noun

• (music) A wide, flat board placed within, or forming part of the body of, a musical instrument in order to improve vibrations and increase volume.
  "To many a row of pipes the soundboard breathes."
• (audio engineering) A mixing console used to combine and blend different audio sources to a single output.
• (figurative) A sounding board.
  "Then, as now, they spent their days walking around the city they love, frequenting favorite restaurants or cooking meals at home, and serving as each other’s creative soundboard."
• (Internet) A control panel offering playback of various sound effects.
  "Check out these celebrity soundboards and play prank phone calls on your friends, family, and co workers..."