#Anyone using Telnyx Sip Trunking and

1 messages · Page 1 of 1 (latest)

granite valley
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Where is your phone number and calls based? We are having trouble with the audio quality with our twilio numbers in germany. The pstn network which telephony calls are routed through only allows for narrowband audio which is below 8khz. This leads to transcription problems for us.

drifting rune
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I have hugee transcriptions problems

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I'm in Italy and using Telnyx

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Sip trunking

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Used all three available codecs, G711U, G711A and also used G722 (that is working atm), but still metallic voice

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Do you have any tips for this?

granite valley
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italian pstn is also on 8khz afaik and does not support g722. The main problem is that even though telnyx supports g722 as soon as the audio goes through pstn it is below narrowband. We haven't found a solution to this yet honestly and are still looking. Same situation in germany

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The problem is systemic in the public networks. So the only improvement I can see in the future is voip, volte or the transcription models are improving accuracy on 8khz audio

drifting rune
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Using a websocket would change quality from your point of view?

granite valley
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Yes webrtc / direct sip to sip allows for 24khz or more but as soon as calls are routed thorugh pstn the quality is gone. I dont know exactly yet how this will be managed once pstn is turned off. In germany it is set to shut off in 2025 in italy there is no date set

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afaik telnyx offer pstn replacement

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routing through ip only

drifting rune
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But so classic Websocket throught supabase passing from Telnyx <-> Elevenlabs will not have a better connection correct?

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Btw thanks for the infos

granite valley
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when someone calls from a normal phone number the call always goes through the global phone network somewhere. even if they use voLTE or some fancy voip on their side it usually gets downgraded to narrowband once it hops between carriers. after that point you just cant get the quality back. telnyx can send the audio to you over websocket but it can only pass on what it got so it wont magically upgrade anything. you only get real wideband if both sides stay fully on IP and the call never touches the old phone network at all.

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seems in italy pstn is still standard for most carriers

drifting rune
# granite valley check this out: https://telnyx.com/resources/pstn-replacement

Totally makes sense, thanks for the detailed explanation.
So basically if I want to keep using a normal phone number, the only realistic way to get better audio quality is to go with a Telnyx PSTN Replacement setup, right?
That way the call stays fully on IP end-to-end and never touches the legacy PSTN, so I could finally use higher bandwidth codecs and actually get wideband audio into my AI pipeline

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Correct?

granite valley
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i checked the telnyx pstn replacement now and basically it seems it just switches the internal telnyx network to full voice over IP. it does not magically fix the audio from the caller side. so if someone calls from a carrier that is not using voice over IP or voice over LTE the audio is already narrowband when it hits telnyx. and even if the caller uses volte it can still drop back to narrowband when the call hops between carriers. so in the end it still will not work reliably for hd audio.

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in the us hd voice works way better because most carriers are already fully on volte and they have direct ip interconnects between each other. so the call usually stays on the same wideband path without dropping back to narrowband. there are fewer carriers and less old legacy routing so the audio does not get downgraded like it does in europe.

drifting rune
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Thanks a lot for the clarification, that makes total sense.
So even with Telnyx PSTN Replacement in Italy, the caller audio will still be narrowband if the originating carrier downgrades it before hitting Telnyx, right?

Basically: PSTN Replacement avoids additional degradation on Telnyx side, but it doesn’t fix the fact that most EU carriers don't keep calls on VoLTE end-to-end.

So for consistently higher quality atm there are no real solutions..

granite valley
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Not in many european countries sadly. I am hoping german carriers adopt it 100% asap. In italy it is still slow i think.
As long as it goes through pstn from the caller carrier or carrier hopping the quality is rip

drifting rune
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Got it, thanks.

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Do you think there’s any benefit in routing my Italian DID through a US Telnyx POP instead of the EU one?

Idea would be:

  • keep a normal +39 number
  • but let Telnyx ingest the call on the US side
  • so the call stays fully on IP inside the US backbone, where wideband/VoLTE interconnects are more stable

I know it won’t fix PSTN, but in cases where the caller’s carrier does support VoLTE/IP peering, the audio might hit Telnyx with less degradation than when routing through EU legacy hops.

Do you think this could give any improvement, or is it basically the same once the first narrowband hop happens?