That's an excellent noise reduction. How did you do it?
Well... I did not
Perhaps I should have been clearer as to what I was showing in that example. I was responding to Roman's suggestion:
... you can get away with just 1 exposure and just double process that image...
By that he meant that you would take a singe RAW exposure and underexpose it in post by one or two f/stops (to preserve highlights) and send it to Photoshop as a separate file, and than you would take the same single, original exposure and overexpose it in post by one or two f/stops (to open up shadows) and send it to Photoshop as a separate file. In Photoshop you would then blend the two files manually, taking the best parts of both (ie, highlights from one and shadows from the other).
My response to Roman's suggestion was that it is certainly possible to do it that way. However, by overexposing the file, to lighten up the shadows (ie, underexposed areas), you are risking increased noise in those areas.
To demonstrate that, I took two files from my series of three bracketed exposures (reply #19). The one on the right, the noiseless one, is simply a 100% crop of the overexposed, third shot in the bracketed series (ie, where the shadows were properly exposed). The one on the left, the noisy one, comes from the first shot in the bracketed series (the darkest one), which was then overexposed in post to open up the shadows to the same level as in the image on the right.
The bottom line: if you want to avoid/reduce the noise in shadows, give it plenty of light, either by ETTR in a single exposure, or by bracketing.
