[Homeroast] Iphone app for determining inaudible crack sounds

Allon Stern allon at radioactive.org
Fri Apr 9 15:12:12 CDT 2010

On Apr 9, 2010, at 3:56 PM, Bonnie Polkinghorn wrote:

> I think the thread was called Hearing cracks, aka. I did it, started by
> Pecan Jim.  It said, further down in the thread, by Samuel Goldberger, that
> it's a $4.95 app.

Actually, I started it off 12/13/2009 in the thread "Seeing First crack"

Here's a repost:
So, in my quest to build a roaster (someday), I have thought, how useful would it be to be able to detect the cracks?
Well, that remains to be seen, but the other day, I was at a party and ran into a friend (and fellow homeroaster) who showed me an app for his iPhone, that I immediately went and downloaded. It is an audio spectrum analyzer which gives a waterfall display. Now, the accuracy of the iPhone's built in mic leaves much to be desired, but it's an interesting tool nonetheless.

Anyway, here are some spectrograms of my HG roast of 250g of Oriente:


Blue is low level, red higher level, and white is higher still. There is a frequency scale on the right which is largely obscured, but more visible in other spectrograms I took. The first crack is shown in the middle, to the left and right is where I was shaking the fry basket and bowls that I use to roast in. The red background is the noise of the heat gun.


More cracks are visible. Again, on the right is where I shook the basket.


Here I turned off the heat gun and coasted a little bit before starting cooling.

For the uninitiated: See: http://en.wikipedia.org/wiki/Spectrogram


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