Telecoms glossary • H
HD voice
Twice the audio band for the same bandwidth. Most businesses already own the handsets and are still making narrowband calls.
What is HD voice?in VoIP and business telephony
1. HD voice is a call carried in a wider audio band than the old telephone network could manage. Wideband codecs, chiefly ITU-T G.722, reproduce 50 Hz to 7,000 Hz where a traditional line delivered 300 Hz to 3,400 Hz, which makes speech easier to follow and names and reference numbers easier to hear first time.
2. It costs nothing extra on the wire. G.722 carries the same 64 kbit/s payload as G.711, so an HD call and a standard call draw the same bandwidth. What changes is what the handsets at each end reproduce.
What the extra band actually does
The old 300 Hz to 3,400 Hz band was chosen to fit as many calls as possible onto copper, not to reproduce a voice faithfully. Wideband adds back the range at both ends of that window, and each end does a different job.
- Below 300 Hz
- The lower part of the voice, roughly 50 to 200 Hz, is what makes a speaker sound like a person in the room rather than a person on a phone. It carries almost no information and most of the impression of quality.
- Above 3,400 Hz
- This is where intelligibility lives. The consonants that distinguish s from f from th sit up here, which is why narrowband calls turn spelling a surname or reading a reference number into an exercise in phonetic alphabets.
- On a conference call
- Several people mixed into a narrowband channel blur into one another. The extra range is what lets a listener tell voices apart, which matters more on a six-person call than on a two-person one.
Fatigue is the effect people notice without naming it. Narrowband audio forces the listener to reconstruct missing detail for the length of the call, and a day of that is measurably more tiring than a day of wideband calls.
Why your HD handsets are probably making narrowband calls
HD voice is negotiated, not switched on. Both ends have to offer a wideband codec and every hop in between has to carry it, so most calls that could be wideband are not.
| Call type | Realistic result | Why |
|---|---|---|
| Extension to extension | Wideband | Both handsets are yours and the call never leaves the platform. This is where HD voice reliably happens. |
| Between your own branches | Wideband | A direct link between two sites on the same platform behaves like an internal call. |
| To a landline or mobile | Narrowband | The call is handed to the public network, which carries the narrowband band. South African mobile networks do run their own HD voice over LTE, but that is a separate wideband scheme and it does not survive the handover. |
| To another VoIP provider | Usually narrowband | Depends entirely on the interconnect between the two platforms. Worth asking about, and rarely advertised. |
Then there is the setting nobody checks. Plenty of accounts ship with G.722 absent from the extension codec profile, so HD-capable handsets negotiate G.711 with each other and the business never hears the difference it paid for.
Checking whether you actually have it
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Call a colleague, then call a mobile
Two internal calls back to back against one external call is the whole test. If the internal call sounds fuller, wideband is working and the outside world is the limit. If they sound identical, wideband is not being negotiated at all.
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Read the codec off the call
Most desk phones show the negotiated codec on a call statistics screen, and most provider portals record it against the call. Look for G.722 rather than trusting an ear.
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Check the extension profile, not the handset
Handsets from the mainstream vendors have supported G.722 for years. The missing piece is almost always the codec list on the platform side, which is a setting rather than a purchase.
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Look at what the audio comes out of
A wideband stream played through a cheap handset earpiece or a headset built for narrowband gives most of the benefit away at the last centimetre.
Worth asking, not worth paying extra for
Ask whether G.722 is enabled by default on your plan and whether it is available on entry-level packages. It should be a checkbox, and a provider charging a premium for wideband is charging for a codec that costs them the same 64 kbit/s as the one they already give you.
If most of your calls are to customers on the public network, temper the expectation. HD voice will improve your internal and inter-branch calls, which for a distributed team is most of the day, and will change nothing about the call to a client’s mobile.
About this entry
Definitions are written for South African business buyers and checked against primary sources – provider documentation, standards bodies and ICASA – not vendor marketing. Reviews are independent and sponsors are always disclosed. Read our editorial policy and scoring methodology.
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