Weird note structure on guitar audio waveform Why do some times notes take these weird structures (circled below). That is a guitar monophonic audio waveform by the way (3 note melody).



There are 3 notes played in this audio file. These are the beginning of the waveform (0), around sample 52000 and around sample 95000.

My two questions are:


Why did this weird looking negative amplitude peak get created (circled)?
Right after the final note (where the arrow is), why is there such a big change in amplitude (down, up, down again)?


The audio file is here.
Here are some possibilities:

Transverse waves on a guitar string have two polarized components, one parallel and one perpendicular to the guitar's soundboard. User hotpaw2 mentioned energy exchange. It is imaginable that energy transfer could happen between the components. The component parallel to the soundboard is largely inaudible, so it could stealthily store energy until released later.

Or it could be that you have two strings with modes that are slightly out of tune, and they form a beat frequency.

EDIT: Having analyzed the audio sample, the things you have marked are just some low-frequency artifacts, I think from things like someone touching or shaking the mic or moving around and bumping the guitar body. Adding a 100 Hz high-pass filter mostly gets rid of those:

Figure 1. Sample after 100 Hz highpass filtering.