TITLE: Speech processing pre-emphasis: how does it work?
QUESTION [11 upvotes]: In speech processing, the original signal usually has too much lower frequency energy, and processing the signal to emphasize higher frequency energy is necessary. To perform pre-emphasis, we choose some value α between .9 and 1. Then each value in the signal is re-evaluated using this formula: y[n] = x[n] - α*x[n-1]. This is apparently a first order high pass filter.
I am having trouble conceptualizing this, though. How does subtracting the previous value from all of the values eliminate the low frequency energy?

REPLY [3 votes]: This is just a derivative in discrete time domain. A high value means the signal changed rapidly, what means between the samples n and n - 1 there are high frequency components.