What is g.711?

G.711: A Deep Dive

G.711 is a narrowband speech codec standardized by the ITU-T in 1972. It's one of the earliest and most widely used codecs for VoIP (Voice over IP) and telephony due to its simplicity, low computational complexity, and decent voice quality. It's a waveform codec, meaning it attempts to reproduce the actual waveform of the speech signal.

Here's a breakdown of its key aspects:

• Coding Method: G.711 uses pulse-code modulation (PCM) with either μ-law (mu-law) or A-law companding. Companding, short for compressing-expanding, is used to reduce the dynamic range of the audio signal, improving the signal-to-noise ratio, particularly for low-amplitude signals.

• Variants: There are two primary variations of G.711:

  • μ-law (mu-law): Predominantly used in North America and Japan. For more information on this version, visit μ-law.
  • A-law: Predominantly used in Europe and the rest of the world. More information is available on A-law.

• Bitrate: G.711 operates at a fixed bitrate of 64 kbps. This is derived from sampling the audio signal at 8 kHz and using 8 bits per sample. Thus Bitrate becomes an important property.

• Sampling Rate: It uses an 8 kHz Sampling%20Rate.

• Payload Size: For VoIP applications, G.711 audio is typically packetized into payloads. Common payload sizes are 20ms (160 bytes) and 30ms (240 bytes).

• Advantages:

  • Low Complexity: Requires minimal processing power, making it suitable for devices with limited resources.
  • Low Latency: Introduces very little delay, crucial for real-time voice communication.
  • Good Voice Quality: Provides acceptable voice quality, especially for narrowband speech.
  • Wide Compatibility: Universally supported by virtually all VoIP systems and devices.

• Disadvantages:

  • High Bandwidth Consumption: 64 kbps is relatively high compared to more modern codecs.
  • Lower Quality than Modern Codecs: Doesn't perform as well as newer codecs, particularly at lower bitrates. It is still good enough though.
  • No Error Resilience: G.711 itself does not include any error correction or concealment mechanisms.

• Applications: G.711 remains widely used in:

  • VoIP (Voice over IP)
  • PSTN (Public Switched Telephone Network)
  • PBX (Private Branch Exchange) systems
  • Fax over IP (FoIP)
  • Audio conferencing

• Standardization: Defined in ITU-T Recommendation G.711. You can find the standard description under Standardization.