Deep Dive into Codecs

What is an audio codec? An audio codec is a digital electronic device or a computer-based software capable of encoding or decoding an audio data stream. When it is a software audio codec it will, essentially, consists of an algorithm that codes and decodes an audio stream. A hardware, audio codec will refer to a device that encodes analog audio as digital signals and decodes digital back into analog.

In this article, we will discuss different types of voice codecs and fax codecs along with the basic difference between them.

Voice Codecs

1. G.711

There are two variants of the G.711 codec, namely g.711u and g.711a. The g.711u is typically used within Japan and North America. Whereas, g.711a is used by other countries in the world. Developed in 1972, it is part of the narrowband codecs. Having said that, the g.711 uses an 8 kHz sampling frequency that has a bit rate of 64 Kbit/s.

The 64 Kbit/s is the amount of bandwidth required per second through your internet connection for handling a single phone call. That said, the g.711 data is not compressed. Therefore, the bit rate of 64 Kbit/s is large compared to other codecs that make use of compression techniques for lowering the required bandwidth.

2. G.722

Released in 1988 as a wideband codec, g.722 tries to improve on the g.711 codec by increasing its sampling rate and compression. The g.722 codec uses a 16 kHz sampling frequency using 14 bits per sample. Because the codec starts with an uncompressed bit rate of 224 Kbit/s, it uses compression techniques to attain a bit rate of 64 Kbit/s.

3. G.729

Another mainstream VoIP codec that is used to transmit phone calls over the internet is g.729. Having said that, g.729 codec encodes the voice in frames. Each of the g.729 frames is ten milliseconds long and includes 80 audio samples. Also, the bit rate requirement for one direction for the g.729 codec is 8 Kbit/s. Because the g.729 offers higher compression capabilities, you are able to make more calls using the internet connection at once.

4. GSM

GSM stands for Global System for Mobile Communications. The bit rate of the gsm codec is 13 Kbit/s when using the GSM-FullRate or 6.5 Kbit/s when using GSM-HalfRate. However, it offers less speech quality as compared to modern standards.

Comparison of Voice Codecs

G.711 prioritizes sound quality but does not perform compression. Therefore, it requires more bandwidth as compared to other codecs such as G.729. Whereas, G.729 performs compression. Therefore, it requires lesser bandwidth as compared to other codecs such as G.711 and G.722 while transferring the call to the other side. However, the audio quality is much lesser as compared to G.711.

Fax Codecs

Similar to voice codecs, there are different types of fax codecs such as T.30 and T.38. T.30 codec dates before the arrival of the internet and was used for transmitting documents between devices over PSTN. However, the growing popularity of IP meant that a new codec was required. On VoIP.ms T.38 codec is used to transfer documents over the internet without a phone line, learn more about its uses here: https://wiki.voip.ms/article/Fax_over_IP_(FoIP)_using_T.38_Protocol

VoIP.ms supports three different types of voice codecs – g.711u, g.729a, and gsm. In addition to this, VoIP.ms also supports T.38 codec, thus allowing you to send fax over internet protocol.