I'm implementing a gunshot detector following the article "Algorithm for Gunshot Detection Using Mel-Frequency Cepstrum Coefficients (MFCC)" (paywall).
In the article, the authors uses 22 features based on MFCC (coeficients normalized between 0.1 and 0.9). One of the features is "Standard deviation of fundamental frequency". I already spent all my day trying to figure out the proper way to do this calculation.
The expected value for a gunshot is near 0.04.