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Someone mentioned a Sudden Motion sensor on my Mac causing dropped frames in Final Cut Pro....is this true?
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Yes.

PowerBook G4 computers starting with PowerBook G4 (12-inch 1.5GHz), PowerBook G4 (15-inch 1.67/1.5GHz), and PowerBook G4 (17-inch 1.67GHz) and iBook computers starting with iBook G4 (Mid 2005) have Sudden Motion Sensor technology, built-in protection for the hard disk that is designed to help prevent disk failures if the computer is dropped or undergoes severe vibration.

The Sudden Motion Sensor is designed to detect unusually strong vibrations, sudden changes in position or accelerated movement. If the computer is dropped, the Sudden Motion Sensor instantly parks the hard drive heads to help reduce the risk of damage to the hard drive on impact. When the Sudden Motion Sensor senses that the PowerBook position is once again stable, it unlocks the hard drive heads, and you are up and running within seconds.

In general, Sudden Motion Sensor protection does not change hard disk performance with regular PowerBook operation. Occasionally, the Sudden Motion Sensor may be activated by unusually strong vibrations at a time when your PowerBook is writing data intensively, such as when recording video or audio. Should you experience dropped frames or sound elements in such a situation, make sure that your PowerBook is in a stable environment without vibration or abrupt movement.

(Note that in some locations you may see the Sudden Motion Sensor referred to as the Mobile Motion Module. Both names refer to the same feature.)

If you have a computer with the Sudden Motion Sensor and you have video editing applications, such as Final Cut Pro, Final Cut Express, or iMovie that exhibit performance issues (like dropped frames), then temporarily turn off the Sudden Motion Sensor while working in those applications.

To disable the Sudden Motion Sensor:

First, find the current status of Sudden Motion Sensor:

  1. From the Finder's Go menu, choose Utilities.
  2. In the Utilities folder, open Terminal.
  3. When the command line appears, type sudo pmset -g and press Return.
  4. Type in the administrator password when prompted and hit Return. This command queries the computer for the current setting of the Sudden Motion Sensor, which you can determine by locating the ams entry (in Mac OS X 10.3) or the sms entry (in Mac OS X 10.4) and looking to the right to determine its value. The default setting is "1" (turned on).

Disabling the Sudden Motion Sensor in Mac OS X 10.3:

  1. In Terminal, which should still be open from the previous step, you can disable the Sudden Motion Sensor by typing sudo pmset -a ams 0 and pressing Return (changing the setting to a zero disables the module).
  2. Type your administrator password when you are prompted and press Return.
  3. Type the sudo pmset -g command again to be sure that the setting has been applied.

Disabling the Sudden Motion Sensor in Mac OS X 10.4:

  1. In Terminal, which should still be open from the previous step, you can disable the Sudden Motion Sensor by typing sudo pmset -a sms 0 and pressing Return (changing the setting to a zero disables the module).
  2. Type your administrator password when you are prompted and press Return.
  3. Type the sudo pmset -g command again to be sure that the setting has been applied.

Any changes that you make to the Sudden Motion Sensor setting remains in effect even after you restart the computer. If you choose to disable the Sudden Motion Sensor, Apple recommends that you re-enable it as soon as possible in order to take full advantage of the feature.

To re-enable the Sudden Motion Sensor:

First, find the current status of Sudden Motion Sensor:

  1. From the Finder's Go menu, choose Utilities.
  2. In the Utilities folder, open Terminal.
  3. When the command line appears, type sudo pmset -g and press Return. Type your administrator password when you are prompted and press Return. If you have the Sudden Motion Sensor turned off, the value of the ams entry (in Mac OS X 10.3) or sms entry (in Mac OS X 10.4) will be a zero (0).

Re-enabling the Sudden Motion Sensor in Mac OS X 10.3:

  1. If the above command returns a zero, you can re-enable the Sudden Motion Sensor by typing sudo pmset -a ams 1 and pressing Return.
  2. Type your administrator password when you are prompted and press Return.
  3. Type the pmset -g command again to be sure that the setting has been applied.

Re-enabling the Sudden Motion Sensor in Mac OS X 10.4:

  1. If the above command returns a zero, you can re-enable the Sudden Motion Sensor by typing sudo pmset -a sms 1 and pressing Return.
  2. Type your administrator password when you are prompted and press Return.
  3. Type the pmset -g command again to be sure that the setting has been applied.

Last update: 06:39 PM Sunday, February 19, 2006

 



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