FYI, it supports decoding ultrasound wav files. I use a Dodotronic UM250K mic to capture ultrasound up to 125 kHz. LCD monitor and other electronics emits some interesting sounds. For some reason, getUserMedia doesn't allow high sample rates, but ffmpeg works:

ffmpeg -f alsa -channels 1 -sample_rate 250000 -i hw:CARD=r4,DEV=0 -t 5 mic.wav

That Webfft is fun. Try recording yourself making a few long vowel sounds A I U E O AE UH , and take a look at how the harmonics/formants/ the pattern of peeks at different frequencies is distributed between sounds.