Maybe it's not "a secret" but it's interesting, this:
> The gripping sounds, key to this videogame’s success, were an accident
“The speeding up of the space invaders was just a function of the way the machine worked,” he explained. “The hardware had a limitation—it could only move 24 objects efficiently. Once some of the invaders got shot, the hardware did not have as many objects to move, and the remaining invaders sped up. And the designer happened to put out a sound whenever the invaders moved, so when they sped up, so did the tone.”
[+] [-] TheRealGL|4 years ago|reply
[+] [-] giuliomagnifico|4 years ago|reply
> The gripping sounds, key to this videogame’s success, were an accident “The speeding up of the space invaders was just a function of the way the machine worked,” he explained. “The hardware had a limitation—it could only move 24 objects efficiently. Once some of the invaders got shot, the hardware did not have as many objects to move, and the remaining invaders sped up. And the designer happened to put out a sound whenever the invaders moved, so when they sped up, so did the tone.”