Analyzing musical concert seismics
Hi
So we did a fun thing and recorded a concert in the university with geophones and are now analyzing the data (1000-3000 people, outdoors, around 20 triaxial geophones planted in grass in a around the venue (see picture), 500 Hz sample rate, velocity model should be 300-500 m/s).
Our biggest hopes and dreams were separating crowd movements from PA and music but we're still very far from that.
Right now we're trying to detect song starts and BPM using both STALTA and spectral analysis, similar but not exactly like that one Taylor swift concert paper and trying to use song starts to measure correct distance between geophones in hope to locate the major signal sources (stage PA and crowd mass).
- STALTA results show major time delta between near geophones (scale of 0.05s) and sometimes geophone closer to the stage see the first peak significantly later than further ones. How would you make sense of these results? (sta: 0.1s, lta: 10s)
2.. An open question for anyone interested - how would you go about this? Which tools and algorithms would you use?
To detect BPM we tried to autocorrelate single geophone traces checking the lags that match musical bpm (50 - 180 bpm so 0.3 - 1.2s) and locating the highest peak in the range - some songs were a dead match so the studio version bpm, some were half or double and some were wrong, we haven't gone through the meticulous process of using all geophones yet but did find that sometimes the entire spectrum yielded a more accurate result and sometimes focused bands under 50 Hz were best.
What is the best way to differentiate PA and crowd-based signals in a rather noisy recording? especially when the crowd was much smaller comparative to previous works in the field (the geophones were also closer in our case).
Do you think paved roads between the signal sources and all geophone and terrain height differences between the stage and some geophones are a significant hindrance?
Geophone geometry: before you come for us about the geometry keep in mind that like every good field work, we had some issues with production and the law and had to compromise our array.
Thanks to anyone that read all the way!