this project is great!
after a quick research, it seems that esd might be a bit outdated now [1] and that more recent sound API could be used. it seems however to do the job just fine.
Yes, if people say that esound was already outdated by 2003, then by now it should be very much dead. But I was more focused on completing this project than on researching sound APIs, thus I simply took whatever Xoscope guys used.
After all, we simply want to read voltage level from simple input - why should we need to invent new library for it every 3 years?
[1] http://www.linuxquestions.org/questions/programming-9/esound...