You’ll get something similar to what you see above, according to your sound hardware.
Controls are listed in the help page (press “k” for Keys), but most of it is done through the arrow keys.
Use the greater-than and less-than keys to switch between volume control and balance. Use the pipe to center the balance.
I like aumix for showing relative volume as you change balance, and for keeping balance separate from volume.
It also gives you a one-key channel focus (press “o” for Only), saved settings and an undo switch — things a lot of other mixers don’t do.
Any case, I’m glad to see this actually still works. I shall be more cautious in the future, I promise. 😳
P.S.: There is also a graphical version, if you are still tied to X. … Gasp. … 😯