Codecs are generally understood to be various mathematical models used to digitally encode (and compress) analog audio information. Many of these models take into account the human brain’s ability to form an impression from incomplete information. We’ve all seen optical illusions; likewise, voice-compression algorithms take advantage of our tendency to interpret what we believe we should hear, rather than what we actually hear.^[209] The purpose of the various encoding algorithms is to strike a balance between efficiency and quality.^[210]

Originally, the term codec referred to a COder/DECoder: a device that converts between analog and digital. Now, the term seems to relate more to COmpression/DECompression.

Before we dig into the individual codecs, take a look at Table B.1, “Codec quick reference”—it’s a quick reference that you may want to refer back to.

Table B.1. Codec quick reference

Codec	Data bitrate (Kbps)	License required?
G.711	64 Kbps	No
G.726	16, 24, 32, or 40 Kbps	No
G.729A	8 Kbps	Yes (no for pass-through)
GSM	13 Kbps	No
iLBC	13.3 Kbps (30-ms frames) or 15.2 Kbps (20-ms frames)	No
Speex	Variable (between 2.15 and 22.4 Kbps)	No
G.722	64 Kbps	No

G.711 is the fundamental codec of the PSTN. In fact, if someone refers to PCM (discussed in Appendix A, Understanding Telephony) with respect to a telephone network, you are allowed to think of G.711. Two companding methods are used: μlaw in North America and alaw in the rest of the world. Either one delivers an 8-bit word transmitted 8,000 times per second. If you do the math, you will see that this requires 64,000 bits to be transmitted per second.

Cd asterisk make clean make menuselect This will bring up a menu selection for Asterisk. Select item #4 Codec Translators. Scroll to codecilbc and check that box. Save (s) the selection and exit. Then do: make This re-compiles Asterisk and will take a little while. When it is done do: make install.
A final note about codec selection. There are quite a few codecs in Asterisk to choose from, but ulaw, alaw, GSM and ADPCM should only be used, the rest of the standard Asterisk codecs (speex, ilbc, lpc10, etc) should be avoided. The ulaw and alaw codecs have the best audio quality, followed.

Many people will tell you that G.711 is an uncompressed codec. This is not exactly true, as companding is considered a form of compression. What is true is that G.711 is the base codec from which all of the others are derived.

Asterisk 1.6.2 - Asterisk 1.8. The addition of G.719 pass-through support. RESAMPLE Codec: Asterisk 1.4 - Asterisk 1.6.0. Added a new codec translation module, codecresample, which re-samples signed linear audio between 8 kHz and 16 kHz to help support wideband codecs. ILBC Codec: Asterisk 1.4 - Asterisk 1.6.0.

G.711 imposes minimal (almost zero) load on the CPU.

This codec has been around for some time (it used to be G.721, which is now obsolete), and it is one of the original compressed codecs. It is also known as Adaptive Differential Pulse-Code Modulation (ADPCM), and it can run at several bitrates. The most common rates are 16 Kbps, 24 Kbps, and 32 Kbps. As of this writing, Asterisk supports only the ADPCM-32 rate, which is far and away the most popular rate for this codec.

G.726 offers nearly identical quality to G.711, but it uses only half the bandwidth. This is possible because rather than sending the result of the quantization measurement, it sends only enough information to describe the difference between the current sample and the previous one. G.726 fell from favor in the 1990s due to its inability to carry modem and fax signals, but because of its bandwidth/CPU performance ratio it is now making a comeback. G.726 is especially attractive because it does not require a lot of computational work from the system.

Install ilbc codec asterisk definition windows 10

Considering how little bandwidth it uses, G.729A delivers impressive sound quality. It does this through the use of Conjugate-Structure Algebraic-Code-Excited Linear Prediction (CS-ACELP).^[211] Because of patents, you can’t use G.729A without paying a licensing fee; however, it is extremely popular and is well supported on many different phones and systems.

Install ilbc codec asterisk definition free

To achieve its impressive compression ratio, this codec requires an equally impressive amount of effort from the CPU. In an Asterisk system, the use of heavily compressed codecs will quickly bog down the CPU.

G.729A uses 8 Kbps of bandwidth.

The Global System for Mobile Communications (GSM) codec is the darling of Asterisk. This codec does not come encumbered with a licensing requirement the way that G.729A does, and it offers outstanding performance with respect to the demand it places on the CPU. The sound quality is generally considered to be of a lesser grade than that produced by G.729A, but much of this comes down to personal opinion; be sure to try it out. GSM operates at 13 Kbps.

The Internet Low Bitrate Codec (iLBC) provides an attractive mix of low bandwidth usage and quality, and it is especially well suited to sustaining reasonable quality on lossy network links.

Naturally, Asterisk supports it (and support elsewhere is growing), but it is not as popular as the ITU codecs, and thus may not be compatible with common IP telephones and commercial VoIP systems. IETF RFCs 3951 and 3952 have been published in support of iLBC, and iLBC is on the IETF standards track.

Install ilbc codec asterisk definition online

Because iLBC uses complex algorithms to achieve its high levels of compression, it has a fairly high CPU cost in Asterisk.

While you are allowed to use iLBC without paying royalty fees, the holder of the iLBC patent, Global IP Sound (GIPS), wants to know whenever you use it in a commercial application. The way you do that is by downloading and printing a copy of the iLBC license, signing it, and returning it to GIPS. If you want to read about iLBC and its license, you can do so at http://www.ilbcfreeware.org.

iLBC operates at 13.3 Kbps (30-ms frames) and 15.2 Kbps (20-ms frames).

Speex is a variable bitrate (VBR) codec, which means that it is able to dynamically modify its bitrate to respond to changing network conditions. It is offered in both narrowband and wideband versions, depending on whether you want telephone quality or better.

Speex is a totally free codec, licensed under the Xiph.org variant of the BSD license.

An Internet draft for Speex is available, and more information about Speex can be found at its home page (http://www.speex.org).

Speex can operate at anywhere from 2.15 to 22.4 Kbps, due to its variable bitrate.

G.722 is an ITU-T standard codec that was approved in 1988. The G.722 codec produces a much higher-quality voice in the same space as G.711 (64 Kbps) and is starting to become popular among VoIP device manufacturers. The pat

Install Ilbc Codec Asterisk Definition