On the Focusrite 18i20 3rd Gen I find two problems with electric guitar going phono 1/4 jack into 1 and 2.
The first is that with the equipment monitor, two green bars is the most I can go because on the third bar it's clipping and then above that is total distortion.
The second is that my guitar always sounds thin and not full when recording. Also with microphones going into 3 4 5 6 (rear XLR) they all feel weak but when I go above two bars I risk clipping and distortion.
I should not need a DI box so my only conclusion is that I am not using things correctly. I have the software Focusrite Control. Any tips on setting everything up a bit better so that I can get things to sound louder fuller without clipping? What could I be doing wrong?
What you want in your DAW software is a good signal that produces a good waveform in your timeline. A weak signal is too small or flat. If your signal is too strong (going into the red on the unit) then it will clip because the waveform goes outside of the timeline's top and bottom borders. A middle ground signal isn't quite good enough for hearing the fullness of your tone either.
What you need to do are three things.
1) Go into your Focusrite software and it doesn't matter if you are using line or Inst setting that much as long as you have adjusted the gain on the hardware knob so that it isn't too low or too high. You should not hear clipping. You should try and get close to a good signal without clipping. This will give you a middle ground signal.
2) Now in the Focusrite software, in my case the 18i20 3rd Gen comes with Focusrite Control, find the channel that is receiving the signal. Notice you can adjust the level in this software? This is like a fine-gain control and you can push it more than the gain knob without clipping. So push it more until you think the volume has increased without clipping. Try to avoid yellow-lining and red-lining.
3) Record in your DAW software and notice how adjusting 1 and 2 influences the signal? With 1 your signal probably won't be hitting 0 but seems to be minus DB say, -6DB or -10DB. Don't push this volume up with your DAW software. You do it with the Focusrite Control levels. You can push it to the 0 setting. Line level.
Now you should have a signal that is everything you wanted. You can adjust it more in your DAW software now that it has been set to a nice line level.
In the next image you can see four hardware inputs in the top middle of the screen. Say it is the first one on the left that has your guitar. You can push this up more after you have set your gain level on the hardware without clipping.