[plug] Micorphone problem on Pi 4

[M S R Wood]

I have a headset attached to a USB sound card dongle. When this is
connected to my Pi 3B it works perfectly. However on my Pi 4 the
microphone does not work. It is detected  by an assortment of websites
but sound is not passed through.

The Pi 3B uses the default Pi operating system.
The Pi 4 uses the Lite version to which I have added Xfce and various
applications. I'm wondering if I need to install some specific
software to make the microphone work properly.

Any suggestions?

Margaret