Onset detection - it's tricky business

I ran into some complications with extracting some notes. The instrument I was looking at was the Double Bass. The IOWA file can be found here.

Here's a demonstration of the problem encountered.











Taking a closer look at note 'G' :



The spurious peaks detected in the audio sample proved problematic for my algorithm. I suspect that this being an 'arco' sample, the problem could be due to vibrato?? Anyway, my work around involved adding more thresholds. I noticed that there tend to be short periods of non-peak activity in the actual notes themselves. This was causing some confusion. To overcome this I added a min-gap time threshold so these gaps would not interfere. It took a while! So to continue and no doubt, there will be other issues. I'm still to get started on the front end...!