TIMING: Why external validation of the Display is needed [25718]

This article applies to:
E-Prime 3.0
E-Prime 2.0

E-Prime 1.x

 
Detail

Unlike CRT monitors, LCD monitors do not use the raster technology to redraw the screen. In E-Prime, most displays are synchronized with the vertical blank to avoid partial screen displays and to provide accurate timing. The vertical blank is determined by the position of the raster. Without being able to judge the position of the raster, PST cannot guarantee the synchronization of each display, nor guarantee that the reported refresh rate is accurate.

For this reason, PST recommends the use of a device such as Chronos with a Photo Sensor to verify refresh rate as well as latency. Testing of the refresh rate and latency can help determine if the monitor is caching the screen for example.

NOTE: Issues can be due to the hardware, video driver, or the Operating System. In general, it is best to start with updating the video card driver if you encounter issues with your monitor.

For example, PST has found with the monitor below that the screen was double refreshing when the "Activate Windows" watermark was on screen (i.e., drawing E-Prime then drawing the watermark over E-Prime). This resulted in delays with the copy.

The timing itself was good but could have increased the duration of E-Objects since Windows had to draw over E-Prime.

NOTE: The above example was staged for demonstration purposes. Psychology Software Tools, Inc. always recommends running in a valid supported Operating System.

The majority of monitors we encounter act more with how a CRT behaves. In the data below, we see the refresh rate and latency line up with what we expect.

For example, we see E-Prime's and a third-party monitoring line up under a millisecond:

The Photo Sensor from Chronos tells us the hardware latency of the monitor. We can see in the image below that we have a latency of ~4ms:

For more information on how to test your hardware and machine, see the links below.

 See Also:
TIMING: E-Prime 2.0 Monitor Recommendations and Timing Information [18080]
TIMING: Verifying your Clock and Timing in E-Prime [34371]
Benchmark for Graphics and Monitors [29932]