Critical Audio Quality Issue — Telnyx + VAPI (Programmable Voice)
Hi everyone,
I’ve been facing a critical audio issue between Telnyx (Programmable Voice) and VAPI. I’ve been testing different setups for over a week now, with no results.
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Summary
Technical context
Additional notes
What I’m looking for
I’ve been facing a critical audio issue between Telnyx (Programmable Voice) and VAPI. I’ve been testing different setups for over a week now, with no results.
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Summary- I call a Telnyx number connected to VAPI.
- The assistant speaks → I hear it perfectly.
- I speak → my voice is severely degraded on VAPI’s side (robotic, choppy, unintelligible).
- When the AI transfers the call to a human on a French landline (still via Telnyx) → call quality becomes perfect again.
- On two different phones (same issue),
- Using the Telnyx server in San Jose (USA) to simulate a worst-case scenario — yet no audio issue during the human transfer phase.
Technical context- I’m in Paris (France), using fiber internet, Wi-Fi Calling, and a stable mobile carrier.
- VAPI’s servers are also based on the US West Coast, so the connection between Telnyx and VAPI should be solid.
- These tests show the issue is not related to my phone, network, or Telnyx itself, but likely how VAPI receives incoming audio from Telnyx (Programmable Voice).
Additional notes- With **Telnyx SIP Trunking**, the issue disappears — but:
- It’s not the default or recommended setup,
- And it doesn’t support call transfers, which is a dealbreaker for me.
What I’m looking for- A response from the VAPI team regarding this behavior.
- Ideally, an official recommendation to ensure stable audio quality with working call transfers.
