This is hardly magic but it’s something that I’ve figured out which may help new Renoise users. Sometimes if you have a pattern with automation on it and render it to a sample, there will be a weird pop at the beginning. This is because Renoise is “moving” the device’s setting from where it is before you render to where it is at the start of the pattern. An example would be a filter, where at the beginning of the pattern the cutoff is at 0 and halfway through the cutoff is open. If you stop playing mid-pattern and render the selection to a sample, the start of the sample will have a weird pop because of how Renoise processes the automation points.
The solution is simple: enable “follow player’s position” and move your cursor to the first line of the pattern before rendering. By doing that, the devices are set at their starting points before rendering, which avoids any movement at the beginning thus avoiding a weird pop.