I would like to calculate some measure of volatility or noise for stationary time series data. This can be a measure for a single time series or a relative measure comparing multiple time series together. Let's assume a Dickey-Fuller test has already been conducted, and all the time series do not have a unit root.
What are some examples of such metrics to measure noise/volatility? I considered the simple "coefficient of variability" which is SD/mean. However, I am wondering if there are other ways to measure this. If it helps, I use R.
I know this is a vague request, and I apologize. I would really appreciate any suggestions or sources to learn about the topic.