The beats are actually two new sounds.
Their frequencies are (the sum of the original two frequencies) and (the difference of the original two frequencies).
The existence of the beats is the result of the difference in the frequencies of the original two sounds. <em> (b)</em>
1 and A
2 and B
3 and D
4 and C
An analog signal carries information by copying an original sound
When we speak through the microphone, it turns our sound into some sort of electronic wave.
This electronic wave is caught by a recording device and later could be replicated into Mp3 file that we usually listen to