I do not do much within RetroArch's settings, and my different monitors I use are just taken into consideration in the Pi's config file, where you can specify the resolution you'd like:
https://elinux.org/RPiconfig#Video_mode_optionsBy doing this, your Pi is delivering the proper video resolution to your monitor. This will ensure anything you do on the video settings in RetroArch will be correctly translated. I personally leave the settings. You may have well already done the config setting, as I've never had a monitor on my VGA666 work without having the correct resolution set.
As for the audio, the "white noise fix" is something I did on mine because I use the 3.5mm jack for audio.
https://github.com/RetroPie/RetroPie-Setup/wiki/Sound-IssuesThe volume I set on the mixer accessed from the Retropie Setup menu accessed through Emulation Station. I turn it up until it is red one notch then back it off one. About 88-90 out of 100 IIRC. Reason being, I see red and think to stop. I presume this may indicate clipping. Clipping is bad and can blow speakers a lot easier than too much power can. Plus clipping sounds like ---steaming pile of meadow muffin---. . The 3.5mm jack is fussy and am contemplating a cheap USB audio adapter as it is supposed to sound a bit better than the Pi's onboard audio. Helps when I run my CRT or PC monitor with an external amp in a cab, but on an LED TV at home the HDMI is the way to go IMO.
Aside from that, I am just starting to mess with RetroArch's settings and rotating games etc. The scaling is going to be important though I think, as I want to get as close to possible as intended with the reproduced image on the screen. Sometimes some trickery needs to be employed on certain games etc... I am not that far advanced.
I have 4:3 screens, didn't really try on the 16:9 TV though. For audio I only set the volume to 100 in Emulationstation. Works fine for me. The only thing I hate is that different games have different volumes.
Barry, I believe in RetroArch you can set the volumes for individual games, and then save the config, no?