Previous article, we discussed about sampling of audio. Now having the audio signal represented as a sequence of samples, the next step is to compress it to reduce the consumption of network bandwidth required to transmit the speech to the receiving party.
The compression and decompression is handled by special algorithms we call codecs (COder-DECoder). Let's have a look at some popular codecs that are being used in Voice over IP. All the codecs we list here expect the input to be audio sampled at 8 kHz with 16-bit samples.
In the text below, we will mention the MOS of the codecs. MOS stands for "Mean Opinion Score". MOS measures the perceived quality of audio after it has been compresses by the particular codec, transmitted, and decompressed. The score is assigned by a group of listeners using the procedure specified in ITU-T standards P.800 and P.830. The interpretation of individual MOS values is as follows:
5 => Excellent
4 => Good
3 => Fair
2 => Poor
1 => Bad
G.711 MOS value = 4.2
G.729 MOS value is 4.0
G.723.1 variant 1 has MOS 3.9 and variant 2 has MOS 3.5
GSM 06.10 MOS is 3.7
references:
http://toncar.cz/Tutorials/VoIP/VoIP_Basics_Overview_of_Audio_Codecs.html
The compression and decompression is handled by special algorithms we call codecs (COder-DECoder). Let's have a look at some popular codecs that are being used in Voice over IP. All the codecs we list here expect the input to be audio sampled at 8 kHz with 16-bit samples.
In the text below, we will mention the MOS of the codecs. MOS stands for "Mean Opinion Score". MOS measures the perceived quality of audio after it has been compresses by the particular codec, transmitted, and decompressed. The score is assigned by a group of listeners using the procedure specified in ITU-T standards P.800 and P.830. The interpretation of individual MOS values is as follows:
5 => Excellent
4 => Good
3 => Fair
2 => Poor
1 => Bad
G.711 MOS value = 4.2
G.729 MOS value is 4.0
G.723.1 variant 1 has MOS 3.9 and variant 2 has MOS 3.5
GSM 06.10 MOS is 3.7
references:
http://toncar.cz/Tutorials/VoIP/VoIP_Basics_Overview_of_Audio_Codecs.html
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