Which sound is knocking ??

Audio knock detection would take time to get use to knowing which sound to pick out of the recording . First time I have herd audio knock detrction . Seam to me it sounds as if knock is accuring when it sounds statically . In the clip kinda like an old stereo system when a thunder storm is near by and you get a crackleing noise in the speakers if listening to over air broadcast .

Although the HPA stuff is great, I found the recordings here handy as well - http://theknockbox.com.au/the-knock-box/sound-recordings/