Real world article
(written from a production point of view)
A Yridian symphony was a type of Yridian music mentioned in the script of DS9: "Starship Down".
The scene where it is mentioned takes place in a Jefferies tube on the USS Defiant. The Defiant entered the atmosphere of a gas giant planet and the atmospheric pressure was making the hull groan under the pressure. Jadzia Dax tries to take Muniz's mind off the danger by comparing the sound to a Yridian symphony. Dax adds her own counterpoint to it, making Muniz laugh. (Star Trek: Deep Space Nine Companion - A Series Guide and Script Library)