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Application of Interpolation - Oversampling in CD Players

Module by: Phil Schniter

Application of Interpolation- Oversampling in CD Players

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.
m10444fig3.png
Figure 1
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.
m10444fig4.png
Figure 2

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