Codec
A codec (coder-decoder) is the method a VoIP system uses to turn voice into data for sending over a network and back into sound, balancing audio quality against bandwidth.
How codecs work
Both sides of a call agree on a codec when the call starts. Some codecs keep the full sound and need more bandwidth; others compress it to save bandwidth at some cost in quality. Wideband (HD voice) codecs capture a wider range of the voice and sound clearer than traditional phone calls.
Common codecs
| Codec | What it is |
|---|---|
| OPUS | Modern wideband codec that adapts to network conditions |
| G.722 | Wideband (HD voice) codec used by many IP phones |
| G.711 (PCMU, PCMA) | Uncompressed standard phone-quality codec; PCMU is used in North America and Japan, PCMA elsewhere |
| G.729 | Compressed codec for low-bandwidth connections |
| GSM | Older compressed codec from mobile networks |
telephone-event is not a voice codec: it carries keypad presses (DTMF) separately from the audio, so menus recognise them reliably.
Codecs in phone.systems™
phone.systems™ SIP accounts support OPUS, G722, PCMU, PCMA, G729, GSM and telephone-event. For BYOC termination gateways you set the codec priority order, so the preferred codec is offered first. For connecting a desk phone, see IP phone.