Figure 1a—This is a waveform of the voiced sound "ee" as in "speech." The arrow points to high-frequency wiggles corresponding to the second formant (F2). Note that these wiggles do not cross the zero axis. b—After preemphasis or high-pass filtering, the F2 components now cross the zero axis with the same waveform. c—After being infinitely clipped, the waveform of Figure 1b is a square wave showing both F1 and F2 components. This signal is applied to the microprocessor via a digital input pin.

a)  

b)   

c)