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Shown below is a video clip (QuickTime movie, with captions) of the closed lab.
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In this exercise, students generated two pure tones at frequencies of 2100 Hz and 480 Hz and mixed them into one audio file with a sampling rate of 44,100 Hz. They then downsampled the file at a sampling rate of 3100 Hz. The purpose of this exercise was to have the students observe that the 2100 Hz frequency component aliases as 1000 Hz because the sampling rate of 3100 Hz is not greater than twice the frequency of the 2100 Hz frequency component. The students had to apply the following formula to compute the frequency of the aliased wave: Given that f is the highest frequency component of an audio file, fs is the sampling rate, and ½fs < f < fs, then the frequency of the aliased wave will be fs – f.