Grading format:
Homework 4 was mainly graded for completion and theoretical understanding of the problems.

TA Comments:
Students generally did well on this homework. The most difficult problem is Question 1 on interpolation.
- Zero-order hold (also known as zeroth-order interpolation) involves convolution with a causal rect in time. In frequency, this is multiplication of the spectrum of the signal with the spectrum of the rect (which is a sinc). This is effectively a coarse low pass filter to remove high frequency aliased replicas.
- First-order interpolation involves convolution with a mixed-causal (symmetrical about t=0) triangle. The key is to realize that a triangle is the convolution of two rect's - producing a $ sinc^2 $ in frequency. This can also be thought of as a coarse low pass filter but with a sharper cutoff than zero-order hold.

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