Thanks for answering, check that other users had the same problem, so check my settings thoroughly:
thanks to this help guide:
https://retropie.org.uk/docs/Sound-Issues/
This step solved the problem for me:
USING THE BUILT-IN HDMI AUDIO
If you have a standard RPi and want to send audio over the HDMI connector then it should just work. In some instances though, you will need to manually modify the raspberry pi boot config file (sudo nano/boot/config.txt) and ADD the following lines to those already there:
# forces HDMI mode
hdmi_drive=2
# Setting hdmi_force_hotplug to 1 pretends that the HDMI hotplug signal is asserted, so it appears that a HDMI display is attached. In other words, HDMI output mode will be used, even if no HDMI monitor is detected.
hdmi_force_hotplug=1
# Pretends all audio formats are supported by display, allowing passthrough of DTS/AC even when not reported as supported.
# May not be needed for all HDMI devices
hdmi_force_edid_audio=1
Once you've made the change, save the file, restart your Raspberry Pi, and move onto Step 2.