Vertical
Refresh Rate
Definition
Vertical Refresh or Refresh Rate in interlaced* mode this
is the number of fields written to the screen every second.
In non-interlaced mode it is the number of frames (complete
pictures) written to the screen every second. Higher frequencies
reduce flicker, because they light the pixels more frequently,
reducing the dimming that causes flicker.
Measurement
Expressed in Hertz* (Hz), this represents the number of
frames displayed on the screen per second. If there are
not enough, the intervals in between will be observed resulting
in a flickering display.
Flicker-Free Performance
In order to achieve a flicker-free display, it is best that
a monitor have a refresh rate (VSF) of 75Hz or above. A
computer's graphics circuitry creates a signal known as
the horizontal scanning frequency* (HSF) or scan rate. This
signal is based on the Windows desktop resolution and Refresh
Rate. (See Formulas below on how to calculate this.) To
support sharper images at higher resolutions, a higher scan
rate is necessary. VarTech offers some multi-scanning* or
"autoscan"* monitors that will lock on to any
signal that is between its minimum and maximum Horizontal
Scanning Frequency. The signal will not be displayed if
it falls out of the monitor's range.
Formulas
VSF = Vertical Scanning Frequency (Refresh Rate)
HSF = Horizontal Scanning Frequency. (Scan Rate)
Maximum
Refresh rate:
VSF = HSF ÷ number of horizontal lines x 0.95
Example:
Horizontal
Scanning Frequency = 85kHz
Resolution
= 1280x1024
Maximum
Refresh Rate: VSF = 85,000 ÷ (1024 x 0.95) = 87Hz
Horizontal
Scanning Frequency = 85kHz
Resolution
= 1600x1200
Maximum
Refresh Rate: VSF = 85,000 ÷ (1200 x 0.95) = 75Hz
*More Definitions
Hertz - the number of times something happens a second.
Interlaced
- Scheme to display a video image by displaying alternate
scan lines in two discrete fields.
FPS
- Frames Per Second: an expression of frame rate.
Horizontal
Scanning Frequency - Indicates the speed, measured in
kilohertz (KHz), at which a single horizontal line is drawn
on the screen.
Multi-scanning
- A monitor's ability to change resolution or refresh rate
when signalled by a video adapter. Graphics adapters have
the ability to "tell" a monitor to use various display
resolutions and refresh rates. If the resolution or refresh
rate is within a monitor's scanning range, multi-frequency
monitors adjust to the resolutions and refresh rates "ordered"
by the video adapter.
Autoscan
- A microprocessor-based feature of some monitors incorporating
automatic
synchronisation of their horizontal and vertical frequencies
with those of the installed video graphics adapter. An autoscan
monitor can thus operate with a wide range of video adapters.
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