[PlanetCCRMA] Pentium-4 and denormal numbers on planetccrma

Steve Harris S.W.Harris@ecs.soton.ac.uk
Sat Jan 29 11:29:00 2005

On Fri, Jan 28, 2005 at 04:01:05 -0800, Fernando Pablo Lopez-Lezcano wrote:
> > Its a perfectly reasonable solution, sorry, I should have suggested it.
> > The thing to test would be to turn up the RT60 time as high as posible and
> > measure the amplitude of the output to see how much it affects the SNR.
> I just tried this: I connected hydrogen to jack-rack running the hacked
> freeverb (max wet output, no dry output, max room size, 0 damping, 0.5
> width) and jack-rack to bitscope. After stopping hydrogen the "smallest
> non-zero sample" shown on bitscope slowly falls down to a noisy -400db
> (the "largest sample" field hovers around -336db). Bitscope is handy :-)
> As much as I hate to introduce "noise" in the signal chain I think most
> probably -300db is quiet enough. I can't hear it, but maybe its just my
> aging ears :-)

I think a -300dB noise floor is quite reasonable, its well over the
FPU rounding error anyway :)
> The best thing to do, obviously, would be to figure out why the
> undenormal routines in freeverb are not doing their job. I look at it
> and it seems they are inserted in the right places. 

Its quite hard to catch them all, I prefer this soltuion and it means you
can remove the old denormal checks.
> Maybe this is the way to "cure" (as in "don't think too much")
> freqtweak, it also has denormal issues in its current release. 

I'm not sure it will work as well for freqtweak, as the situation there is
a bit more complicated, but its worth a try.

- Steve