Most of the games at the USC Games Expo event last week at the University of Southern California were simply on tables. But musical platformer One Hand Clapping sequestered itself in a quiet corner, inviting people behind a curtain, so they could have some privacy to explore its symphonic landscape. That’s because singing aloud is the only way to solve its puzzles. The PC game will be out for free later this year on Itch.io and Steam.

Players can use their voices to affect the game in a couple of different ways. In one puzzle, the pitch of your voice (how high or low it is) changes the height of the sand as you try to build a bridge to cross a canyon. In another, singing particular notes is the only way to unlock a path forward. As the game progresses, the musical challenges get more difficult. A later puzzle tasks folks to decipher a chord of notes, singing each one individually.

One Hand Clapping’s game director Thomas Wilson says that players’ comfort was their main priority. The team designed the game to be approachable by making sure the instructions are clear. People always know when they need to sing because of non-verbal cues. The musical puzzles also include recurring motifs and note progressions so that players begin picking up on the melody and getting better at it.

“We wanted people, over the course of playing the game, to feel more comfortable singing because it’s a very strange thing — to jump into a game and start singing,” said Wilson in an interview with GamesBeat. “People start off very nervous and uncomfortable. We represent that visually in the game by starting off in this harsh, hostile city where it’s very muted, both visually and sonically. And then, as they escape that and become more comfortable with their voice, by the end, they’ve dramatically improved.”

One Hand Clapping features striking colors — dunes of bright violet sand and deep orange mesas in the distance. The drawn environment has clean, minimalist lines, almost as though it’s trying to calm you and make you feel like it’s OK to do this strange thing: singing to a game. Wilson says they also tried to incorporate some humor as well, to make people more comfortable. And the team tried to compose a soundtrack that acts as “background vocals” for the player.

“We worked hard to make the music feel relaxing and not too overwhelming,” said Wilson. “We didn’t want to overshadow the player’s voice. Having it in the background makes the whole game feel musical. It makes you want to sing along, as opposed to just putting your voice out there, and that’s all you’re hearing.”

One Hand Clapping was one of the projects in this year’s Advanced Games Projects (AGP) course at USC. Wilson and his team had to pitch the game to the professors, and after they got in, they had two semesters to complete a playable demo. But even before AGP, Wilson had wanted to create a musical game.

Up through high school, he had always sang in choirs, but he stopped once he enrolled in college. He still had a love of music, though, and he said that a few summers ago, he began playing with the idea of making a game that “felt really visceral” and incorporated singing. He experimented at first with making a project where the colors changed depending on the notes the player sang. But he didn’t want people just to sing “arbitrary notes,” so he ditched that idea, and he and the One Hand Clapping team fleshed out a more melodic mechanic.

“I never joined any choirs in college,” said Wilson. “I guess I took it upon myself to use my major to get myself to sing. I’ve been singing every day for the past two years now.”