# Vertical versus horizontal frequency

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Hi all,Could someone please explain to me the difference between vertical (refresh rate) and horizontal (scan rate) frequencies? What does each do?

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They are related to each other basically.The horizontal refresh is the number of lines per second that can be drawn. There is some overhead to move back to the top of the screen after reaching the bottom (the 0.95 = 5%).The screen is X number of lines (640x480 or 800x600 or 1024x768 or 1280x1024 or 1600x1200)Vf= horizontal frequency / number of horizontal lines x 0.95 where Vf represents vertical frequency, or the maximum refresh rate.Take for example a Samsung 950b:Horizontal Scan Range: 30kHz - 85 kHzVertical Scan Range: 50Hz - 160HzMaximum Resolution: 1600x1200so we have 85,000 / 1200 x 0.95 = 67.29 HzMaximum Vertical Refresh rate 67 Hz.Now, same monitor, lower the resolution to 1024x768 and we get:85,000 / 768 x 0.95 = 105 Hz maximum.Now, just because the maximum is 105 Hz does not mean that it supports that rate, as you'll notice that the Horizontal frequency is a RANGE ...Now lets look at a higher end monitor:Sony CPD-G420SHorizontal Scan Range: 30kHz - 110kHz Vertical Scan Range: 48Hz - 170Hz Maximum Resolution: 1800 x 1440 Same math:110,000 / 1440 x 0.95 = 72Hz110,000 / 768 x 0.95 = 136HzNow that you know how to calculate the refresh rates, heres the important point of all this.85 kHz = 1024 x 768 @ 85Hz 95 kHz = 1280 x 1024 @ 85Hz 107 kHz = 1600 x 1200 @ 85Hz are pretty much the minimum horizontal scan rates that will give you acceptable (eye-pleasing) refresh rates. You will also find that in your spec hunting that these will pretty much show up in three different price ranges too. Although your monitor CAN display higher resolutions by dropping the vertical scan rate, you are pushing your monitor beyond what it is recommended to run at (you'll hear a very high pitched whine)Anything above 107kHz is in the if I won a lottery ticket, I'd buy ...Hope that helps you out ...Ray

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Thank you Ray, that is perfect!

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