1.3 Application of interpolation - oversampling in cd players

Application of interpolation- oversampling in cd players

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

If digital interpolation is used prior to reconstruction, the effective sampling rate can be increased and thereconstruction filter's transition band can be made much wider, resulting in a much simpler (and cheaper) analogfilter. illustrates the case of interpolation by $4$ . The reconstruction filter has passband edge at $20\mathrm{kHz}$ and stopband edge at $156.4\mathrm{kHz}$ , resulting in a much wider transition band and therefore an easier filter design.