The normal commercial disc is engraved with two sound-bearing concentric spiral grooves, one on each side, running from the outside edge towards the center. The last part of the spiral meets an earlier part to form a circle. The sound is encoded by fine variations in the edges of the groove that cause a stylus (needle) placed in it to vibrate at acoustic frequencies when the disc is rotated at the <answer>correct speed</answer>. Generally, the outer and inner parts of the groove bear no intended sound (an exception is Split Enz's Mental Notes).
Does it matter at which speed a disc is spun?
correct speed