if i had some track sounding loud, wich level is correct to turn down, the track level or the plugin level in the track? (ex: slate digital trimmer, scheps omni channel, etc)

 

if it was in my daw, I would negative gain the region so I could leave everything where it is. unless you have some extreme setting on the plugin, I would decrease the signal into/out of the channel first.

 

imho better at the plugin level. that way your channel fader is at the normal position, when you go to mix your track. but please at the output of the plugin, otherwise any distortion, compression etc will be affected.

 

If that level has increased after adding a new plugin, you should first decrease the output level of the plugin so as to properly match the volume levels and make a correct comparison. After that, you may use use your track fader to bring it to the level required.

 

Learn proper gain-staging. Therein lies all the answers.

That said, sometimes you want to drive the analog emulation plugins but still keep healthy gain-staging (by turning down the plugin output volume). Is that your question?

 

If you're talking about a possible (sound) difference between lowering a plugin's output and lowering the fader, there is none.
Try yourself, duplicate a track, lower the plugin in one and the fader in the other (by the same amount, ofc), phase invert one of them -> gone. No difference at all.

 

yesssssssssss

 

Then the answer is "proper gain-staging". Deliberate overdriving and compensation.