Glossary · G.711
What is G.711?
G.711 is the ITU-T standard narrowband audio codec that encodes voice as uncompressed pulse-code modulation (PCM) at 64 kbps, delivering “toll-quality” telephone audio. First published in 1972 and titled Pulse code modulation (PCM) of voice frequencies, it samples speech at 8 kHz across the 300 Hz to 3.4 kHz band and remains the baseline codec that virtually every PSTN and VoIP endpoint supports.
How G.711 works
G.711 takes an analog voice signal, samples it 8,000 times per second, and quantizes each sample to 8 bits — producing the fixed 64 kbps bitstream (8,000 × 8). Because the audio is companded rather than truly compressed, there is almost no encoding delay and negligible CPU cost.
Companding maps a wider linear PCM sample down to a logarithmic 8-bit value, preserving more detail in quiet passages where the human ear is most sensitive. This is why G.711 sounds clean despite its simplicity.
A-law vs. mu-law
G.711 ships in two companding variants. They are not interoperable on the same call leg, so endpoints must negotiate a common one — typically resolved at the gateway between regions.
| Variant | Region | Encodes from | Notes |
|---|---|---|---|
| mu-law (PCMU) | North America, Japan | 14-bit linear PCM | More resolution on louder signals |
| A-law (PCMA) | Most of the rest of the world | 13-bit linear PCM | More quantization levels at low signal levels |
Both produce the same 64 kbps, 8 kHz narrowband output and the same toll-quality result; only the logarithmic mapping differs.
Key facts at a glance
| Property | Value |
|---|---|
| Standard | ITU-T Recommendation G.711 (1972) |
| Type | Narrowband PCM (uncompressed) |
| Sampling rate | 8 kHz |
| Frequency range | 300 Hz – 3.4 kHz |
| Bitrate | 64 kbps |
| Sample size | 8 bits (companded) |
| MOS (quality) | ~4.2 / 5 (toll quality) |
| RTP payload types | 0 (PCMU), 8 (PCMA) |
The roughly 4.2 Mean Opinion Score is the practical ceiling for narrowband telephony — clear and natural, but missing the low and high frequencies that wideband codecs add.
Where G.711 fits in business phone and VoIP
Because it is universally supported and computationally trivial, G.711 is the safe fallback codec on nearly every deployment:
- PSTN gateways: the public phone network is narrowband, so calls crossing to the PSTN are transcoded to G.711.
- SIP interconnects: carriers that do not carry wideband negotiate G.711 as the lowest common denominator.
- High-bandwidth LANs: where bandwidth is plentiful, G.711’s lack of compression means zero quality loss and no licensing cost.
- Fax and tone reliability: uncompressed PCM passes DTMF and fax tones more faithfully than compressed codecs.
The trade-off is bandwidth: at 64 kbps plus RTP, IP, and Ethernet overhead, a single G.711 stream consumes roughly 87 kbps per direction — far more than compressed codecs like G.729, which is why low-bandwidth links often prefer compression.
G.711 vs. G.722
G.711 and G.722 run at the identical 64 kbps but cover very different frequency ranges. G.722 is the wideband upgrade that delivers “HD Voice” at no extra bitrate when both endpoints support it.
| Codec | Class | Frequency range | Bitrate |
|---|---|---|---|
| G.711 | Narrowband | 300 Hz – 3.4 kHz | 64 kbps |
| G.722 | Wideband | 50 Hz – 7 kHz | 64 kbps |
On modern on-net calls, endpoints prefer G.722; G.711 takes over the moment the path touches the narrowband PSTN.
G.711 frequently asked questions
What does G.711 mean?
G.711 is the ITU-T Recommendation number for a narrowband audio codec that encodes voice as uncompressed pulse-code modulation (PCM) at 64 kbps. Published in 1972, it is the baseline ‘toll-quality’ codec supported by virtually every PSTN and VoIP phone, sampling audio at 8 kHz across the 300 Hz to 3.4 kHz range.
What is the difference between A-law and mu-law G.711?
Both are companding variants of G.711 that produce the same 64 kbps narrowband audio.
mu-law (RTP payload PCMU) is used in North America and Japan and encodes from 14-bit linear PCM. A-law (PCMA) is used across most of the rest of the world and encodes from 13-bit linear PCM. They are not interoperable, so a gateway transcodes between them when calls cross regions.
What is the bitrate of G.711?
G.711 operates at a fixed 64 kbps, derived from sampling voice 8,000 times per second at 8 bits per sample. Because the audio is companded rather than compressed, the bitrate never varies. With RTP, IP, and Ethernet overhead, a real G.711 call stream consumes roughly 87 kbps per direction on the network.
What is the difference between G.711 and G.722?
Both run at 64 kbps, but G.711 is narrowband (300 Hz to 3.4 kHz) while G.722 is wideband (50 Hz to 7 kHz). G.722 delivers the clearer ‘HD Voice’ experience at the same bitrate when both endpoints support it. G.711 remains the fallback whenever a call leg touches the narrowband public phone network.
Is G.711 still used today?
Yes. G.711 is the most widely supported voice codec in existence and serves as the universal fallback. Calls bridging to the PSTN are transcoded to G.711 because the public phone network is narrowband, and it is preferred on high-bandwidth LANs where its lack of compression means zero quality loss and no licensing cost.
See how DialPhone fits
DialPhone’s business phone negotiates the best available codec on each call leg — preferring wideband G.722 for HD Voice on supported endpoints and falling back to universally compatible G.711 at PSTN gateways — so every call connects cleanly regardless of the far end’s capabilities.