- Platinum Games composer Masami Ueda, from a Platinum blog post about the dynamic devolution of tracks in Nier: Automata.

Let's say you wanted to design a system that could take your game's soundtrack and play it in a significantly different way (say, as though it were composed for '80s hardware) on the fly -- how might you do it?

The folks over at Platinum Games recently posted a blog post breaking down how they did it for their recently-released Nier: Automata, and it makes for interesting reading if you have any interest in the design of dynamic audio systems for games. 

The post, attributed to Platinum Games composer Masami Ueda, explains that the Nier: Automata team wanted to play tinnier, more electronic versions of the game's music when the player accesses the hacking mini-game.

The team recorded original "8-bit" versions of some of the tracks on the game's soundtrack, but not all; those that didn't have "8-bit" versions were put through what Ueda calls a "Tone Filter" that smashed them down and mixed them back into the original track on the fly.

"First, we take the music we want to 8-bit-ize, and convert it from stereo into mono. Next, a 48-tone range (four octaves) is filtered out as a sine wave – drastically cutting out any very low, very high and subtle tones," writes Ueda. "Then distortion is applied to this range, changing its waveform into a square wave (a harsher sound associated with classic game consoles). Finally, anything difficult to hear after this is aggressively lowered and this processed tone range is mixed back in with the original track."

Even when the game does have a pre-recorded "8-bit" version of a corresponding track, Ueda says the game uses this tone filter to smoothly transition between the two pieces of music. You can read more of how it works in his full post, which also includes a diagram and several videos (one of which is highlighted above) showcasing the filter's effects.

On a related note, many of the game's developers make a cameo singing on the soundtrack, including game director Yoko Taro.