jaydev

I feel like I should know this meme, but don’t. I have 3 main questions:

1. Why does the multiplication of the 2 signals result in an extra fluctuation in the product?
2. Why would the low pass filter produce a flat line? Is it because it’s letting such low frequencies pass that none of the frequencies in the product signal are not included?
3. What does this have to do with locking in?