of Microprocessors

SOUND MODIFICATION METHODS 55
output and dividing it by the input amplitude, which usually remains const~nt.
The phase shift at a particular frequency may be determined by comparing
the two waveforms on the oscilloscope face. Note that phase shifts greater
than 180 0
leading or lagging cannot be uniquely determined at an arbitrary
frequency with this setup. However, a point of zero phase shift can usually be
found and the trend away from zero followed.
The amplitude response then is plotted simply by varying the input
frequency over the audible range and plotting the gain facror. Customarily,
the frequency axis is logarithmic in order to accurately represent a wide range
of frequencies, and the amplitude axis is scaled in decibels, which effectively
makes it a log scale also. The phase response may be plotted similarly,
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