Hi, I'm trying to get a reasonably accurate distortion measurement for a project I'm designing in LTspice but I've not had any practical experience with FFT analysis and I don't know if there are any tips/tricks to getting accurate results.

I turned off compression options.
I let the circuit stabilize for 1 second before recording data.
I set the maximum time step to 1us.
This is what I got

The lack of distortion is pretty good considering almost no NFB is used but that slant makes me sad.
This is the simulated readout for an amplifier that I currently own.

Also kind of slanted.
Is that slant normal in practical designs?
Is the first readout good/bad?

 

You might want to post your .asc file.
Off the top of my head I think at 1Khz you should measure 0 Db.

 

I'd love to post the file for the top one but it is my pet project and I don't really want to put it up on the internet, at least not right now.
Plus it's so complex it's an eyesore to look at and takes my overclocked 4770k hours to even begin loading the simulation. Had to wait half a day for the results.

As for the second one I attached on the bottom. It leaves a lot to be desired but it was bought before I got into DIY, however it does sound insanely good with the right adjustments and modifications.

Edit: I updated the first pic to a more accurate sim compared with the other amp.