For generating (and measuring) audio signals, I can recommend
Spectrum Lab by DL4YHF.
It is free of charge, is updated frequently and has excellent support.
It can be configured to do most things concerning audio, also ultra
and infra sound.
I have used it to detect infra sound sub Hz, and I could easily
detect the movement of a door at the other end of the room,
with my laptop's internal electret microphone.
I also detected the propeller sound from the ferry, 10 min before
arrival in our fjord.
Tom, LB8X
