Beat analysis for game visualization

One of the algorithms we chose to implement was a beat detections algorithm. In the game this maps to a pulsing visualization.

Background

When a drum is hit, a spike in energy occurs across all frequencies. When a bass guitar is plucked, there is a spike in energy in the lower frequires. As these two instruments are commonly used in modern music to give a song rhythm or a beat, we decided to look at energy in the lower end of the spectrum. Theoretically, this should automatically filter out other spikes of energy created by a vocalist or electric guitar.

Beat detection on metric's "gimme sympathy"

Beat detection on flogging molly's "don't shut 'em down"

Using energy comparisons to detect beats

Energy calculation

Constant calculation

Filtering extra beats

If a beat is detected, its sample number is recorded in a vector. If a beat spikes for multiple samples, multiple beats would be recorded which leads to an overestimation of the current tempo. To account for this, we merely look at the samples, detect a leading edge where the first beat is recorded, and ignore all subsequent sequential beats.