Howtosignalprocessing
- What is the physical meaning of negative frequency?
- What is the meaning of negative frequency in Fourier transform?
- Why we have negative frequencies needed in the spectrum?
What is the physical meaning of negative frequency?
Negative frequency is an idea associated with complex exponentials. A single sine wave can be broken down into two complex exponentials ('spinning numbers'), one with a positive exponent and one with a negative exponent. That one with the negative exponent is where you get the concept of a negative frequency.
What is the meaning of negative frequency in Fourier transform?
Also, Noteworthy is the point that a negative frequency is the rotation vector in the opposite direction to the positive frequency. For example it is necessary to have a real (non-complex) signal. Then we have two vectors rotating in opposite directions.
Why we have negative frequencies needed in the spectrum?
Negative frequencies are just a mathematical construct to allow us to analyse real signals using a complex number framework, which is used when looking at double-sided spectra. A complex number can only be made real if you add to it its conjugate, e.g. (a+bj) + (a-bj) = 2a.
