🔊 Voice & Audio · 3-Way Comparison
AssemblyAI vs Cartesia Sonic vs OpenAI TTS
AssemblyAI vs Cartesia Sonic vs OpenAI TTS: 3-way head-to-head scored on Performance, Value, Reliability, and Ease of Use. See scores, pros, cons, and our verdict for each tool.
🏆
Top Pick
AssemblyAI8.8/10
AssemblyAI leads with 8.8/10 overall. Best speech-to-text API for developers. LeMUR feature adds LLM reasoning over audio.
Top Pick
AssemblyAI
AssemblyAI
8.8
/ 10
Cartesia Sonic
Cartesia
8.6
/ 10
OpenAI TTS
OpenAI
8.8
/ 10
Score Breakdown
| Dimension | ★ Top Pick AssemblyAI AssemblyAI | Cartesia Sonic Cartesia | OpenAI TTS OpenAI |
|---|---|---|---|
Performance Benchmark scores & output quality | 8.8 | 9▲ | 8.5 |
Value Price-to-performance ratio | 8.5 | 8.5 | 9▲ |
Reliability Uptime, stability & vendor risk | 9 | 8.5 | 9 |
Ease of Use Interface, docs & setup friction | 9 | 8 | 9 |
| Overall Score | 8.8 / 10 | 8.6 / 10 | 8.8 / 10 |
Tool Details
🏆 Top Pick
AssemblyAI
AssemblyAI · Pay-as-you-go $0.012/min · Custom enterprise plans
Best speech-to-text API with LLM reasoning over audio
✓ LeMUR adds GPT-4 reasoning over transcribed audio
✓ Speaker diarisation, auto-chapters, sentiment analysis
✗ More expensive than Whisper for high volumes
Cartesia Sonic
Cartesia · Free (50K chars) · Pay-as-you-go $0.0025/1K chars
Fastest TTS API — 90ms latency for real-time voice
✓ 90ms latency — fastest in market for real-time use
✓ Instant voice cloning from 5 seconds of audio
✗ Smaller voice library than ElevenLabs
OpenAI TTS
OpenAI · API: $15/M characters (TTS-1) · $30/M (TTS-1-HD)
Best value TTS for scale
✓ Fast generation — suitable for real-time apps
✓ 6 built-in high-quality voices
✗ No voice cloning