how do you record audible sound, and play it back as infrasound ?

If this was on a file, you could use sox on Linux. It may even be able to use sox in streaming mode.

Best,

Erik

Experiment. examining the range of corvid hearing. I'll need to do the same with ultrasound.

Is your recording analog or digital? If it is digital, you will need some signal processing SW of some sort to downconvert the recording to infrasonic frequencies. If it is analog, you would have to use some sort of frequency downconverter (heterodyne).

Of course, either way, it will no longer sound anything like the original recording so I would ask, why are you trying to do this, or what are you trying to accomplish?

I'm not quite sure I understand the question, but... Assuming the recording is digital, any DAW can lower the pitch of a recording with or without changing the tempo. Altho, going all the way down into the infrasonic range, I dunno...