What is HD voice (wideband), and when do you hear it?

Definition: what is a "band"

Every sound is a vibration at a certain frequency: low sounds have a low frequency, high sounds a high frequency. The human ear hears roughly from 20 to 20,000 Hz. Our speech uses a large part of that range.

The classic telephone carried only a narrow band: about 300 to 3,400 Hz. That is enough to understand words, which is why the standard lasted for decades. But many of the sounds that tell consonants apart, and the natural tone of the voice, were simply cut off.

HD voice widens the band, usually to a range of about 50 to 7,000 Hz. The difference is heard right away: the voice is less "metallic," it takes less effort to understand, and there is less "what did you say?"

Comparison: narrowband, wideband, and beyond

Important to understand: "HD" is not a single codec but a description of the width of the band that is carried. Several different codecs provide it.

G.722 and Opus — the two names you will meet

• G.722 — an established codec (standardized in 1988), supported by almost every modern desktop IP phone. It uses about the same bandwidth as G.711, so it doesn't require a better connection. It is the common HD codec between desktop phones.
• Opus — a newer, very flexible codec: it adapts to the available bandwidth and copes well with packet loss. It is common in softphones, apps, and browsers.

There are other wideband codecs, but these are the two most common. For more on codecs in general, see Codec.

A small technical detail that is sometimes confusing: in the settings of many phones, G.722 appears as an "8,000 Hz" codec, even though it actually samples 16,000 times a second. This is a historical error in the standard, kept so as not to break compatibility between devices. For the user, it changes nothing.

Opus, by contrast, can switch between narrowband, wideband, and even full band in the middle of a call, depending on the state of the network. When the connection is good, it improves the quality; when the connection weakens, it lowers the data rate instead of letting the call break up.

Why not every call is HD

HD voice works only when the whole chain supports it. If one link doesn't, the call drops to narrowband.

1. Both devices need to support the same wideband codec.
2. The PBX needs to allow it and not convert to a narrow codec along the way.
3. Everything in between — if the call goes out to the public telephone network, it usually passes through in narrowband, and then even the best device will sound like a "phone voice."
4. The headset or speaker — a cheap speaker or an old headset won't reproduce the high frequencies.

That is why the difference is felt mainly in calls between extensions inside the organization — between the secretary and the treasurer, between one branch and another — and less in calls with outside customers.

There is also an in-between case: the PBX receives the voice in HD from one side and converts it to narrowband for the other side. This conversion is called "transcoding." It lets each party speak in its own codec, but the quality is set by the weakest link in the chain.

What about mobile?

Newer cellular networks have their own HD voice, for example in VoLTE calls, when both sides are on the same network and support it. But when the call passes between networks, or arrives from a PBX through the public network, it is usually converted along the way.

In other words: your mobile phone may show an HD sign on a call with a friend, and not on a call with the office. That doesn't mean something is broken — only that the call passed through a narrowband link.

You can also get HD on a softphone on a mobile phone, as long as the app supports a wideband codec and the call is to another extension in the organization. That way an employee who is out, with an app and a good connection, can talk to the office at better quality than a regular cellular call.

How much bandwidth it takes

A common question is whether HD voice will "burden" the internet. The answer in most cases: not by much.

In other words, anyone who works with G.711 today can switch to G.722 without changing anything in the connection. Only on very narrow connections, where a compressed codec was chosen in the first place, do you need to think about it. See Bandwidth.

Who benefits most

• Service centers — a representative who hears clearly gets less tired at the end of a day of calls, and asks for details to be repeated less often.
• Conferences — in a call with several participants, clear sound helps you tell who is speaking. See Conference phone.
• Classes and lectures by phone — the voice sounds more natural, and listening for a long time is less tiring.
• Names and numbers — the difference between "sixty" and "seventy," or between similar names, is clearer.
• Older people and the hard of hearing — every extra sound that is preserved can help them understand words without guessing.

On the other hand, in short calls of "yes, no, thanks," it is hard to feel a difference. The advantage grows the longer the call is, and the more names, numbers, and details it has that need to be caught correctly the first time.

How to tell that a call is really HD

There are several ways to check, from the simplest to the most precise:

• An indicator on the display — many phones show an "HD" symbol during a wideband call.
• Call details on the phone — on many devices, pressing "Status" or "Details" during a call shows the codec in use.
• The ear test — say "s" and "sh," or "p" and "t," in turn. In narrowband they sound alike; in HD the difference is clear.

If two extensions that support HD talk in narrowband, check the codec order on the phones. The phone offers codecs in order of priority, and if G.711 comes before G.722, the call may be set up on it.

Common myths

• "HD requires extra-fast internet" — No. G.722 uses about the same as a regular codec.
• "If the phone supports HD, all calls will be HD" — No. The other side, and the whole path, need to support it too.
• "HD will fix choppy audio" — No. Choppy audio comes from network problems, such as packet loss or jitter. A good codec doesn't fix a bad network. See Latency and jitter.
• "The headset doesn't matter" — It matters a lot. A headset that doesn't carry high frequencies cancels the advantage. See Headsets.

And one last myth: "HD is just marketing." The difference is measurable and audible. In call quality tests, wideband calls usually get a higher score than narrowband calls under the same network conditions. See MOS score.

An example from the field

At the Talmud Torah "Bnei Chaim" (a made-up name), the secretary and the principal spoke on the phone between two branches several times a day. The principal complained that he "always has to ask for the students' names to be repeated."

Both phones supported G.722, but on one of them G.711 was set first in the codec list. After the order was changed, calls between the branches moved to wideband. Calls to parents outside stayed at regular phone quality — because they go out to the public network — but the internal calls sounded completely different.

A little history: why the phone stayed narrow for so long

The phone's narrow band wasn't chosen because no one knew how to do better. It was chosen because it was cheap and sufficient. In a world of copper wires and switchboards, every voice channel "took up space" on the network, and with a narrow band you could carry more calls over the same cables.

When networks went digital, the format of 8,000 samples per second was set — exactly what is needed to carry sounds up to about 4,000 Hz. That format, G.711, is still the common language of telephone networks around the world.

The move to HD came with the internet: when voice travels in packets, there is no reason to stick to the limits of the old cables. But as long as a call has to pass through the public network, the old format remains the common denominator.

How to get the most out of HD voice

1. Phones that support G.722 — most modern desktop phones do.
2. The right codec order — G.722 before G.711 in the list.
3. A network cable, not Wi-Fi — for a desktop phone, so the voice arrives intact.
4. A good headset — especially in call centers, where people talk for hours.
5. A quiet room — HD also carries background noise more clearly: an air conditioner, a keyboard, a conversation in the next room. A microphone close to the mouth helps.

The last item surprises people: higher-quality voice is also more honest voice. What used to get lost in narrowband is now heard.