Trojans are malicious applications that pose themselves as legitimate software in order to trick users to install them. Once on the victim's machine, it may run any number of malicious process to steal vital information or inflict damage to other software.
This is a trojan that originates from China. Troj.Soundmix drops several .dll files to the infected PC's system32 directory without an internet connection. These .dll files are disguised as important sound card resources.