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Is BT Digital Voice the best option for HD quality calls?

Elms64

Member
This question is about the audio quality of the various UK landline telephone service providers.

I am currently with BT for my landline phone and line rental. Plusnet for my broadband (ADSL with 17 Mbps download speed, which is fine for my Internet usage).

But with BT turning off their analogue landlines in 2025, I have to either switch my landline to BT Digital Voice (which I believe requires that I also use BT broadband).

Or alternatively I could use another provider such as Virgin Media for my landline telephone and broadband (at my address in London, Virgin offers fibre speeds up to 1130 Mbps).

Or another option would be to terminate my BT landline phone, and switch to one of the many third party companies offering VOIP telephone services.

But my question is about the audio quality of the landline telephone service.

I live with elderly parents who are both hard of hearing, and call clarity and quality is important for them, otherwise they can miss important information (when talking to their doctor on the phone, etc).

BT claim their Digital Voice system offers a high audio quality named "HD calling". Although I understand that in order to obtain this high quality, you need to use BT's own DECT phones (such as the Essential Digital Home Phone) which wirelessly link to the BT Smart Hub 2 router. And I understand this high audio quality also requires the person at the other end of the line to be using BT Digital Voice, or using a mobile on the BT-owned EE network.

So I wonder if BT Digital Voice would offer better call audio quality than a landline phone provided by Virgin? Does anyone know how the audio quality of BT Digital Voice would compare to a Virgin phone?

And how would Digital Voice audio quality compare to the audio quality of third party VOIP telephone providers?

Thanks in advance for any insight anyone can give on this sound quality issue.
 
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I use A&A Which is the same quality you would get using a basic analog BT Landline. Perfectly clear but no fancy extras like HD Voice.

I have used BT Digital voice. If you call another customer who uses the same service, or you call the likes of customer service on 150 with a handset that supports HD voice then it sounds like you're making a call with a mobile phone on 3G or 4G that supports HD Calling. The same kind of call quality. That slight background hiss is gone and you get a little more clarity in the voice. The problem is you rarely get to hear it because not many other people or providers will be using a compatible service.

Virgin's digital landline is about the same as any other analog line too, but in the case of my old HFC Line with high latency and minor packet loss which VM consider to be well within tolerance and not a fault - You will hear the occasional glitch, distortion or momentary cut-out. Most people will never hear this especially if they are covered by VM's full fibre instead. But for this reason I would consider them to be the worst.

I can also say I have used Vonage in the past. I found them to be just as good as any analog line but as an added bonus for older people who may be hard of hearing, the default volume level on the line was noticeably higher than you would get if you plugged in to an alalog socket.
 
I am using Andrews&Arnold and Freevoipdeal for VoIP telephony. A&A only offer G.711 (standard digital voice). On Freevoipdeal some calls get connected as HD voice (G.722 HD), others as G.711. I have to say that I would not be able to tell the difference when making a call (only the logs reveal this) although G.722 covers frequencies up to 7kHz, G.711 cuts off at 3.1 kHz. I suspect that even if the connection from my phone and Freevoipdeal Server is HD, the remaining part (FVD onto called party) is still G.711.

Even if BT DV supports HD Voice, this does not guarantee that all calls will be HD end-to-end. They should be HD voice as long as it is between two BT DV subscribers, but once the call is between customers on different networks, there is no guarantee that they will get HD voice end-to-end.

So, as far as I am concerned HD telephony is at present not much more than a sales gimmick. Only if the majority of operators have HD voice, will it make a real difference.

VoIP has the advantage that you are no longer restricted to buy a telephony service from whoever runs the copper cable to your house (or one of their resellers), but that once you have decent broadband, you are free to chose from whoever offers the best cost/performance ratio for your own needs. All depending on how much time you spend on the phone and whether you make UK or international calls, calls to mobiles etc. And you can have several VoIP providers in paralle;, always picking the one that has the lowest cost for a particular destination.
 
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If you can't hear a noticeable difference then there's probably something in the path that doesn't do HD voice. When I had BT Digital Voice the call quality between the 'landline' and an EE mobile was impeccable.

As for the OPs aim to improve call quality from GPs etc. - it's unlikely to make any difference. As far as I know there is no widely used interconnect service for HD voice calls so you'll be getting the lowest quality all the time, and no guarantees that TDM isn't in the path somewhere.
 
Going off on a slight tangent and there maybe reasons why you can't, but have you considered using a mobile phone.

If you have a good signal to be able to use VoLTE or if not Wifi Calling you may find the quality of the call is good.

I have BT Digital Voice but for other reasons do all my calls via the mobile phone and at home it uses Wifi calling because we're in a poor signal area.

I find the call quality very good to other landlines. Call quality to other mobiles can vary but that could be due to signal conditions at the other end.

I have poor hearing and wear hearing aids. They are Bluetooth enabled so the call on my mobile comes through them and its very good, especially when there's a lot of background noise.
 
The essential difference between BT and most (all?) other ISPs is that BT's router has a built in DECT base station, and that's what their fancy handsets talk to. You can also pair your own handset to that base station and get HD functionality provided your handset supports it (eg a lot of Gigaset ones do, even if they were sold with a traditional base station).

Virgin doesn't seem to use DECT, instead they send an "adapter" (which is just an RJ11 to BT plug adapter, the sort of thing you can buy for 99p on ebay) and they require you to plug your existing phone into the router. There is no practical way to do "HD" with this method, just as you won't get "HD" if you plug a phone into the back of the BT router.

In theory the "over the top" voip solutions like Voipfone could support HD calls to mobiles/landlines assuming your IP phone supports it (many do) and provided the requisite plumbing has been done to allow "HD" to pass through. Again, use of an ATA would prevent this - must be an actual IP phone or IP enabled DECT base station.

Even if BT DV supports HD Voice, this does not guarantee that all calls will be HD end-to-end. They should be HD voice as long as it is between two BT DV subscribers, but once the call is between customers on different networks, there is no guarantee that they will get HD voice end-to-end.
It works when calling EE mobiles too (shock!) and there's no reason why it shouldn't work when calling any other mobile, just as you often get HD quality on calls between mobiles on two different networks.
 
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We are in a period of transition and even after December 2025 many consumers will be plugging in corded phones and cordless phone base units into routers or existing house wiring of various age and standards.

We also have companies that are still using G.729 or devices set to it. I have a personal rant regarding poor music on hold and talk radio shows that are clear indicators of that.

Yes, BT as far as I am aware, are the only provider offering an HD consumer offering. But as highlighted using an analogue socket or wiring will introduce analogue. With issues if wiring not up to standard. Those using Cordless phones will introduce further A/D conversions which are very likely to be G.711.

The large providers such as BT/EE, Sky. Vodafone, Virgin providing centrally provisioned router based voice are more likely to have dedicated routing to their VoIP infrastructure and provide the emergency services with more confidence of location.

Many providing VoIP do not appear to provide any routing information or state their standards which may include connectivity over the general internet. Whether its the provider or the device many are still G.711 (or worse G.729).

The more important point going forward that "Digital Voice" finally removes for the line circuit, attenuation of the line, high resistance faults, water ingress, cross talk, jelly crimps, aluminium etc. Calls may not necessarily be higher quality end to end but they should be a lot clearer.
 
The essential difference between BT and most (all?) other ISPs is that BT's router has a built in DECT base station, and that's what their fancy handsets talk to.
No need to get tied in to BT DV for that, a Fritzbox does exactly the same (and more). HD telephony included. and you can chose whicever VoIP provider(s) you want to use.
We also have companies that are still using G.729 or devices set to it.
Not sure who still uses G.729 but there are clearly better codecs around. Up to the end of 2016 you even had to pay royalty to use it.

Those using Cordless phones will introduce further A/D conversions which are very likely to be G.711.
DECT mandares G.726 and G.722 (i.e. HD voice), so if the VoIP provider supports HD voice, then there would be no transcoding involved from DECT to VoIP as long as DECT is integrated un the VoIP router (e.g. BT Home Hub or Fritzbox).
Again, use of an ATA would prevent this - must be an actual IP phone or IP enabled DECT base station.
Totally agree, if you use an ATA and plug in a DECT base station, then you get two (otherwise unneccesary) codecs in the voice path. Another reason why I consider ATAs to be a bodge rather than a solution.

Many providing VoIP do not appear to provide any routing information or state their standards which may include connectivity over the general internet. Whether its the provider or the device many are still G.711 (or worse G.729).
Most, if not all telecom operators use public internet to interconnect to other operators whether both in the UK and to destinations abroad, but given the massive bandwidth available, this should rarely affect call quality. After all, in a competitive market where a UK end user can can call Singapore or the US for for as little as 1p per minute, it is hardly surprising that the operators have to keep their costs down wherever possible.

As always, you can't have your cake and eat it.

Some providers do at least state what codecs they support but that only applies to the connection between the end user and the provider's media gateway, not the interconnect.
 
DECT mandares G.726 and G.722 (i.e. HD voice), so if the VoIP provider supports HD voice, then there would be no transcoding involved from DECT to VoIP as long as DECT is integrated un the VoIP router (e.g. BT Home Hub or Fritzbox).

Very interesting. So DECT is actually capable of higher quality audio encoding, even though it is an old standard dating back to the early 1990s, and most DECT phones are fairly LoFi rather than HiFi.


Would you happen to know if the DECT module in the BT Smart Hub 2 transmits radio waves continuously 24 hours a day, or can the continuous operation be switched off (transmitting only during calls), as it can with Gigaset DECT phones?

Gigaset phones have a setting (the ECO Mode Plus) which disables the wireless signal from being constantly transmitted 24 hours a day.

From the health perspective, I would prefer not to be bathed in wireless transmissions all day and night, given that my router is located in my bedroom (which also doubles as an office which I use during the day). Not that I am too worried about this, but as someone with a chronic inflammatory illness, it perhaps might be wise to minimise RF radiation.
 
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Very interesting. So DECT is actually capable of higher quality audio encoding, even though it is an old standard dating back to the early 1990s, and most DECT phones are fairly LoFi rather than HiFi.
DECT has been around since 1987 but has evolved quite a bit since then. HD Voice was brought in by ETSI in April 2007.
Would you happen to know if the DECT module in the BT Smart Hub 2 transmits radio waves continuously 24 hours a day, or can the continuous operation be switched off (transmitting only during calls), as it can with Gigaset DECT phones?
No idea what the BT Smart Hub does, but AVM Fritzbox (e.g. 7530) support Eco-DECT mode and you can set a time range for that as well (e.g. Eco DECT mode from 10pm to 7am, normal mode during daytime). BTW, the Fritzbox also allows WiFi scheduling, independently of Eco DECT scheduling.
 
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