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Understanding the concept and limitations of independently counting timecode.
We have seen that the use of a 24 hour real time stamp has many benefits, one of which is the non-repeatability of the timecode. There is and always will be only one value for any given date and time. This unique time reference thus becomes the common denominator that synchronizes all Aaton and SMPTE devices on set.
On paper, the concept is simple and elegant: if all devices on set contain highly accurate clocks recording the identical date and time, then the associated image and audio can be synced to one another by referencing the time stamp rather than the clap of a slate.
In the real world, however, it is important to take a few precautions to enable the system to work as such.
For the purposes of audio sync, Aaton specifies that cameras, recorders and other devices remain accurate within 1/2 a frame to one another at all times.
Today's technology allows for the development of extremely stable temperature compensated electronic crystal systems to control the internal timecode clocks to a high degree of accuracy.
A ppm (parts per million) rating is a measurement of the accuracy you can expect from a particular timecode device over time. The lower the ppm number, the more accurate the device. The more accurate the device, the less timecode drift will occur over time.
Here is a chart listing the manufacturers' specifications of the stability of their internal timecode
Denecke Ambient GMT 1 7-8 hrs Any device w/ GMT 1 7-8 hrs
As you can see from the chart, the accuracy of the crystal used in all Aaton cameras and timecode generators, as well as the crystal used in a growing number of DAT recorders (such as the HHB with MS1000 timecode module) is rated at 1ppm. This translates to an accuracy of approximately 1/2 a frame drift or less over 7 hours.
Ideally, the better the ppm rating of all equipment on set, the more time you can roll before the need to re-initialize. In a timecode environment, remember that your estimated time between re-initialization will be dictated by your weakest link.
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