a young musician connects his electric guitar to a large black amplifier with multiple knobs and controls. He strums the guitar strings while adjusting the volume dial on the amplifier. The sound waves become visible as colorful ripples emanating from the amplifier's speaker, growing larger and more intense. The weak guitar signal transforms into powerful, booming sound that fills the entire room. Other customers in the store cover their ears and step back from the overwhelming volume. A store employee rushes over with a concerned expression on his face. an electronic device increasing the strength and volume of the guitar's sound signal