Guardic is the little-known predecessor to Guardic Gaiden on the Famicom, better known as The Guardian Legend on the NES.
Wait at the title screen until the High Scores screen shows up, then press Left, Right, Left, Right, Left, Right on the keypad. Use the arrow keys to navigate the sound test, and press Space to play the selected sound. Switching to another track will immediately stop the music.
To go back to the title screen, press Esc.
Area Select (Practice Mode)
Press Left, Right, Left, Right, Left, Right on the title screen.
Once in Practice Mode, press Left to select the next area, and Right to select the previous area. Press Space to enter the selected area, and Esc to leave Practice Mode at any time.