"Sigma player" is an application that contains listening materials accompanying the teaching materials of the document. With "Sigma player", you do not need a CD player anymore for listening practice. Through this application, you can listen to the sounds of English sentences in places you like. You can also change the speed of the content. "Sigma player" makes listening learning easier and more convenient. Regarding audio playback of some English wordbooks, there are additional function settings that allow you to customize the order of playback individually.