How do you turn sound off in IRC client colloquy?

How do you turn sound off in IRC client colloquy? I don't see any option to do so:

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Does this FAQ help? It looks like you can use Preferences → Alerts → Mute all notification sounds.

To access Preferences, use the keyboard shortcut Command + ,, or select from the Colloquy Menu bar item (just like any other macOS app).

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