Setting up a BPM detector using the analyser is possible but it would be quite complex. If you are creating the music and you know the BPM and when it varies, I would suggest that a better option is to use an array that is populated with the 'Beat Intervals' for each song and then use that in combination with the timer behaviour to trigger your spawns.
e.g.
Array(Beat Intervals):
.44
.44
.44
.44
.52
.52
.52
etc.
On Music Playing - Trigger Once:
- Start timer "beat" for Array.Front (once only)
- "Array" Pop Front on X axis
On Timer "beat"
- Start timer "beat" for Array.Front (once only)
- "Array" Pop Front on X axis