Hi, on behalf of a friend who is a great musician but not so hot on the innards of computers. He has installed jammr on his macbook (Pro?) but the speakers do not mute when he plugs in headphones. We suspect that his internal microphone is also disabled as I only hear hum from him on my windows laptop. There are apparently sound settings preference windows in Mac OS. The Mac one has a headphone output option but the similar window in jammr preferences does not. If you can advise where to start I'll hand over to him.

Hi JazzDave,
Please make sure that sound devices are connected to the computer before launching jammr.

After jammr has started and your friend has logged in, go to jammr | Preferences to check the input and output device.

The output device name may not say “Headphones”. It could be “Built-in Output” or similar if your friend is using the computer's built-in soundcard.

There is an audio setup guide here that may help:
https://forum.jammr.net/topic/1987/

If you would like me to review the audio configuration, please go to Help | Show log and copy-paste the technical information that is displayed on this forum.