Hi VAPI team, I’ve connected Telnyx with VAPI and I’m seeing consistently very poor audio quality on live calls—so bad that the speech is unintelligible. Carrier: Telnyx (private German phone number) Call direction: Outbound calls from Germany to German numbers Example Call ID (VAPI): a66f05ee-1c0f-498c-a938-2d720272e401 example #2: 60d56822-b6a2-43a4-b824-9f3a356c16f9 Normal Telnyx-Integration is use; NO sip trunking! Telnyx feedback: Telnyx support says their side looks normal and suspects the issue is on the VAPI path. Expected: Clear, stable audio suitable for real-time conversation. Actual: Garbled/robotic/choppy audio; callers cannot understand the agent. Could you please investigate the call above and advise what might be wrong on the VAPI side or what configuration you recommend? If it helps, I can provide additional examples and do live test calls while you monitor. Thanks in advance! Sebastian

Suggestion: Check that your Vapi assistant is configured to use the correct audio format and sample rate for Telnyx SIP calls, as mismatches can cause severe audio distortion. In your assistant configuration, ensure the audio format is set to 16-bit PCM (

pcm_s16le

) and the sample rate matches Telnyx requirements (typically 8000 or 16000 Hz):

json
"audioFormat": {
  "format": "pcm_s16le",
  "container": "raw",
  "sampleRate": 8000
}

Update your configuration and test a call—this often resolves unintelligible audio issues caused by format mismatches. For further troubleshooting, review the call logs in the Vapi dashboard for any audio-related errors or warnings. Sources: - [WebSocket Transport](https://docs.vapi.ai/calls/websocket-transport) - [Debugging voice agents](https://docs.vapi.ai/debugging)

Is this only happening to you with Telnyx? I can't get any agent to have a decent audio quality anymore, even calling from the web. It's all glitchy and unusable pretty much.

I’ve worked on similar Telnyx + VAPI setups and poor audio usually comes down to how RTP is being handled or the media region VAPI is using versus the carrier. I can help you review your integration, check media region alignment, and run test calls to trace where the packet loss or codec mismatch is happening. Quick question: are you locking the assistant to the EU media server in VAPI or letting it default? @Sebastian7

Yes, it is only happening when using Telnyx. First I tried routing-settings in telnyx via Frankfurt/Germany. But if I leave the settings on default/Latency there is no difference. It seems that more users have problems with this kind of setup. I already found an easy alternative with a foreign twilio number that works fine, since I only need a demo version. I´ll try it again in the upcoming weeks/ months. Telynyx would in my special case still be my first choice, but I don´t have time for consuming experiments. Hope it might work easy some day. But thanks a lot to everybody reading and helping.

I understand—Telnyx setups can be tricky with VAPI due to codec or media region handling. I can help you directly analyze your integration, run focused test calls, and identify exactly what’s causing the poor audio. If you want, we can discuss this more privately and map out a quick solution so you can get Telnyx working smoothly when you’re ready. @Sebastian7

I'm in Australia. Got my Phone Numbers with Twilio. Since Monday, started noticing not just choppy audio but even sudden changes in intonation and weird artifacts that were not happening before. I'm using ElevenLabs voices and when doing the same call directly from ElevenLabs it just works perfectly. Haven't changed anything at all, this just started happening this week.

That makes sense, since ElevenLabs works fine directly, the issue is most likely in how VAPI is handling the audio stream with Twilio in your region. I can help you trace the media path, test with different regions/codecs, and quickly pinpoint what’s causing the artifacts. Let’s take this further in private so we can troubleshoot your setup directly. @Sam

This is not just me. There's multiple people reporting the same issue since this week. Check this: https://discord.com/channels/1211482211119796234/1422130421122072607

If you are using Telnyx, please make sure you disable HD voice in your phone number settings on the Telnyx settings.

Getting this same issue past few weeks. I am using ElevenLabs voices with Twilio numbers imported into Vapi, but also getting issue on Vapi free numbers. Exactly as Sam described, not just choppy audio but even sudden changes in intonation and weird artifacts that were not happening before on an assistant that has been in production for 1 year. This happened just as the client was going to commit to a major 6 figure expansion contract, and now they are on the fence because I haven't been able to resolve it after 40+ hours of debugging attempts. Still having the issues despite others reporting some improvement. Need a solution, this is the nth time Vapi performance issues have directly cost me money.

I can help figure out why your VAPI assistant’s audio is acting up, whether it’s the ElevenLabs voices, Twilio numbers, or the free numbers. We can pinpoint if it’s the voice engine, network, or assistant setup causing the glitches. Just to make sure I focus on the right thing—does this happen on all calls or only in certain situations? From there, I can map out a clear plan to get your assistant sounding consistent again. @mindofman

@Vercel it is seemingly random - it may happen multiple times on one call, or not at all on others, but typically at least 1 occurrence per call. Have youseen this issue before?

Yes, I’ve seen this kind of random distortion before, it usually points to a voice stream or buffer handling issue between ElevenLabs and Twilio rather than your setup itself. I can help you trace exactly where it’s happening and stabilize it long-term. Let’s connect privately so I can review your assistant’s config and logs in detail and assist you with the fix. @mindofman

There was some drift detections that happened within the past 12h that may have caused the distortion. Also, for our investigation please provide a call id where the distortion occurred and we will take a look at it