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16. What is a CODEC? |
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A codec, which stands for coder-decoder, converts an audio signal into a compressed digital form for transmission and then back into an uncompressed audio signal for replay.
Codecs accomplish the conversion by sampling the audio signal several thousand times per second. For instance, a G.711 codec samples the audio 64,000 times a second and converts each tiny sample into digitised data and compresses it for transmission. When the 64,000 samples are reassembled, the pieces of audio missing between each sample are so small that to the human ear it sounds like one continuous second of audio signal. There are different sampling rates in VoIP depending on the codec being used:
• 64,000 times per second
• 32,000 times per second
• 8,000 times per second
A G.729A codec has a sampling rate of 8,000 times per second and is the most commonly used codec in VoIP, and is a compromised balance between sound quality and efficiency of bandwidth.
Codecs generally provide a compression capability to save network bandwidth. Some codecs also support silence suppression, where silence is not encoded or transmitted.
Some of the common CoDecs which are used in the industry are G711, G712, G723, G726, G727, G728 and G729. |
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