(Smoother) Cropping / Blending with Audacity

[Seeker47]

I'm pretty much a complete noob with this program, and would like to find a guide or advice on how to better blend joined sections (or different sound files) in a way that minimizes it sounding like separate pieces that were very crudely stitched together. Here is a very basic example, from a simple early attempt. I had this GONG.Wav file that just went on and on. Way too long for my intended purpose. But I still wanted the "starting from nothing" at the beginning and some of the "tapering off to vanishing" at the end. So I just extracted a longish piece from it and put the rest back together. I'll attach the result, which was borderline-acceptable to me but in no way feels seamless, as if originally made to this length.
Uh, looks like the forum has no provision for uploading non-image files. I'll do a RapidShare link or something, if anyone is willing to take a look at it.

[Bjs]

Select sections and apply required effect, either fadein or fadeout.
Split channel, and overlap lower channel parts with upper channel parts slightly
Save as mono, reopen new mono, and save as stereo, done

The only question that remains is the original time length, if its not an issue, ie, matching video, then there's no problem.

[Midzuki]

Avisynth's "Dissolve()":

{ http://avisynth.org.ru/docs/english/corefilters/dissolve.htm }

(just in case... you prefer the complicated way )