In telecommunication, analog decoding is the portion of the digital-to-analog conversion process that generates an analog signal value from the digital signal that resulted from analog encoding .
For each digital value, a voltage is chosen and the output signal's voltage is adjusted to that new voltage. The next digital value then results in another voltage. The resulting signal is a step like signal with sudden transitions from one voltage to another. It looks much like a Bar graph . Due to these sudden transitions, the resulting analog signal has unwanted high frequency components.
Further action is required to filter and integrate these samples to obtain a continuous approximation of the original signal, because analog decoding does not smooth the signal.
There are many methods to do analog decoding. Note that the term itself does not in any way specify the resulting voltage range, nor if the relationship between the input digital values and the resulting analog voltages is linear or has some other relationship.
Source: from Federal Standard 1037C and from MIL-STD-188