Force 16:9 on a 4:3 monitor/tv

[FlyingTomahawk]

Is there a way to force/keep a 16:9 aspect ratio on a 4:3 monitor/TV?
I found an old 4:3 monitor but the theme and all my setups are made for a 16:9 setup. I wouldn't mind to have bars on top and bottom as long the aspect ratio stays 16:9. So is there any setting I can enable on the RPi 3 to force everything, ES and emulators, to show in 16:9 aspect ratio?

Pi Model or other hardware: RPi 3
Power Supply used: 5V 4A
RetroPie Version Used (eg 3.6, 3.8.1, 4.1 - do not write latest): where to check this
Built From: Pre made SD Image on RetroPie website
USB Devices connected: wireless RF receiver from a xbox 360
Controller used: self made xbox360 wirejess arcade stick
Error messages received: none
Log found in /dev/shm/runcommand.log (if relevant): -
Guide used: none yet
File: no file issues, I think
Emulator: lr-fbalpha
Attachment of config files: -
How to replicate the problem: connect to 4:3 TV/monitor

[herb_fargus]

@flyingtomahawk I'm not sure the exact numbers but I believe this is the config you'll want to mess with:

www.raspberrypi.org/documentation/configuration/config-txt/video.md

[FlyingTomahawk]

@herb_fargus

Thanks Herb.
I'll give this a try and report back asap.

[FlyingTomahawk]

I tried all kinds of hdmi_group and hdmi_mode combinations but nothing seems to work as I was expecting. I use an HDMI to DVI-D adapter to connect the RPi to the monitor.

Guess I'll either have to use a 4:3 compatible theme or get me a 16:9 monitor in the near future.

[Ecks]

Have you tried the overscan setting?