Vertex Dispenser

Dynamic Music System Design - Video Game

  • created by: Michael Brough

The Game

Vertex Dispenser is an abstract, real-time strategy game with some geometry and graph theory baked in. Creator Michael Brough had made the entire initial version of the game himself, including abstract, generative backing music where various synthesized notes and samples were triggered in time with player actions and other game events. After I play-tested a version of the game, Brough and I discussed wanting to add more rhythmic structure to the music to better support the gameplay’s action-oriented elements. This is where I came in.

Dynamic Music System


It was crucial that the added music be very agile in closely tracking the dramatic shifts in the game - in particular, the differences in feel of base-building vs. fighting other players, which in Vertex Dispenser could be shifting back and forth within seconds. A typical approach of crossfading drum loops could provide variety, but wouldn’t be able to react quickly or deliberately enough without sounding forced and unnatural.

To solve this problem, I developed semi-generative dynamic music system (which Brough coded into the game) and created the synthesized drum and bass sounds that it uses. The drums consist of 129 short phrases divided into three groups: building, more active fighting, and less active fighting. Below are a few examples of isolated drum phrases:

Within each of these groups, the phrases are sorted by increasing intensity. To play the drum track, the music system picks from these phrases in a semi-random fashion, one after another to chain together. Short-term game-state determines which group is picked from, while a longer term, behind-the-scenes intensity level (based on many different game inputs over time) dictates what part of the range within the group is most likely to be chosen from.

The phrases are short (around 2 seconds between each phrase being played) and designed to naturally overlap. Therefore, the system creates a natural-sounding, non-repeating drum track that is able to react to the game on multiple levels and switch modes very quickly - all while still sounding musically structured and deliberate.

The bass part consists of 60 synthesized bass phrases, each longer than the drum phrases. These are divided into 4 groups: building, fighting, winning, and losing. The latter two groups are chosen when the player is extremely close to victory or defeat respectively. Here are a few examples of these phrases:

Brough and I then worked together to tune the system - balancing sound levels of different elements, tweaking the phrase selection algorithm to best match the rising and falling action of the game, and working to process some of the original sounds to better blend with the new elements. Overall, our work resulted in a music system that closely tracks the drama and story of gameplay while staying true to the abstract, generative motif of the game.

Below is a video of some gameplay (of the tutorial level) to show the end product. (note: not my recording, found on YouTube).

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