A VoIP codec decides how a voice is turned into data, how much bandwidth each call uses and how natural the other person sounds. Pick the wrong one and calls sound muffled, choppy or use far more of your internet line than they need to. This guide explains the four VoIP codecs you will meet most often in India, G.711, G.729, G.722 and Opus, and how to choose between them for office phones, branches and remote staff.
What is a VoIP codec?
A codec (coder-decoder) compresses voice into small packets for the network and turns them back into sound at the other end. Two things matter for business calls:
- Audio range. Narrowband codecs carry the same range as a traditional phone line. Wideband codecs carry more of the voice, so speech sounds clearer and closer to a face-to-face conversation. This is what phone makers call HD voice.
- Bitrate. The amount of data per second for the voice itself. On the network each call also carries packet headers, so the real bandwidth is higher than the codec bitrate.
Both phones on a call must agree on a codec. If they share none, the PBX has to convert between codecs, which costs processing power and can lower quality.
The four common codecs at a glance
| Codec | Audio | Codec bitrate | Typical use |
|---|---|---|---|
| G.711 (μ-law and A-law) | Narrowband | 64 kbps | Default for SIP trunks and PRI interconnects |
| G.729 | Narrowband | 8 kbps | Slow or costly links between sites |
| G.722 | Wideband (HD voice) | 64 kbps | Internal calls between IP phones on the office network |
| Opus | Narrowband to fullband | Variable, roughly 6 to 510 kbps | Softphones, browsers and modern IP phones |
G.711: the safe default
G.711 is uncompressed voice at 64 kbps and the codec every SIP device understands. It comes in two versions: μ-law (ulaw), used mainly in North America and Japan, and A-law (alaw), used in India, Europe and most other countries. Indian SIP trunks and PRI lines generally use A-law. G.711 sounds like a normal phone line and has no licensing or processing worries, so it is the right default for calls to and from the outside world.
G.729: low bandwidth
G.729 squeezes voice into 8 kbps, about one eighth of G.711. It is useful on small links between branches or over satellite and congested connections. The trade-offs are slightly lower quality, more sensitivity to packet loss, and more work for the PBX when it has to convert to other codecs. Use it only where bandwidth is the real problem.
G.722: HD voice inside the office
G.722 uses the same 64 kbps as G.711 but carries a wider audio range, so voices sound fuller and words like “fifteen” and “fifty” are easier to tell apart. It is ideal between IP phones on the office network, where bandwidth is not a concern. Calls to mobile and landline numbers are still narrowband because the telephone network is, but internal calls clearly improve.
Opus: flexible and modern
Opus adapts its bitrate and audio range to the network, from narrowband on a poor mobile connection to full-band audio on a good one, and handles packet loss well. It is common in softphones, browsers (WebRTC) and newer IP phones. The BitVoice B301 and B303 IP phones support both G.722 and Opus.
Which codecs does Voxdial IP PBX support?
Voxdial IP PBX supports G.711 (ulaw and alaw), G.722 and G.729 for voice, and T.38 for fax over IP. Codecs are managed in two places:
- System-wide. In the General SIP settings, operators tick the codecs to offer and drag them into order. The codec at the top is preferred.
- Per extension. Each extension has allowed and disallowed codecs, so a remote user on a weak connection can be limited to a low-bandwidth codec while desk phones use HD voice.
For fax, codec choice matters even more. Fax over a compressed voice codec usually fails, so use T.38 or G.711. See fax over IP with T.38.
How to choose codecs for your office
- Inside the office: put G.722 first on IP phones, then G.711 A-law. Calls between colleagues get HD voice.
- SIP trunks and PRI: use G.711 A-law unless your provider asks for something else. Converting a carrier’s G.711 into G.729 saves nothing on the carrier side.
- Branches on small links: allow G.729 on the branch extensions or inter-site trunk if bandwidth is tight; otherwise stay with G.711 or G.722.
- Remote and home workers: use a codec that copes with loss. Read VoIP call quality for remote agents for jitter and packet loss targets.
- Keep the list short. Offer only the codecs you need, in the right order, so phones do not settle on an unexpected choice.
Codec bandwidth: a quick sizing guide
As a rough rule, plan around 90 to 100 kbps per call in each direction for G.711 or G.722 once packet headers are included, and about 30 to 40 kbps for G.729. Multiply by the number of calls you expect at the busiest hour, and leave headroom for data traffic. If calls and computers share the same internet line, use quality of service (QoS) on your router to give voice priority.
Need help planning codecs and bandwidth for your offices? Talk to BitVoice.
FAQs
What is the best VoIP codec?
There is no single best codec. G.722 gives the clearest internal calls, G.711 A-law is the safest for SIP trunks in India, G.729 saves bandwidth on small links, and Opus suits softphones and changing networks.
What is the difference between G.711 and G.729?
G.711 is uncompressed voice at 64 kbps with the best narrowband quality. G.729 compresses voice to 8 kbps, using far less bandwidth at the cost of slightly lower quality and more sensitivity to packet loss.
Is G.722 the same as HD voice?
Yes, in practice. G.722 is a wideband codec, and most IP phones label wideband audio as HD voice.
Which codec should I use for fax over VoIP?
Use T.38, or G.711 if T.38 is not available end to end. Compressed codecs such as G.729 usually break fax transmissions.
