Possible Clues:

• Trumpeter's muffler
• Device for softening musical sound
• Flugelhorn accessory
• Change in nature, losing heart and having no voice
• Turn off, maybe
• Device that softens the tone of a wind insrument
• Cut off the sound
• Button you may click before a Zoom lecture
• "Sorry, I was on ___" (Zoom apology)
• Remote's "silence" button