Make sure your deck's EQ is moslty flat as that can add tons of distortion. Keep bass Boost around 0 as that adds distortion. low pass and high pass all depends on what you listen to and what you are tuned to. Gain is touchy as it depends on what volts you are feeding the amp from the head Unit.....just dont max it out!!
so you mean, my Pioneer DEH .... sends 4v in output, should my amp gain be around that?
Also, why people say to play a song with level in FLAT, bass in minimum and everything in minimum?, say when it's already set, I would like to increase the bass, wouldn't that be different to as set up?
(while setting = flat, no bass in the headunit). after set up = say "POWERFUL", bass = say 3.
When you crank the HU it adds distortion when the music is louder. You can do it but if you have bass boost cranked on the amp it will butcher the signal.
I have mine flat untill I listen to like, Dragonforce or something with a lot of quick drumming. I then turn my Hu to low out of low/med/high. (premier as well)
Another reason for having the HU flat is that the amps should be set as they change the song. Changing the HU is altering the orignal signal from the song, so the signal has allready been altered before it hits the amp.