🗣️ Amazon Polly
Why it was created
- To convert text into natural-sounding speech
- Solves the problem of adding voice output to apps without building TTS engines
Core idea
👉 “I have text. I want audio.”
What it does
- Text → Speech
- Multiple voices, languages, accents
- Neural voices for human-like sound
Typical uses
- Voice assistants (output only)
- Audiobooks
- Accessibility (screen readers)
- IVR systems reading messages
🤖 Amazon Lex
Why it was created
- To build chatbots and conversational interfaces
- Uses the same tech as Alexa
- Solves understanding user intent from text or voice
Core idea
👉 “User talks or types. System understands and responds.”
What it does
- Speech → Text
- Natural Language Understanding (NLU)
- Intent detection, slot filling, dialog flow
Typical uses
- Chatbots (support, HR, banking)
- Voice bots
- Conversational interfaces in apps
🔑 Key Concept Difference (Exam Gold)
Polly talks. Lex listens and understands.
📊 Amazon Polly vs Amazon Lex Comparison Table
| Feature | Amazon Polly | Amazon Lex |
|---|---|---|
| Primary Purpose | Text-to-Speech | Conversational AI |
| Main Function | Converts text into audio | Understands user intent |
| Input | Text | Text or Voice |
| Output | Audio (speech) | Text or structured response |
| Speech Recognition | ❌ No | ✅ Yes |
| Natural Language Understanding | ❌ No | ✅ Yes |
| Dialog Management | ❌ No | ✅ Yes |
| Uses Machine Learning | Yes (speech synthesis) | Yes (NLU + ASR) |
| Typical Integration | Apps, IVR, media | Chatbots, voice bots |
| Alexa Technology | ❌ No | ✅ Yes |
| Accessibility Use | ✅ Strong fit | ❌ Not primary |
🎯 Real-World Example (Easy Memory Hook)
Banking App
- Amazon Lex → “What is my account balance?”
- Amazon Polly → Reads out: “Your account balance is $5,000.”
👉 Lex understands the question
👉 Polly speaks the answer
✔ Choose Amazon Polly when:
- Question says “convert text to speech”
- Mentions audio output
- Accessibility, narration, reading messages
- No chatbot or intent detection required
🚨 Trap: If there is no user conversation, Lex is overkill
✔ Choose Amazon Lex when:
- Question says chatbot, conversational interface
- Mentions intent, slots, dialog
- Voice or text input from users
- Alexa-like experience
🚨 Trap: Lex does NOT generate natural speech like Polly (it may integrate with Polly, but Polly is not Lex)
🧩 How They Work Together (Common Architecture)
- User speaks → Lex converts speech to text
- Lex understands intent
- Backend processes request
- Response text sent to Polly
- Polly converts response to speech
💡 Lex = Brain
💡 Polly = Voice
🧪 TL;DR
- Amazon Polly: Text → Speech
- Amazon Lex: Speech/Text → Intent
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