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In digital electronics a codec is often essential. It is an abbreviation for compression/decompression. This is critical in audio circuits and specifically for voice and that leads to the abbreviation vocoder for voice codec, a double acronym if you will. Compression/decompression refers to the process of taking a high sample rate and reducing the amount of data for transmission and then reversing the process.
In discussing the analog to digital concept you might have considered that as the number of bits gets large enough, you get a very accurate representation of the analog and you are correct. One of the central issues of VoIP is how much data is needed and how good is it. This has been a central issue in voice compression, even before the Internet.