USB sound card is used for oscilloscope and audio output at the same time: the tiny USB sound card cost less than 3 dollars, working environment is:
HW: Raspberry Pi 2 + HDMI LCD panel
SW: Xoscope (oscilloscope) and Rhythmbox (Musci and Radio) under Ubuntu Mate 15.04
First download Xoscope directly from Ubuntu software center, then from Control center, choose the USB sound card: CM108 Audio controller for sound input and output.
After finishing, open the Xoscope, choose sound card for input from its menu, then the USB sound card Mic input will become oscilloscope input terminal: to make a good probe will help measurement more better.
At the same time, open Rhythmbox to play music or radio, sound will comes out from the USB sound card headphone terminal.