Digital engineers look at frequency stability in the time domain. This is because digital signals are, in most cases, viewed in this domain as pictures on an oscilloscope. Similarly, timing jitter, which is an interpretation of frequency stability, is also viewed on an oscilloscope as “blurred” signal edges.
RF engineers look at frequency stability in the frequency domain. They need much more precise measures of frequency stability, which are not available in the time domain.
Frequency stability can be interpreted in many ways by using a variety of measures. This is possible as the various measured quantities are all manifestations of the same noise in signal generation systems.
The generic term frequency stability is used because it is easily understood. However, it must be remembered that other interpretations may not necessarily be in terms of frequency.
Frequency domain interpretations are superior to their time domain equivalents. This is because they are complete descriptions. This fact will not be too surprising if you consider the measurement of distortion. A complete assessment of distortion cannot be made in the time domain. However, in the frequency domain, the magnitudes and phases of all harmonics can be measured, from which other parameters, such as total harmonic distortion ect., can be calculated. As will be seen, the same is true for frequency stability.