Today, I starting with NPTEL lectures on acoustic instabilities in aerospace propulsion by Dr. Sujith IIT Madras. When started to take notes, I just found that I don't have a notebook. As I don't want to take the momentum away. Rushed to the walmart to buy a notebook. They are too pricey..commonn an A4 sized 100 pages notebook is around 4$. That's crazy compared to my home country. So coming back to the acoustics, the course starts with an introduction to acoustics. One dimensional wave propagation. later on combustion comes into picture.