## Waveform coding – A/D converters

The term waveform coding is applied to source encoding methods that seek to digitise the incoming analogue waveform, without making use of any information about its frequency content or source parameters, and thus achieve more efficient coding. This method is the most flexible source coding technique, able to accommodate any type of input waveform regardless of the generating source, and is typified by the analogue to digital converter.

| The A/D conversion process, often more grandly called pulse code modulation in many textbooks, usually involves regular sampling of the input signal level and then a conversion of this sampled value into a number representing the level. The accuracy of the representation is governed primarily by the resolution of the A/D converter – that is, how many data bits it uses to represent each measured value. Typical A/D converters use eight bits for telephony voice digitization, and 16 or 18 bits for HiFi music digitization. Some professional mixing desks use 24-bit converters! Most communications links will make use of the complementary digital to analogue (D/A) converter in order to restore the analogue waveform samples from the received data words.

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