Most 2048 implementations include a soft "thunk" when two tiles merge. It's a single synthesized note, around 220 Hz, lasting maybe 80 milliseconds. It changes pitch slightly as the merged tile gets larger — the 1024 merge is a half-step above the 512 merge, the 2048 is a full step above that. Most players don't consciously notice the pitch change. But they notice the absence.
I was playing a 2048 clone last week that had no merge sound. Just animation. The animation was fine — tiles slid and merged smoothly. But the game felt flat in a way I couldn't name at first. It took about ten minutes of play to realize: my brain was waiting for the thunk, and it wasn't coming, and the absence was registering as low-grade dissatisfaction that I was blaming on the game design.
This is the dirty secret of "game feel" research. The audio cues are doing more work than the visual feedback. The 130-millisecond slide animation tells you the tiles moved; the 80-millisecond audio burst tells you they mattered. Without the audio, the visual feedback is information. With it, the visual feedback is reward.
QuickFlipGame's 2048 implementation includes the merge sound. The rock-paper-scissors game includes a distinct chime for win, draw, and loss. The guess-the-number game has a soft tone for "too high", a softer tone for "too low", and confetti for correct. None of these sounds are loud or fancy. They all do the same job: convert mechanical state transitions into micro-rewards.
Game designers call this the "juice" — a slightly silly word for the collection of micro-interactions (sound, particles, screen-shake, easing curves) that turn a working game into a satisfying one. The interesting thing about juice is that it's almost entirely additive: removing any one element rarely breaks the game, but the cumulative effect of removing all of them is a 30% drop in player retention. Every individual sound is optional. The totality of the sounds is not.
The next time a casual game feels boring, try muting the audio and playing for five minutes. If the game suddenly feels like a spreadsheet, you've found the answer. The reason you play it isn't the game. It's the feedback loop.