just what is call quality, anyway? voice quality terminology breakdown

A woman stands against a wall talking on a smartphone.

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illumy 3.0 will have the industry’s best voice quality: for both on-net calls between illumy users and off-net calls to ordinary phone numbers.

Our secret sauce is state-of-the-art audio tech that runs on our own powerful servers. This tech stack not only converts analog voice signals into bits and bytes — it automatically applies enhancements like echo cancellation and background noise cancellation.

And, because we have so much computing horsepower at our disposal, illumy calls will sample more of the audio spectrum. All of these things mean vastly improved call quality compared to what you’re used to.

Here, we’ve collected some key voice quality terms to get you up to speed with what’s coming in illumy 3.0.

Audio spectrum

The audio spectrum is the range of sounds that the human ear can hear. The average person can hear from 20Hz to 20,000Hz.

The average dog, meanwhile, can hear sounds up to 65,000Hz.

While illumy 3.0 won’t give you audio in the dog range, it does use much more of the audio spectrum than other carriers — making your illumy calls sound much more “real.”

You won’t be in the same room as the other person, but it will sound like it.


Bitrate is a measure of data emitted over a period of time.

Typical audio codecs use a fixed bitrate that assumes a pretty low level of data transfer, generally 64K (64,000 bits per second).

The codec powering illumy calls, on the other hand, will be rate adaptive. That means that if you have faster data speeds at your disposal, we’ll ramp up the bitrate to provide better call quality. On slow networks, we can dial it down to preserve stability.

All of this happens in the backend, so there’s nothing you need to do — other than enjoy great-sounding calls.


A codec is the software that translates an analog audio waveform to a digital packet. “Codec” is made up from the words “coder” and “decoder.”

The codec used by illumy voice, Opus, is one of the most advanced audio codecs in existence. It allows for a lot of flexibility — scaling back to narrowband quality when bandwidth is limited or super-wideband quality when more bandwidth is available.

(For definitions of narrowband and wideband, keep reading.)

HD Voice

HD Voice is actually just a marketing term. It refers to any voice technology that sounds better than narrowband.

Because there’s no standard definition for HD Voice, not every “HD” call will sound the same. And the truth is, most carriers don’t even offer HD quality — even on landline calls.

illumy voice will be the highest-def “HD” you can get in a calling app. It won’t reach the entire audio spectrum, but it will get a lot closer than any call you’ve heard before.


Morphemes are the edges of sounds. They’re what distinguishes how one sound stops so another one can begin. And as the basic building blocks of spoken language, morphemes are how voice gets turned into meaning.

In illumy’s tech stack, we deploy custom media libraries to tweak the morphemes you hear for the highest possible clarity.


MOS, short for Mean Opinion Score, is a rating system used to judge call quality.

MOS uses a 0-to-5 scale to gauge how a call compares to the original analog sound. A score of 5 would be comparable to having the other person right next to you.

In the telco world, “carrier-grade” MOS means a score of 2.5 and above. In other words, typical telco carriers are ok with your calls sounding nothing like the real-world equivalent.

(The scale is logarithmic, so 2.5 doesn’t mean “half as good” — it’s actually way worse.)

At illumy, we plan to do a lot better. HD Voice usually means a MOS of 3.8 to 4.7, and we will be at the high end of that range.


Narrowband refers to the limited frequency range that is typical in the telco industry.

Conventionally, narrowband means frequencies between 300Hz and 3,400Hz. This is known as the voiceband.

The most common audio codec, G.711, only encodes sounds within this range. That’s good for telco carriers, because it lets them jam more users on their networks. But it’s bad for you. The human voice is much wider than narrowband, so there’s a lot you are going to miss on a normal phone call.


Wideband is a broad term, because it covers all audio sampling outside the narrowband spectrum range.

Some codecs capture more of the high end. Some dip down into the lower ranges of the frequency spectrum. illumy’s codec, Opus, can cover almost the entire audio spectrum with what’s known as super wideband.

With super-wideband Opus powering illumy VoIP, all of your calls will sound pretty super. And remember, Opus is rate-adaptive. So if your data speeds drop, your calls won’t. We just scale the quality back to narrowband levels.

Photo by Arnaud STECKLE on Unsplash.

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