Estimating the speed of sound with stereo microphones and Audacity

Screenshot from 2014-01-13 22:43:03With a pair of binaural mics placed 33.7 cm apart feeding into a stereo USB sound card (a Griffin iMic), I clapped near the left mic. It took 39 samples (884 µs) for the peak to travel between the microphones. That gave me a speed of sound of 381 m/s. A bit high, but the conditions this evening weren’t ideal, and I only set up the experiment with cursory care.

The iMic seems unusual in having a stereo line/mic input. Most other (cheaper) USB dongles only have a mono input.

the analogue hole

I have a bunch of Catherine’s old family recordings to digitise (do people still do that – sit around a tape recorder and make recordings?) and I had recorded one of Ken’s shows on minidisc, so I needed a relatively clean way to get analogue audio onto the computer.

I ended up getting a Griffin iMic, a small USB audio input device. The sound quality is remarkably clean; here’s a sine wave recorded from CD to minidisc, then recorded on the iMic:



The  iMic seems to work with all Mac audio software as an input device. The free Final Vinyl recording sofware is pretty, but a bit buggy and annoyingly, only works when the iMic is connected. I just use Audacity, and have done with it.