How to Choose the Best TTS, STT, and LLM Combo for Your AI Voice Agent

If you've started exploring AI voice agents, you've come across STT, LLM, TTS. Understanding these — even at a basic level — helps you make smarter platform decisions.

The Three Layers

1. STT — Speech-to-Text (the ears)
2. LLM — Large Language Model (the brain)
3. TTS — Text-to-Speech (the voice)

Flow: Caller speaks → STT transcribes → LLM generates response → TTS speaks it. All in under 2 seconds.

STT — Speech-to-Text

Listens to what the caller says and converts to text. Key factors:

• Accuracy — especially with accents, noise, casual speech
• Language support — many STTs struggle with Indian accents
• Speed — milliseconds matter

Vaaad AI uses: Deepgram — fastest, most accurate for real-world Indian speech.

LLM — Large Language Model

The brain. Reads transcription, understands intent, generates response. Key factors:

• Reasoning quality — handles ambiguous responses
• Instruction-following — stays on script
• Latency — impacts total response time
• Cost — scales with volume

TTS — Text-to-Speech

The voice. What your caller experiences most directly. Key factors:

• Naturalness — human-like rhythm and intonation
• Language/accent support — critical for Indian businesses
• Speed — affects total latency

Vaaad AI uses: Sarvam AI — built natively for Indian languages, not retrofitted from English.

How the Three Layers Work Together

Caller speaks (Hindi / Tamil / Punjabi / English)
        ↓
Deepgram (STT) — milliseconds
        ↓
LLM — understands + generates response
        ↓
Sarvam AI (TTS) — natural Indian-language speech
        ↓
Caller hears response (within 1-2 seconds)

How to Choose the Right Combo

1. What languages do your customers speak? — narrows choices significantly
2. How important is voice naturalness? — sales vs operational calls
3. What's your latency target? — under 2s requires fast STT+TTS
4. What's your call volume? — costs add up at scale
5. How complex is your conversation? — simple scripts need less LLM power

The Honest Takeaway

There's no single “best” combination. What Vaaad AI has done is make specific choices — Deepgram + Sarvam — optimised for Indian businesses, tested, and ready to use. You don't need to figure out the stack yourself.

Try Vaaad AI free — see how the full stack performs on your first real call.