The analysis of a system with respect to time is known as time domain analysis and with respect to frequency is frequency domain analysis. we usually change our systems from time to frequency by using (fourier, laplace ) to make it easy to understand the response of the system because time domain is more complex for higher orders.
I have a problem, I have a signal in time domain, actually, acceleration was calculated in time domain and the acceleration changes between [-4,4] m/s2. Then I did an FFT on the signal and converted to frequency domain; but the amplitude of acceleration in frequency domain is between [10e-4,1]. Why this difference? acceleration is normalized during the FFT transform or not?
What does FFT transform affect on the acceleration unit? is it m/s2 in frequency domain?
When a researcher uses the "second" or one of its multiples as a unit of measurement in her research or analysis, then it is in the time domain. e.g. An oscilloscope uses real-world signals in the time domain to visualize input. So we can say that, in Time Domain we analyze with respect to time. Other examples include time series data of economic indicators; or environmental data such as pollutants, heat, temperature, humidity; or sales of products etc.
On the other hand, when she is concerned with the reciprocal units such as Hertz in her research or analysis, then it is in the frequency domain i.e. we are analyzing something with respect to the frequency. The most common and familiar example of frequency content in signals is probably audio signals, and music in particular. Other examples are internet data transfer, television transmission etc.
Here is a picture explain time domain vs frequency domain signal.
Red graph is time domain and blue graph is frequency domain.
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