The digital audio signal on a CD is a 44.1kHz 44.1 kHz sampled representation of a continuous signal with bandwidth 20kHz 20 kHz . With a standard ZOH-DAC, the analog reconstruction filter would have passband edge at 20kHz 20 kHz and stopband edge at 24.1kHz 24.1 kHz . (See Figure 1) With such a narrow transition band, this would be a difficult (and expensive) filter to build.

If digital interpolation is used prior to reconstruction, the effective sampling rate can be increased and the reconstruction filter's transition band can be made much wider, resulting in a much simpler (and cheaper) analog filter. Figure 2 illustrates the case of interpolation by 44. The reconstruction filter has passband edge at 20kHz 20 kHz and stopband edge at 156.4kHz 156.4 kHz , resulting in a much wider transition band and therefore an easier filter design.