VoIP Codecs

A codec (Coder/Decoder) converts analog signals to a digital bitstream, and another identical codec at the far end of the communication converts the digital bitstream back into an analog signal.

In the VoIP world, codecs are used to encode voice for transmission across IP networks.

Codecs for VoIP use are also referred to as vocoders, for “voice encoders”.

Codecs generally provide a compression capability to save network bandwidth. Some codecs also support silence suppression, where silence is not encoded or transmitted.

Codec	Algorithm	Bit Rate (Kbps)	Comments
ITU G.711	PCM (Pulse Code Modulation)	64	G.711 with mu-law used in North America and Japan, while G.711 with A-law used in the rest of the world.
ITU G.722	SBADPCM (Sub-Band Adaptive Differential Pulse Code Modulation)	48, 56 and 64
ITU G.723	Multi-rate Coder	5.3 and 6.4
ITU G.726	ADPCM (Adaptive Differential Pulse Code Modulation)	16, 24, 32, and 40
ITU G.727	Variable-Rate ADPCM	16-40
ITU G.728	LD-CELP (Low-Delay Code Excited Linear Prediction)	16
ITU G.729	CS-ACELP (Conjugate Structure Algebraic-Code Excited Linear Prediction)	8
ILBC	Internet Low Bitrate Codec	13.33 and 15.20
Speex	CELP (Code Excited Linear Prediction)	2.15-44.2	Part of the GNU Project and available under the Xiph.org variant of the BSD license
GSM – Full Rate	RPE-LTP (Regular Pulse Excitation Long-Term Prediction)	13
GSM – Enhanced Full Rate	ACELP (Algebraic Code Excited Linear Prediction)	12.2
GSM – Half Rate	CELP-VSELP (Code Excited Linear Prediction – Vector Sum Excited Linear Prediction)	11.4
DoD FS-1016	CELP (Code Excited Linear Prediction)	4.8