Weird grainy noise when rendering

Hello,

i followed Andrew Price’s High Rise Building tutorial (http://www.blenderguru.com/high-rise-building/), but for a reason that eludes me i have strange artifacts while rendering.

Here is my test render after being about halfway through part2
http://dl.dropbox.com/u/7063219/render2.png

It’s most apparent at the lower part of the floors, and the balconies, this black dot-like noise. Also its a LOT more apparent if i turn on ambient occlusion, those areas are pretty much plain white with lots of black noise, no remains of the material color left.
As Andrew’s finished .blend renders without any problem, i figure it has to be something about the materials, or render settings, or whatnot, but i doublechecked about everything twice, without success.

So, if anyone cares to enlighten a noob, im thankful :slight_smile:

Raytraced AO ? How many samples ? approximate AO ?

tried AO off, raytraced, approximate, at 5 or 10 samples, the problem persists

for comparison:
same render with raytraced AO, 10 samples
http://dl.dropbox.com/u/7063219/render2_ao.png
its a bit more obvious there

That looks to me like a procedural texture with less-than-optimum settings for this scene. This is reinforced by the fact that it occurs in discrete places rather than across larger & more general areas of the rendering. Are you using the Noise texture in any materials? If so, try adjusting the parameters that control the size of the noise.

unfortunately its all base materials, most with default settings, some with less specular.
The only material that is not on default settings (apart from the background) is the glass, and its the same material in all places (railings on the roof, windows, balconies, railings around the base), but as can be seen only the glass in the balconies displays that behaviour

edit: also, the wall and flooring has the same material applied, and is the same object

The only other thing I can think of is coincident faces – two faces occupying exactly or nearly exactly the same location. This confuses the hell out of the render engine & often looks noisy. It’s also made worse by AO because the faces try to shadow each other.