Digital-to-analog conversion (used in playback) is the exact oppo- site of the analog-to digital conversion process and is illustrated in Figure 21.
In digital-to-analog conversion, the PCM bitstream is converted at the sampling frequency to a continuously changing series of quantization levels which are individual "steps" of discrete voltage equal to the quantization levels in the analog-to-digital process. The shape of this continuously changing stream of quantization levels approximates the shape of the original wave. This is shown in the top half of Figure 21. This signal is then passed through a low-pass filter, which removes the digital "switching noise." The end result, shown in the bottom half of Figure 21 is an analog out- put signal whose waveshape is a very close approximation of the original analog input signal.
Figure 21. Digital-to-Analog
