putting error bars/standard deviation in my graphs

Hi.

I have a data of 600 timesteps from 6 different channels in a matrix X. This means the size of X is 600 by 6. I plan to plot the average of X over the number channels, so that the mean of X will just be 600 by 1. I want to include standard deviation bars/error bars, but only for every 50 steps (starting from t = 50, t = 100, and so on).

I am confused how to implement this. Your help will be appreciated.