Fuser developers explain how the music game’s mash-up magic trick works

Playing Fuser feels a bit like witnessing a magic trick. Developed by Harmonix, the DJ game is essentially a mash-up simulator that allows players to pull tracks from different songs and seamlessly slam them together. Combine the bass from Weezer’s Buddy Holly, the drums from Smash Mouth’s All Star, and the vocals from Lil Nas X’s Old Town Road in any key and tempo, and it’ll somehow create a coherent piece of music. It feels like it shouldn’t be possible — but it is.

Fuser was quietly released in November, on the same day that the Xbox Series X and S launched. The music game got a little lost in the next-gen mix as a result, but a new free demo is available now and it’s giving new players a front row seat to the magic show.

Ahead of the demo’s launch, Digital Trends sat down with the Fuser team to discuss how the game pulls its impressive musical feat off. According to the game’s creators, the secret to its success is the same thing that can make or break a party: A carefully planned soundtrack.

The Lizzo effect

As Fuser Project Manager and Guitar Hero veteran Daniel Sussman succinctly puts it, “Guitar Hero is a game about rock music. Fuser is a game about DJ culture.” That means that Harmonix had a tricky task ahead of it when it came to replicating the world of unlikely mash-ups.

To players, it may seem like the studio has developed a system that allows for just about any song to be tossed into a mix. From a developer side, that’s not quite the case. Fuser features a heavily curated playlist of songs that need to follow a handful of rules to work with the game’s system. For one, every song needs to be in a 4/4 time signature. That means the game can’t feature waltzes or something as complicated as Radiohead’s 15 Step. Fortunately, most popular songs utilize 4/4, so there’s no shortage of songs to choose from.

On top of that, certain instruments or types of sound don’t tend to mesh with the game. Sussman says that “heavy guitars” are among the textures that tend to stick out most. He affectionately refers to that kind of texture discordance as “The Lizzo Effect,” based off of early experiences of watching fans try the game.

“We went back and forth about Lizzo’s Good As Hell because the horns have a certain quality to them that can sound off in some songs,” Sussman explained. “Whenever we demoed the game at a convention like PAX and we’d see a player suddenly make a weird face, we’d say ‘Yep, they just dropped the Lizzo horns.'”

Sussman notes that not every song the team wants in the game necessarily works due to these factors. Still, Fuser is able to pull from a wide range of tracks thanks to its unifying time rules that bridge the gap between disparate genres as well as a proper DJ can.

Not my tempo

While time signature and texture play a key role in making sure songs fundamentally work in the game, tempo presents its own set of challenges. The further a song’s initial tempo is pushed and pulled, the more it starts to distort or sound out of place. That’s why Fuser only plays songs between 90 and 157 beats per minute, presenting a sort of safe midrange for tracks to bounce between.

Fuser

While Harmonix has to pick songs that work in that range, the studio has some clever workarounds for tracks that are way higher or lower. Fuser audio lead Eric Brosius explains that the game utilizes double time and half time to open up the possibilities.

“Let’s say we do a punk rock song that’s around 220,” Brosius explains. “What we tend to do is think of it as 110 in the game. And therefore, when we’re stretching it from 110 to 90, we’re not stretching it all the way down from 220. So it’ll sound like 220, but the game is considering it at 110.”

Harmonix will make small adjustments to songs as well to account for things like tempo breaks. That explains why Billie Eilish’s iconic, but metronome disrupting “duh” in Bad Guy doesn’t appear in the game’s mix. While Brosius says the studio tries to present songs as faithfully as possible, the team rearranges songs here and there to make sure all of its more iconic moments happen in the span of 32 bars.

It’s all in the details

While those high-level rules are immediately apparent, Fuser has tons of additional details that help the experiment. For example, the game uses its own real-time mastering chain that each disc runs through, which compresses individual songs. Harmonix will even subtly tweak the brightness of songs to make sure they don’t get smothered in an eclectic mix of genres.

“Sometimes old-school hip-hop songs are heavy and bassy. They have that record player quality to them,” says Brosius. “Anything that’s an electronic music song is very bright. That’s just how we mix music these days. So we adjust that.”

Fuser

Even the game’s freeform instruments, which allow players to create their own loops, follow a specific set of rules. Plink around on a piano in Animal Crossing: New Horizons while a K.K. Slider song plays and you’ll vaguely meander around in the right key. Fuser goes one step further by actually locking players into a chord progression behind the scenes.

“We determine which disc should be the chord progression master and we pipe that information into the instruments so they follow the chord progression,” says Brosius. “I believe we weigh the bass the strongest. The bass has a lot of the harmonic information, so we think of it as where a lot of the chords are played.”

Like Fuser’s eclectic mixes, every little rule and trick blends together to form a seamless mash-up system. The most successful thing about Fuser is that players don’t have to think about any of this while playing. It’s as simple as clicking a button and making some noise.

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