Hi
I a trying to render the glass without noise but am unable to achieve it and ran out of sources... Can someone here give their expert advice on it or point out where I am wrong?


Thank you.

The setting's you have are pretty wild. But aside from that, your settings are the Karma CPU, and you are in Karma XPU mode.
So it is ignoring all of them, and defaulting to whatever sidefx has as a default.

But just looking at what is being rendered, you should enable the direct/indirect reflection and transmission AOVs to
be able to see the noise, and chase it down Vs blindly increasing multipliers hoping to solve it.
There seems to be some bad information out there regarding the adaptive sampling in Karma, the whole pixel oracle thing too.
I know your settings aren't being applied as I mentioned, but we should cover this anyway.

Primary Samples(pixel samples, AA samples, camera samples)are the total max per pixel ray counts to be fired.

The PrimarySamples section of the Advanced tab, by default it's using Variance oracle, and a threshold.
This is doing something quite cheeky, it's adaptive primary samples, Karma will fire a smaller amount of primary samples, far
less than the "Primary Samples" mentioned at the top, and if it sniffs out variance higher than the threshold, it will fire some
more out and repeat the process, but it won't ever go past the amount set in Primary Samples.
The default Minimum Samples is -1, telling Karma to "go for your life, you decide how little to throw," now you may take this
above -1, to 1-4 maaaaybe, to force Karma to do at least this many as a minimum. It's all a bit of a gamble, and it's designed to
carve off some un-needed sampling amounts of the Primary Samples.

Why is this good? Well for every Primary Sample, at least 1 secondary is going to be thrown, so if we can keep the amount of rays
flying around to the least possible we winning.

Your settings have them both at 2048, which is saying "use up to 2048, but also I'm going to make you use 2048" effectively killing any adaptive sampling in your render for Primary Rays.

Secondary Samples threshold can be useful to force Karma to not say it's bored and keep working, it's a bit dumb so you can be more explicit here, taking it to 0.005-0.001 would be sensible ranges if you are finding it being stubborn.

OCIO Transform, this should generally always be enabled, it's lifting the pixel values into what you will ultimately see, not keeping them in linear values, this can help raise up darker areas and make the sampling have a nicer time of things.

Indirect Sampling Quality
I enabled those AOVs, and it's pretty obvious that almost all your noise is coming from the transmission(refraction) in the indirect. So bumping the Refraction Quality up to 6 or so is going to multiply the Min/Max Secondary samples for transmission.
This solves pretty much all the noise, there's no need to increase the Diffuse or Reflection ones.
You could keep this multiplier lower, and up the Max Samples, but then it's possible you will over-sample everything.

Lights Quality, usually area lights aren't too bad, so I left the sample quality at 1 because they weren't showing up as being
major contributors to noise.

Below is Karma CPU



And Karma XPU - which I assume you meant to be using?
It's a far simple equation. We now have adaptive sampling, but nothing for indirect lobes.

so it pretty much comes down to enough Path Traced Samples, and setting the Variance threshold
to something that won't choke the render but also won't let things through too noisy.
Setting to 0.005-0.001 again is pretty much the limit.
And putting your OCIO transform on for the same reasons mentioned above.




Cheers,
L

WOW!!! such a detailed explanation and a corrected file. Thank you mate, This helped me so much and I learned a lot.

You're welcome Dude! It's a minefield out there, "rendering is a terrible thing" as a dear friend would say, so I'm happy
to try and help ease the tech burden if I can. Glad it helped.

L