Frequency Response of Linear Interpolation
Since linear interpolation can be expressed as a convolution of the
samples with a triangular pulse, we can derive the frequency
response of linear interpolation. Figure 4.7 indicates that
the triangular pulse 
serves as an anti-aliasing lowpass
filter for the subsequent downsampling by 
. Therefore, it should
ideally ``cut off'' all frequencies higher than 
.
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Triangular Pulse as Convolution of Two Rectangular Pulses
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Convolution Interpretation
