I had a conversation with someone that took place outdoors. We recorded a 30 minute conversation on an Olympus digital recorder. The Olympus digital recorder did an outstanding job of recording the entire conversation except for one important part of the conversation that amounts to about 10 seconds of totally unlistenable data. Those important 10 seconds of the conversation are not the least bit audible due to major background noise. The background noise is mechanical. The background noise was made by a garbage truck making its rounds, it was in the process of lifting a dumpster up from the ground, up into the air and then crashing the dumpster back down to the ground again. Is it possible to TOTALLY eliminate the noise of the garbage truck in the background thereby making those 10 seconds of unlistenable data 100% audible to the listener? On a scale of 1 to 10 with 10 being 100% successful in accomplishing this; and 1 representing almost zero chance of accomplishing this, what would you rate our chance of restoring those 10 seconds of lost conversation, a one, a ten or something inbetween????
My personal opinion is you have about a 1 in 10 chance of removing excess background noise from a recording like that.
Well, i remember this Demonstration on a CD back in 1996 or 1997, where they used the Waveeditor "Sonic Foundrys Soundforge 4" (or a plugin for that Software) to remove background noise (which can be a not that agressive vacuum cleaner or something like that). And it really did a great job removing the vacuum cleaners noise.
But i doubt, that this noise remover, which was not really a noise gate, but a more intelligent processing algorithm, will remove such a harsh noise completely.
Today, Soundforge can be found here: http://www.sonycreativesoftware.com/audiostudio , but i don't know if this special "Noise Remover" is still a part of that software or an available Plugin for it. :?
You may try the Demoversion of Soundforge, if you like. Maybe they integrated the "Noise Removing Algorithm" to the mentioned Waveeditor (Soundforge) .
When trying to process 'noise' out of my ambiance recordings to capture the wing flutter of some crested pigeons, I ran a spectrum analyser over the parts with the wing sounds and again on the parts without the wing sounds. I then isolated the frequencies of the wing flutter and using EQ, removed the rest of frequencies. It worked reasonably well - not perfect but I was able to isolate the sound. In your case you could try the reverse, find the spectrum peaks for the truck and dumpster and with EQ, remove them and see if the dialogue pops out. Its NOT going to work 100% but may succeed in making the dialogue 'listenable'.
Or try the demo version of IZotope RX