Hey everyone 👋 I’m building a Vapi outbound agent using a Telnyx German number. The agent successfully places the call, but doesn’t react to what the customer says — it’s like it can’t hear them. However, in the Vapi call logs, I can see that both voices are recorded, so audio seems to be flowing in both directions. Does anyone have an idea what could cause this? Maybe something related to STT/TTS setup (Deepgram + OpenAI) or Telnyx RTP settings? Any tips would be super appreciated 🙏 call id: 0199ee4a-5ee5-7113-b16c-a4a170fb67b6

A common issue is incorrect transcriber configuration. Try explicitly setting Deepgram as your transcriber and ensure the audio channel is set to mono (1 channel), as shown below:

json
"transcriber": {
  "provider": "deepgram",
  "language": "de",
  "channels": 1
}

Update your assistant config with this and test again—this often resolves agent non-responsiveness when audio is present but not recognized. Source: - [Custom Transcriber Documentation](https://docs.vapi.ai/customization/custom-transcriber)

Hey! We tried forcing the Deepgram transcriber to mono (channels: 1) since the customer audio sounds clean in Telnyx but distorted in Vapi. However, the dashboard doesn’t let us edit JSON, and the API PATCH /assistants/... returns 404 — looks like assistant updates aren’t supported. Any way to make Deepgram process mono audio or set this at the Telnyx level?

Hey! I’ve run into something like this before — it’s usually because Telnyx sends stereo audio while Deepgram expects mono. I can help you adjust the Telnyx stream or set up a quick workaround so Deepgram processes it correctly. Just to confirm, are you using Telnyx through WebRTC or SIP for your outbound calls? That’ll help narrow it down. @Robel

hi, thanks for your reply! i am using telnyx sip for my outbound calls. Do you know how i can fix this? @Vignxt Flow

Got it, since you’re using Telnyx SIP, the issue is most likely that Telnyx sends stereo RTP audio while Deepgram only processes mono. I can help you fix this by updating your SIP connection settings to send a single mixed audio channel, or by adding a lightweight audio downmix step before it reaches Deepgram. If you can share your current SIP connection or webhook setup, I can point out exactly where to make the change. @Robel

Please also make sure

HD Audio

is disabled on the telnyx side to improve audio quality on Vapi