Agent TTS audio is badly distorted (“robotic”) on all web/WebRTC calls — clean on PSTN. Isolated to server-side web media.

Support Help
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The agent’s spoken voice is heavily distorted — robotic/metallic/garbled — on every browser (web) call, while the same agent, same voice, over a PSTN phone call sounds perfect. We’ve isolated it to the audio you deliver on the WebRTC path, not our client, device, or network.
What we’ve already ruled out (please don’t send us to the headphones FAQ — we did the differential):
• Not the front-end. It reproduces identically in two independent clients: (a) your own dashboard “Test Call” widget, and (b) our own integration built directly on retell-client-js-sdk v2.0.8 (RetellWebClient.startCall({ accessToken }), call created via POST /v2/create-web-call). Same distortion in both → it’s in the media stream you send, not the renderer.
• Not mic/STT. The agent understands us perfectly and responds correctly. The defect is strictly agent → listener (playback): it’s the agent’s voice that’s mangled.
• Not our device/OS/browser. Same machine, same wired headphones: Google Meet and other WebRTC calls are crystal clear. Only Retell web calls are affected.
• Not the agent content. The exact same agent + voice over PSTN (Twilio) is flawless.
Why we believe it’s a server-side sample-rate / resample problem: The defect is present on the wideband WebRTC path but masked on the 8 kHz narrowband PSTN path — the classic signature of a sample-rate mismatch or a bad resample when the TTS PCM is packetized onto the WebRTC/Opus (LiveKit) track. It’s pitch/timbre distortion (“robot”), not dropouts, jitter, or latency.

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Hey @zparxmarketing Can you share the relevant Call IDs?

Thank You

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It does this when attempting to “Test Audio” within any of the agents configuration pages.

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call_218c0fdb65c16d245faa57c29c4

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@zparxmarketing Okay, I’m checking this with the team and will get back to you as soon as I have an update.

6

Hey @zparxmarketing Could you please try a different voice provider, such as Cartesia or ElevenLabs, and let us know whether the issue still occurs? This will help us determine whether the issue is specific to a particular provider.

Thank You