Elenco Upgrade Kit SC500 to SC750 - Manual (Page 109)

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The waveform shown here is from humming into the microphone,
notice how the tops of the pulses show a regular pattern of dips
now.
Look ahead to the Microphone project PC14 on page ??, and note
the waveform shown there for humming into the microphone:
Notice that you can see roughly the same pattern in the peaks of
the waveform at left. If you hum at a similar tone and at a similar
distance from the microphone, you will get similar results.
If you talk into the microphone now you will get different patterns
depending on what words you say, how loudly you say them, and
your distance from the microphone.
Words produce a more
“random” pattern than humming, but less random than blowing into
the microphone. The waveform at left is an example of talking into
the microphone. Observe the waveforms you get and compare with
what you get in project PC14.
And so you see that your voice is being superimposed onto the
peaks of the stream of pulses, this is called Amplitude Modulation
or AM. At AM radio stations music or voice is superimposed on a
high frequency waveform (similar to the pulse stream here), filtered,
amplified, and transmitted.
Doing this allows the music to be
transmitted over great distances.
You can place Winscope into FFT mode to view the frequency
spectrum if you like, but it will be confusing to look at.