Outbound call is distorted on the callee's end - n...
# supporte
Enyedi Péter
04/10/2025, 9:38 AMMy phone number provider is Telnyx. You guys said that the problem regarding the outbound call (very distorted) is on telnyx's side but it is certainly not. I contacted the support and they sent me audio samples from the recorded calls, and my voice was crystal clear. They said it is possible that it is a codecs problem and I should control the codecs of my voice API agent.
Example call ID: 3e5c9ca3-b989-4eed-a8da-0924275d2546
What telnyx said: According to investigation on our internal team we could not find any problem in our side. According to some examples of your calls have clear understanding RTP packages attached on mail. The recordings are clearly understandable and we could not find any codec/quality problem in our side. Could you please control your Voice Api Agent to codecs or control your device with problems about that.
I also attached the audio, what Telnyx sent and the Call Data Debugging, from their site, regarding my call.
@User @User @User
https://cdn.discordapp.com/attachments/1359824858242093117/1359824858472648784/user.wav?ex=67f8e316&is=67f79196&hm=ac9de3e5ad6b8b013c196c3201bb397568cb93cf38ad47f40bc7ae3be3036c13&
Enyedi Péter
04/10/2025, 10:31 AMCall Data Debugging
Enyedi Péter
04/10/2025, 12:57 PM@Pigeon could you help me out?
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Pigeon
04/10/2025, 12:58 PMI never used telnyx, sorry
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Enyedi Péter
04/10/2025, 1:00 PMdo you have any idea where can I find the codecs settings in VAPI? Or the settings for outbound calls?
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Pigeon
04/10/2025, 1:01 PMNope, never needed that
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Shubham Bajaj
04/10/2025, 3:26 PMlooking into it.
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Enyedi Péter
04/11/2025, 8:47 AMthank you Shubham, do you have any update?
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Kyle Brunker
04/11/2025, 6:55 PMFor Telenyx. we use PCMU codec (G.711 μ-law) with 8kHz sampling rate, mono audio in 20ms chunks for the imported Telenyx numbers
Kyle Brunker
04/11/2025, 6:56 PMFor your information, we also have a dedicated channel with them. If that was the case, they would have also informed us. In case you are saying our codecs are wrong, happy to make the changes. Let me know the changes required, and there are some citations so that I can read them through and then eventually update the team if any changes are required.
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Kings_big💫
04/11/2025, 7:32 PM@Enyedi Péter
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Enyedi Péter
04/11/2025, 7:47 PMThank you Shubham, will contact Telnyx again to provide them the information you said, and then I will come back with an answer if it needs to be updated or not, or what could be the problem.
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Kyle Brunker
04/11/2025, 10:13 PMPlease @Enyedi keep me updated if it's a potential issue, and because of us we have to fix it. I'm keeping an eye on this issue.
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Enyedi Péter
04/12/2025, 4:34 PMwill text here in this ticket, if I get a response from Telnyx, thanks.
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Kyle Brunker
04/12/2025, 5:13 PMAlright
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Enyedi Péter
04/16/2025, 1:36 PMgot the feedback from Telnyx. They said:
Hello Peter,
Can you ask the VAPI for the details on their end? I mean in our end we could not find any packet loss or quality issues. If they want we can investigate the issue together with the Vapi team. For codecs we accept many types of codecs (PCMU,PCMA,G711 etc.)
Enyedi Péter
04/16/2025, 1:43 PMAnd I want to mention that for inbound calls I use G711-U on Telnyx and this is the only codec that works for me because the when I try to select other codecs all of them are distorted except the G711-U when doing inbound calls.
So my guess is I would have to use G711-U for outbound too right? But even if I use it it is distorted when doing outbound calls.
Enyedi Péter
04/20/2025, 3:03 PM@Sahil @Kings_big💫 @Shubham Bajaj
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Sahil
04/20/2025, 3:48 PMGive it a shot.
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Enyedi Péter
04/20/2025, 5:58 PMwhat do you mean?
Enyedi Péter
04/20/2025, 5:59 PMis there a way you can change my codec? To use just one codec? (G711U)
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Kyle Brunker
04/21/2025, 8:05 PMIf you import Telnyx numbers based on SIP, then you can only select a single codec which is G.711U. You can follow our documentation on how to set up your SIP trunk with Telnyx. You can check the SIP tracking guide where we have configured codecs to be selected for inbound and outbound calls, and you can configure it to be G.711U. Let me know if you require further help on this.
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Kings_big💫
04/21/2025, 10:59 PM@Enyedi Péter
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Enyedi Péter
04/22/2025, 5:17 PMalso tried this way, but it didn't solve the problem for me.
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Kyle Brunker
04/23/2025, 12:39 AMPlease provide details of your issue and steps taken to resolve it. This will help me understand your challenges and tailor suggestions. I can propose new solutions or enhance existing approaches.
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Enyedi Péter
05/05/2025, 5:48 PMI have contacted telnyx and they said the following: Can you ask the VAPI for the details on their end? I mean in our end we could not find any packet loss or quality issues. If they want we can investigate the issue together with the Vapi team. For codecs we accept many types of codecs (PCMU,PCMA,G711 etc.)
Thank you for your patience.
Enyedi Péter
05/05/2025, 5:48 PM@Shubham Bajaj
Enyedi Péter
05/05/2025, 5:48 PM@Kings_big💫
Enyedi Péter
05/05/2025, 5:51 PMI think it is a codecs issue, on Telnyx's end the sound is clear, but on VAPI log calls my sound is very distorted
Enyedi Péter
05/05/2025, 5:52 PMI tried setting g711u only on telnyx, it didn't solve the issue
Enyedi Péter
05/05/2025, 5:53 PMor is there a way I can change/set my codec in VAPI too?
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Kyle Brunker
05/06/2025, 9:10 PMHey Peter,
First and foremost, I would like to sincerely commend you for your diligent follow-up with the team and for keeping us updated. Your efforts are truly commendable and greatly appreciated.
If you could kindly share any recent call IDs where you experienced voice distortion, along with the corresponding timestamps, I will personally look into it and ensure a thorough investigation is conducted.
Thank you once again for your dedication.