Amazing Tip about I was reading, Thought I share :)

Creating complementary EQ curves

We now know that it’s best to make EQ decisions in context, based on how we want to push and pull the listener’s focus and compliment all the instruments and song as a whole. We also know that frequency and pitch are directly related. And therefore, elements playing in the same octave are in danger of competing with each other and may need special consideration in regards to EQ to sound good in context. Simply boosting an instrument’s fundamental frequency tends to make instruments blur together in the mix...... 
http://corner1stop.com/open-sounding-mixes/

Nice tip. Thanks for sharing!

Another interesting trick is that the brain detects the fundamental based on the spacing of the harmonics (missing fundamental phenomenon). A common use for this is kick/bass collisions, since the kick is typically discreet, and the bass covers a couple octaves in most cases. Only a couple dB is sufficient; but when discreet harmonics exist, the fundamental itself can be lowered fairly aggressively.

Fender's original bass amps, the open-backed Bassman combos nowadays loved by many guitarists but not many bass players, couldn't put out the fundamentals of the bottom octave of a bass at much volume at all.

Nor can most common "hi-fi" speakers, which typically start to roll-off at around 100 or even 200Hz

They do however put out the harmonics, with the result our brains fill in the missing fundamental pitches like they do when hearing just the third and fifth of a major or minor triad, a trick used by jazz guitarists quite a lot.

Strange and complicated things, psychoacoustics.

You guys are very welcome.

I've never understood when people talk about boosting the fundamental of an instrument. Surely that fundamental changes with every different note. I might play within a range of two or three octaves on guitar. That's a three octave range of fundamentals.

Yes they would change due to pitch,= frequency, but also still lives in around 150hz - 1k 

But as far as how I would mix it in a track is, I would look or the main fundamentals of the source and use that to mix and keep that in spot, and let the performance jump in octaves beautifully, but still having the root fundamental. But If you play constant octaves in each verse, bridge, chorus etc.. for example , I would approach differently in adjusting each part..   Hope that  helps .