Category:Codec

From Snom User Wiki

Overview

The word codec is a portmanteau of 'compressor-decompressor' or, more commonly, 'coder-decoder'....A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. Codecs are used in videoconferencing, streaming media and video editing applications.

As with conventional telephony, with VoIP the speech is initially captured in analog form with a microphone. This analog information is then transferred into a digital format by a converter and changed through codecs into corresponding audio-binary formats. Depending on the codec used, the data can be compressed to differing extents in this process.

Most codecs use a procedure through which - similar to MP3 files - information not important for the human ear is omitted. This reduces the amount of data and thus reduces the bandwidth required for transfer. However, if too much information is omitted, the speech quality will suffer.

The different codec procedures master the audio compression with different levels of efficiency. Some are specifically designed to achieve a low bandwidth at any cost. Depending on the codec, therefore, the necessary bandwidth and the speech quality will vary. In order for the data also to be converted correctly back into speech after the transport, the receiver must use the same codec as the sender.

Codec Name	Coding Type	Frequency (Hz)	Bandwith (kbps)	Value	snom3xx/820/710	snom720/760	snom821/870	snomMP
G.722	SB-ADPCM	50-7000 (wideband)	64	g722
G.711ulaw	PCM	200-3500 (narrowband)	64	pcmu
G.711alaw	PCM	200-3500 (narrowband)	64	pcma
GSM-FR	RPE-LTP	200-3500 (narrowband)	13	gsm
G.723.1	MPC-MLQ	200-3500 (narrowband)	6.3	g723
G.723.1	ACELP	200-3500 (narrowband)	5.3	g723
G.726-16	ADPCM	200-3500 (narrowband)	16	g726-16
G.726-24	ADPCM	200-3500 (narrowband)	24	g726-24
G.726-32	ADPCM	200-3500 (narrowband)	32	g726-32
G.726-40	ADPCM	200-3500 (narrowband)	40	g726-40
AAL2-G.726-16	ADPCM	200-3500 (narrowband)	16	aal2-g726-16
AAL2-G.726-24	ADPCM	200-3500 (narrowband)	24	aal2-g726-24
AAL2-G.726-32	ADPCM	200-3500 (narrowband)	32	aal2-g726-32
AAL2-G.726-40	ADPCM	200-3500 (narrowband)	40	aal2-g726-40
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	6.6	amrwb-0
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	8.75	amrwb-1
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	12.65	amrwb-2
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	14.25	amrwb-3
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	15.85	amrwb-4
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	18.25	amrwb-5
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	19.85	amrwb-6
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	23.05	amrwb-7
AMR-WB (G.722.2)	ACELP	50-7000 (wideband)	23.85	amrwb-8
G.729A	CS-ACELP	200-3500 (narrowband)	8	g729-annexb=no
G.729AB	CS-ACELP	200-3500 (narrowband)	8	g729
				cn
				telephone-event

AMR-WB is not included in the standard FW. Please contact your snom Sales representative for further information.

cn is only supported from FW version 8.7.3 onwards

720/760 do not support the following paket sizes with the following codecs - G722: 40, 60 ms; G711: 60 ms; g726 (all variants): 40, 60 ms; AAL2*: 60 ms;