What is the difference between time domain and frequency domain?

Question

If a signal passes 1000 times in one second we say that its frequency is 1000. So one signal is moving in 1000th part of a second. It means, we can view a signal in terms of time. But I've heard that there are two domains, i.e. time and frequency. How they relate to each other and whats the difference between...

Answer 1

Speaking non-technically, a time-domain graph shows how a signal changes over time, whereas a frequency-domain graph shows how much of the signal lies within each given frequency band over a range of frequencies. A frequency-domain representation can also include information on the phase shift that must be applied to each sinusoid in order to be able to recombine the frequency components to recover the original time signal.

A given function or signal can be converted between the time and frequency domains with a pair of mathematical operators called a transform. An example is the Fourier transform, which decomposes a function into the sum of a (potentially infinite) number of sine wave frequency components. The 'spectrum' of frequency components is the frequency domain representation of the signal. The inverse Fourier transform converts the frequency domain function back to a time function.

Answer 2

They are (in one sense) reciprocals of each other. There are also relations between them which are described by things such as the Fourier (steady-state) and LaPlace (transient-state) transforms.

Doug