《六韬·龙韬·五音》
太公说： 当敌人被惊动时就仔细倾听，听到击鼓的声音，那代表着角声；看见火光，那代表着徵声，听见各种兵器碰撞的声音，那代表着商声；听到敌人大声呼叫的声音，那代表着羽声；安安静静，什么声音也听不到，那代表着宫声。
太公曰： 敌人惊动则听之，闻鼓之音者，角也；见火光者，徵也；闻金铁矛戟之音者，商也；闻人啸呼之音者，羽也；寂寞无闻者，宫也。
Taigong said: When the enemy is startled, listen carefully; if the sound of a drum is heard, then that is the horn sound; if a fire is seen, then that is the zheng sound; if the sound of various weapons colliding is heard, then that is the gong sound; if the sound of the enemy loudly crying out is heard, then that is the yu sound; if there is nothing heard or seen, then that is the gong sound.