Gain vs. Volume

In my experience, there is no clear understanding of the difference between the two out there. I've been getting advice that equated the two and then been told that it's all about matching the different components in the playback system without explaining what varying gain does to the sound .

To put this in context, both my phono preamp and line preamp have variable gain which allows experimentation with different settings. However, even before I bought my current phono pre, I noticed that there was a difference between a higher gain, lower volume setting vs. a lower gain, higher volume setting on my line pre. No matter how high the volume was, the sound was not the same with the lower gain setting. That told me that varying gain does something different to the sound curve than adjusting volume/attenuation does. The sound was more dynamic and "filling," as if the soundstage widened, and the sound was "thicker."

Now that both my phono pre and line pre allow gain adjustment, I have been experimenting with different settings. I'm still in the early stages of experimentation, the purpose of which is to find the setting at which the sound is satisfyingly rich and loud, but not too harsh, which I found a gain too high for the cartridge can result in, even if the noise level is very low.

So to sum up, it is very clear to me that gain and volume do different things to the sound even if the sound level is the same. I believe gain must be changing the sound curve so that certain frequencies are accentuated and ultimately affect the character of the sound.

If my hypothesis is obvious to anyone, please feel free to educate me, but so far I have seen no information on this forum or outside of it that draws a clear and sensible distinction between gain and volume.