First time with Corona and..

[maru]

Hello,

just a bit trick...

If you use a bounce light in the scene, thet's helps a lot to the render engine to calculating. That's not matter what light you have, HDRI or Sky and Sun or other. Where the Sun light hit to the floor, just drop there CoronaLight ( with correct celvin and intensity), and that will help a LOT for computing.  Useally there has a strong noise where the light is not lit the scene correctly. Good solution to lighting thet area with low light setup.  ( Depend of the scene of course ). And if necessary after correcting the camera setup. The result is more clearer light passes.
If I have a problem with light noise, I always use this metode and I'm useing the 32/4 sampling balance. Ofcourse this is depend of how noisy the light passes and I have a correct albedo too.

Don't beleve it, just try it if you want.

Noise is usually caused by randomly sampling bright and dark areas. This way you add more light to your scene and provide better direct sampling. But your scene won't be physically correct any more.

[Fibonacci]

Yes, your right Maru ! But when I have just a small window without enought light intensity ( I beleive the stronger HDRI multiplier is not the correct way to make more light in the scene) and lot of noise in the direct and indirect light (with pumped up samplings ), some softbox or bounce light helps a lot to lit the scene and in the result you can't really see it. Only dim light and helps to cleaning up the noise. Maybe not the physically best way, but like in the real photography help to lit and here help for the renderer. For the interiors - I beleive - it's not really matter.

Maybe I'm wrong...but ofcourse I have to check this new info. New for me.
https://coronarenderer.freshdesk.com/support/solutions/articles/5000518064

but, at this point that trick helped me a lot.