afternoon Doof...
1st, a decision needs to be made regarding priority.
What's more important - the 100 track list length or the "no more than 3 songs by any artist" rule?
You can't have both as each instruction requires a list modifier, so, if you limit to 100 tracks, then limit the tracks per artist, you could end up with less than 100 tracks, and the genre ratio would change too. If you limit to 3 tracks per artist first, then limit to 100 tracks, you'll get 100 tracks with the correct genre ratio, but the only guarantee you have is that no artist will feature more than 3 times in the list. As the latter sounds/feels more desirable, I've outlined the steps below:
1. set the [media type] to audio
2. use the "Limit (advanced)" modifier to limit the list to no more than 3 tracks per artist.
3. use the "mix" modifier to return the desired number of tracks with the desired ratio of genre
Unfortunately, as we're still on Smartlist Wizard v1.0, we're expected to know the required syntax to work with both modifiers mentioned above. The wizard cannot build the required strings for us.
The final string would look like so:
[Media Type]="audio" ~limit=-1,3,[artist] ~mix=100,50%,{g=rock},25%,{g=ballad},20%,{g=electronic},5%,{g=folk}"g=rock" will draw from all genres that contain rock, ie. rock, rock/pop, heavy rock etc. etc.. To get rock and only rock, you would use g=[rock].
Pointers on using the modifiers can be found
here for "limit (advanced)" and
here for "Mix".
Obviously, far from ideal for new users who could not be expected to know these things. The help button opens the help file in the appropriate area, after which the user needs to click the link to search rules and modifiers, then find and understand what they are looking for. It doesn't help that in the table, "Limit (advanced)" is referred to as simply "~limit".
I don't think this was quite the answer you were hoping for, but it's all we have at the moment.
-marko.