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I am trying to get my volume to render smoother without using denoising in Cycles. Testing various render settings for volume I can't seem to achieve the desired result. I figured the volumes step rate render setting would do this, since that is how it's described, but after testing I wasn't able to discern any noticeable difference between values of 0.1, 1.5(default) and 5 even when zoomed in 500%. Sample rate of 2k to 5k doesn't show much improvement. I'm wondering if it's not a setting in my principled volume shader, or maybe my lighting setup (hdr + 5 points, 3 areas) though the main light running through the volume is the hdr.

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  • $\begingroup$ Hello :). Out of curiosity - why not use a denoiser? Cycles isn't very good at rendering volumetrics, and even with 10K+ samples denoising really helps to smooth the details. $\endgroup$ – Jachym Michal Apr 1 at 12:41
  • $\begingroup$ Optix denoiser tends to give the best results, but even then it seems to make things look almost cartoony, smoothing out fine details, etc. I suppose I could do two renders, one with optix denoise and one without and then blend the volume areas in photoshpo... But, if there was a way to smooth the volume i would just do that. $\endgroup$ – Rob Proctor Apr 1 at 13:00
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There are two settings that affect this - one is the 'Step Rate' that you have found, the other is the Max Steps - and both have an impact.

It used to be that the two settings behaved individually - and the volume would be rendered with a 'Step Size' and then if the Max Steps was reached the volume would simply be ignored for the rest of that light ray. This was fine in most cases but could produce unexpected results, with the volume effectively "cut off" as soon as the limit was reached. Furthermore, changing the Step Size while leaving the Max Steps unchanged would change how much of the volume was rendered.

Now the Step Size has been replaced with the Step Rate and the Max Steps has been enhanced so as not to cut off the render by automatically generating a 'Step Size' behind the scenes based on both the Max Steps and the Step Rate. This means that reducing the Max Steps will no longer cutoff the volume but will affect the size of the steps - so having Max Steps set too low will limit the effect of more precise Step Rate.

The solution is to increase Max Steps to allow the Step Rate to have more of an effect. This will increase render times since more steps are required to traverse the volume but can produce more detail in your volumetrics.

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  • $\begingroup$ I appreciate your detailed response, however I didn't mention in my original post but I had also tried playing the max steps, from the default of 1024, to 2 and to 4096, none of the values made any difference, at all, to the render. Again, zoomed even to 500% I couldn't discern any change in the pixels. $\endgroup$ – Rob Proctor Apr 1 at 14:17
  • $\begingroup$ On another note, I noticed that under light bounces volume was set to 0, increasing it to 4 helped slightly, but even at 12 the volume is still a bit too grainy. Im on 2.9.3 alpha, I wonder if that may be related.... Or now that I think about it, maybe I needed to increase the light bounces first and now the volume step values will make a change? I'll have to retest and see. $\endgroup$ – Rob Proctor Apr 1 at 14:19
  • $\begingroup$ It would probably help to be able to see what you're referring to and to be able to replicate your setup. Please could you update your question with images showing your results and nodes and geometry setup and highlight exactly which bits you have issue with. $\endgroup$ – Rich Sedman Apr 1 at 14:21

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