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If calls connect but the audio is wrong and you’ve ruled out your own endpoint, this page is organized by the symptom you’re hearing. Find it in the headings below and follow the fix. Each section is self-contained, so you can land here from a search result and still get what you need. If your symptom isn’t listed, jump to Still stuck? for what to send us so we can trace it on our side.

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Callers hear choppy or distorted AI audio

The caller hears the AI voice as choppy or warbly, but the other direction is clean — the AI platform’s transcription and its own recording sound fine. Spectrum uses G.711 for call audio to keep quality consistent. It’s the codec the phone network itself runs on, and it holds up on the mobile networks most callers are on. If your AI audio is choppy anyway, check the codec in your endpoint’s 200 OK. It should say PCMU/8000 or PCMA/8000 — if it says anything else, or it’s choppy even on those, jump to Still stuck? and include the codec in your report.

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Audio sounds like a regular phone call, not HD

That’s expected — G.711 is standard telephone quality. Consistent audio on every call beats HD on some and garbled audio on the rest.

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One-way or missing audio

Spectrum only handles signaling. The audio itself (RTP) flows directly between the carrier and your SIP endpoint, so when sound is missing in one direction the problem is usually at one of those two ends:
  • Make sure your endpoint (or its cloud provider) accepts inbound RTP from the carrier’s media IPs, not just SIP signaling.
  • If your endpoint sits behind NAT, it needs to advertise a publicly reachable address in its SDP, not a private one.
  • Check your endpoint’s media logs for RTP timeouts or packet-receive errors on the affected call.

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Still stuck?

Send us:
  • Your project id (from photon projects show).
  • The SIP Call-ID, or the call time, caller number, and dialed number so we can find it.
  • The direction (inbound or outbound) and which side hears the problem.
  • The negotiated codec from the 200 OK, if you can capture it.
  • Your downstream SIP endpoint vendor (ElevenLabs, Retell, self-hosted, …).
We’ll trace the call on our side, including the exact SDP each leg saw. Email us at [email protected] or ping us in the Discord linked in the footer.