The Sudden Motion Sensor Hates Your Mobile Session

Lots of laptops use an accelerometer to detect that the computer is falling. When that happens, the computer parks the hard drive heads to prevent them from bouncing on the HD platter. Apple calls this the Sudden Motion Sensor. On Thinkpads it's the Active Protection System. Other laptops have similar features.

The problem is that loud sound can trigger the accelerometer and park your hard drive heads. For audio work, especially during takes, this is very bad: when the drive is parked, you can't write to it, and when you can't write to disk, you can't keep recording. On Pro Tools you'll get an -9073 error; on Cubase and Nuendo you'll get a dialog that says "Recording Error: Too many tracks recording."

I figured this out after years of frustration -- I often track with a laptop in the same room as hundreds of watts of angry tube amps, and during those sessions I had repeated, mysterious problems with Cubase dropping out of record. Learn from my pain: At a bare minimum, disable the motion sensor for any tracking work.

On a Mac, disabling the Sudden Motion Sensor is easy:

Start Terminal (in /Applications/Utilities) Type sudo pmset -a sms 0 and hit enter Enter your administrator password

Then to re-enable: sudo pmset -a sms 1

I'm still doing some testing to confirm that this solves my problem, so please report back if you try it!

Here's the last time I got bit. My laptop was three feet in front of the Marshall cab.

(There's a longer version of this post on my personal blog.)