VAPI•4mo ago

Audio Recordings Out of Sync and Poor Call Quality with Twilio Number in Austria

I noticed that the audio recordings are not synchronized – the timestamps of the voicebot and the agent do not match at all and sometimes overlap when I connect my phone number.

I also experience major quality differences: via web call and chat everything works perfectly, but when using the phone number the quality is very poor.

Could you please help me understand what the issue might be and what options we have to resolve this?
For context: I am using a Twilio phone number and I am located in Austria.

still-limeOP•9/10/25, 12:35 PM

inbound call

Vapi Support BotAPP•9/10/25, 12:35 PM

Suggestion:
Try updating your squad or call configuration to use a different transportConfigurationstransportConfigurations provider (e.g., test with a non-Twilio provider if available) to see if the audio sync and quality improve. Here’s a sample config snippet:

"transportConfigurations": [
  {
    "provider": "twilio",
    "timeout": 60,
    "record": false
  }
]

"transportConfigurations": [
  {
    "provider": "twilio",
    "timeout": 60,
    "record": false
  }
]

If possible, switch "provider""provider" to another supported option and compare results. This helps isolate whether the issue is specific to Twilio's telephony routing in Austria.
See more in the API reference

Source:

Create Call API Reference

⤵️ Mention @Vapi Support Bot for follow-ups 🐥

still-limeOP•9/10/25, 1:51 PM

{
"assistantId": "{{ $json.agentTwoID }}",
"assistantOverrides": {
"variableValues": {
"current_time": "{{$now.format('yyyy-MM-dd T a')}}",
"day": "{{ $now.format('cccc') }}"
},
"firstMessage": "Hallo, ich bin Eva von Stia Immo. Unser Gespräch wird zu Qualitätszwecken aufgezeichnet. Wie darf ich Ihnen helfen!"
},
"recordingConfig": {
"separateAudioTracks": true,
"format": "wav",
"sampleRate": 16000
},
"transportConfigurations": [
{
"provider": "twilio",
"timeout": 60,
"record": false
}
]
}

still-limeOP•9/10/25, 1:53 PM

It seems like Vapi doesn’t properly wait for the bot’s initial start message, and in parallel it already records the caller’s speech on top of it... I tried your sugesstion ...

still-limeOP•9/10/25, 1:54 PM

...and also the option to include the start message again in the response. both does not work

still-limeOP•9/10/25, 4:04 PM

still-limeOP•9/11/25, 7:32 AM

I am also missing some words and answers in the transcript (phone call). I used the same words that I used for the web call....

still-limeOP•9/11/25, 7:37 AM

Two main problems:

The web assistant works well, but the phone assistant behaves differently (slower, lower quality, missing words/answers).

On phone calls, voice recordings overlap (bot + caller). Parts of both voices are missing → recordings are unusable, also in the trancript, see screenshots

Even though interruptions work as expected, the customer explicitly requires proper recordings, which are currently not possible.

Webcall = good relults. Phone call = unreliable and unusable.

VapiAPP•9/12/25, 11:07 AM

Hi,

Can you please provide a call id for both web call and phone call so we can compare the two? This information will help us find the differences in configuration

Ccomprehensive-tomato Hi, Can you please provide a call id for both web call and phone call so we can...

still-limeOP•9/12/25, 11:58 AM

webcall CallID: 724f3f23-cb5a-438f-98b1-d8fbd3776d14

Ccomprehensive-tomato Hi, Can you please provide a call id for both web call and phone call so we can...

still-limeOP•9/12/25, 11:59 AM

phonecall CallID: 6c8e2a92-85ff-4843-8bea-5548fd68db1a

Ccomprehensive-tomato Hi, Can you please provide a call id for both web call and phone call so we can...

still-limeOP•9/12/25, 12:00 PM

thank u, if you need further details pleae let me know, Gerald

Ccomprehensive-tomato Hi, Can you please provide a call id for both web call and phone call so we can...

still-limeOP•9/15/25, 8:59 AM

Hi Kyle, do you have any News ....?

VapiAPP•9/16/25, 9:06 AM

We analyzed both configurations and because there is higher latency in the phone call than the web call, you need to optimize your assistant for phone calls by switching the LLM to gpt-4o-mini and elevenlabs flash_v2_5 for a quick latency improvement. Please try making those changes then let us know if the phone calls need more improvement

still-limeOP•9/17/25, 8:20 AM

Settings "Flash_v2_5 and GPT4o mini ..." i am sorry it does not work ... callID 93e87bf3-b3e8-4da9-b80e-192a77d8a182

still-limeOP•9/17/25, 8:23 AM

Settings "Flash_v2_5 and GPT4o Cluster.." i am sorry it does not work ... callID 50bf0a1f-c35a-4daf-93f1-8a3ddd973d30

VapiAPP•9/19/25, 5:08 AM

Thank you for the call ids. We will review the contents and get back to you with an update

Ccomprehensive-tomato Thank you for the call ids. We will review the contents and get back to you with...

still-limeOP•9/24/25, 2:01 PM

do you have any News? rgds Gerald

VapiAPP•10/14/25, 11:54 PM

With current updates to the platform, please check if these updates have resolved your issue. Let us know if you are still experiencing this issue

Audio Recordings Out of Sync and Poor Call Quality with Twilio Number in Austria

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