Frequency-domain illustration of interpolation

Demonstrates the effects of upsampling a signal and filtering it.

Do This:

  1. The black plots are the signal to be upsampled. Move the Visible slider to 2. The red plots are the upsampled versions. Note every other sample is zero. Also note the width of the spectrum has be cut in half and there are copies of the spectrum.
  2. Set the Expansion factor to 3. What happens in the frequency domain?
  3. Try other expansion factors. What happens?
  4. Slide the Visible slider to 3. The green is the filtered version of the upsampled signal. Notice the higher frequencies are missing. Also notice in the time domain the zero values have been filled in.
  5. Why is the peak of the green signal delayed from the red signal? Hint: Try changing the filter order.
  6. Try adjusting the fliter cutoff frequency and the Expansion factor. What happens?

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Oppenheim and Schafer, Discrete-Time Signal Processing ISBN 0-13-198842-5.
© 2016 Pearson Education, Inc.