How to generate new synthesize data (signals) ?

my work is to make a reliable lie detector, but unfortunately we face with lack of sufficient data, so we have decided to generate new data by synthesizing data which I already have.so far I couldn't find much about generating new data which look real!

I have some knowledge of how to make new synthetic data when it comes to image processing but my work is working with signals not images! please let me know if you have any suggestion on this particular work :)