So what does an action potential look like? As an answer, you may point to figure 15. But the reality is a bit more complicated, because filters with a non-linear phase response may distort the signal shape you see. Whenever you filter a signal, make sure that you are aware of what type of filter you are using and in what specific way.
A great resource for learning about filters and audio processing is Stanford's CCRMA page: https://ccrma.stanford.edu/~jos/filters/filters.html
The topic of filters distorting signals and their potential ability to make artifacts look like spikes have been covered by Quian Quiroga[Quiroga 2009]
[Quiroga 2009]Quian Quiroga R. What is the real shape of extracellular spikes? J Neurosci Methods. 2009 Feb 15;177(1):194-8. doi: 10.1016/j.jneumeth.2008.09.033. Epub 2008 Oct 14. PMID: 18983872.