How voice is coded digitally for voip?

The digitization of analog voice signals is a must to transmit voice over the digital IP network. It can be done in several ways

• PCM (Pulse Code Modulation) is a simple technique of sampling the sound signal at a fixed rate (8000 times/second) and generate a number corresponding to each sample. It assumes no specific property of the signal. So it works reasonably well with all types of sounds.
• LPC (Liner Predictive Coding) assumes specific properties of human voice and uses a more complex algorithm to digitize and compress voice data. It works well for sending human utterances offering a low data rate but is not suitable for transmitting music or fax.
• SBC (Sub Band Coder) uses a different approach of representing sounds in terms of frequencies rather than sampling at regular intervals.
• Hybrid coders like the CELP (Code Excited Linear Prediction) use a mixture of the techniques to transmit sound of adequate quality.

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