breakdown: - VAD/EOU detection: 50-100ms - Speech-to-Text: 100-200ms - LLM processing: 50-100ms - Text-to-Speech: 100-200ms Total: ~300-600ms ideally If your VAD/EOU takes 200ms, you're already in trouble before you even start processing what was said! Real-World Solutions (What I'm Using) Free & Open Source: - Silero VAD → Lightning fast (~1ms), great for controlled environments - WebRTC VAD → Battle-tested, super lightweight, less accurate but reliable - PyAnnote Audio → Transformer-based, higher accuracy but 50-100ms latency - Whisper VAD → Best accuracy across languages but slower (200-400ms) Commercial APIs (Production-Grade): - Deepgram → $0.0043/min, ~50ms latency, excellent noise handling (this is what I use) - AssemblyAI → $0.015/min, great with various accents - Picovoice Cobra → On-device, sub-10ms, perfect for privacy-sensitive apps