The Journal of Gambling Studies published a study concluding that players prefer slot machines with a lot of sound effects because they’re more rewarding.

The average number of sound effects in slot machines is 400. It includes the sounds that play when the game is loading, when it’s idle, background audio during different parts of the game, and celebratory sounds.

The study focused on the sounds that follow winning combinations. Often it resembles coins falling. The sound appears even when the amount won is smaller than the amount wagered. It disguises a loss as a win.

The 96 participants in the study played two sessions, with and without sound affects after wins, whether disguised as losses or not. Their level of physical excitement, for example palm sweating, was monitored. After the sessions they chose the one they preferred.

Both criteria showed that the session with sound effects was much more exciting and enjoyable. The players also overestimated up to 24% how many wins they had when sound effects were on, compared to 15% when they were off. That’s the reason why online casinos constantly improve the audio in their offer.