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# Frequencies are inherently positive physical quantity.... what does it mean?

While I was going through a digital signal processing course, I came to this problem where it says that "Frequencies are inherently positive physical quantity" - Digital Signal Processing by John G Proakis, Page 15. I didn't really get the intuitive idea. Can anyone explain this sentence a little bit or suggest some resources?

Frequency is how many times something happens every second. So it can't be "minus 5 times a second". However when you do actual signal processing, you'll see negative frequency on the graph too.

Frequency is related to time. Time in systems is only positive. For theoretical purposes you can consider time to be negative, but in the real world time is always positive

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# Frequencies are inherently positive physical quantity.... what does it mean?

While I was going through a digital signal processing course, I came to this problem where it says that "Frequencies are inherently positive physical quantity" - Digital Signal Processing by John G Proakis, Page 15. I didn't really get the intuitive idea. Can anyone explain this sentence a little bit or suggest some resources?

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Frequency is how many times something happens every second. So it can't be "minus 5 times a second". However when you do actual signal processing, you'll see negative frequency on the graph too.

"Omg, my least important answer ever gets the most upvotes..." This is an inherent feature of how this website works. Short answers to simple questions can be verified (and upvoted) by many, while highly specialized questions only attract the attention of a few selected specialists. - Velvet Feb 5 at 12:44

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