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Do we have an article around here that explains waterfall? I've seen those graphs but I dont really know how to read them
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There is some information on waterfalls in the REW Help files, and I suppose the internet could google up a mess of great stuff.
Basically it adds the third dimension of time to your response graph.
The waterfall is derived from the impulse response by shifting the impulse response window to the right by a proportion of the time range to generate each succeeding slice. It has to be generated before you can observe it, so click the generate waterfall for each measure you want to see..
The slice slider shows you slices of time from the first response at zero time and then time is increased as you move to slice 30. So if you have the Time Range (ms) set to 300 ms and the resolution Window set to 300ms, each slice is 10msec after time zero. This shows what the microphone hears as time moves on from the initial sweep. If you have a resonance that tends to decay very slowly, you'll see it in the waterfall. This is what we're trying to reduce with the filters.
Create a waterfall of your measure and set the slider to zero. Then slowly move it out to 30. This is the decay of the signal in the room. It will tell you quite a bit where the room resonances are.
I don't have great pictures of this, but directly below is a waterfall of a perfect world system with no real resonance. See the signal decay to zero at about slice 13 (130ms) - beautiful. You see it's three dimensional. The regular horizontal and vertical is there, but now added is time in msec after the sweep.
Below that is a not so perfect system where you see that between about 20Hz-30Hz, there is room mode that is still ringing in the room way after the full 30 slices (300ms) have passed.. and you'll hear it too. Hopefully a filter will reduce this.
In the pic below that I show where you can overlay the before and after waterfalls and look at the results.................
Perfect world
perfect waterfall.jpg
Actual world with a bad resonance
real waterfall.jpg
Overlay the two
overlay.jpg
brucek