Sony STR-ZA3000ES User Manual page 187

2. Select a station on the FM band.
3. Press OPTIONS.
4. Select [FM Mode] from the options menu.
5. Select [Monaural].
Note
You can set FM mode in the options menu if the frequency indication is selected in step
3.
Hint
You can also set FM mode with [Tuner Setup] in the System Setup menu.