How to Create AI Judge Metrics You Can Trust
How to use human review in Coval to calibrate your LLM-as-a-judge metrics: label conversations, check agreement, read disagreements, fix the prompt, and re-test.
Blog
Coval's observations on developing and shipping AI voice agents
We raised $28M. Here's what's next for us.
Time to First Audio, Measured Right: How a Benchmark Change Made TTS Faster
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Voice AI Benchmark: TTS and STT Results via API
How Coval continuously benchmarks 55+ TTS and STT models for latency and accuracy under production-realistic conditions.
Voice Agent Vendor Testing: How to Run a Bake-Off
How to run a voice AI vendor bake-off that picks the vendor your callers actually experience: the failure modes, the four shapes, and a defensible seven-step method.
Best STT Providers 2026: Independent Benchmarks & How to Choose
Best speech-to-text providers in 2026: Deepgram, AssemblyAI, Whisper, ElevenLabs Scribe, MAI-Transcribe. WER, latency, pricing. See the guide.
Best TTS Providers 2026: Why Vendor Benchmarks Lie
Best TTS providers in 2026: ElevenLabs v3, Cartesia Sonic 3, OpenAI Realtime, Deepgram Aura-2, Vapi Voices. Latency, pricing, voice cloning. See the guide.
Vapi Review 2026: Composer, Evals & Vapi Voices
Vapi review for 2026: Composer builder, Vapi Voices, Monitoring, Evals, Simulations, GPT-5 + Realtime, and post-Series B pricing. Read the guide.
ElevenLabs Voice Cloning Review 2026: v3, Scribe & Agents
ElevenLabs voice cloning in 2026: IVC vs PVC requirements, Eleven v3 vs Flash v2.5, Scribe v2 STT, ElevenAgents, and the May pricing reset. Read the guide.
CI/CD for Voice AI Agents: The 2026 Pipeline Guide
Voice agents are software. CI/CD pipelines with automated eval gates are how mature teams ship them. Patterns, tools, and pipeline design.
Voice AI Testing Build vs. Buy: When Internal Tools Hit a Wall
Voice AI testing build vs. buy: most teams build first, then hit the wall. The framework, the math, and what good buying actually looks like.
Voice AI Regression Testing: Escape Whack-a-Mole
Voice AI regression testing turns whack-a-mole shipping into safe iteration. Methodology, scenario design, and tooling for production teams.