# Translations:Magnitude spectrum and phase spectrum/1/en

What are the amplitude and phase characteristics of a digital filter? The filters we discussed in Chapter 5 operate in the time domain. Therefore, they can be called *time-domain digital filters*. The numerical examples presented there illustrate digital filtering in the time domain. However, many people are more accustomed to thinking about filtering in the frequency domain. One can study the action of filters profitably either in the time domain or the frequency domain or in a combination of both. The choice of a particular approach depends on the nature of the problem at hand. We shall now proceed to sketch the relation that exists between time-domain and frequency-domain filtering. Before doing so, a brief discussion of simple harmonic motion is in order.