Related Clues:

• Sound in an empty room
• Come back
• Canyon sound
• 'Art is a delayed ___': Santayana
• Canyon comeback
• Reverberate
• Recording effect
• Iterate
• Baba for 20-Across
• It's been said before
• Gilda's Baba
• Muted effect
• Electric guitar attachment
• Bat's navigation aid
• It may bounce off walls