PCI-E Spread Spectrum?

mojothehut

Senior member
Feb 26, 2012
354
6
81
Heya,
So I have a quick question about PCI-E spread spectrum in my sabertooth 990fx's bios.

Is there any reason to mess with it? by default it's set to auto. The little tool tip says disabling it may help overclocking?

Thanks :cool:
 

taltamir

Lifer
Mar 21, 2004
13,576
6
76
spread spectrum (for PC components) means that it will dynamically cycle clockspeeds up and down around the target figure to reduce the noticeable interference it causes with other devices.

Enabling it makes the system slightly less stable (should only matter if you OC and even then barely noticable) while reducing its MEASURED interference with radio signals under standard tests without actually reducing its ACTUAL interference with radio signals. This is done to exploit legal loophole and to remain compliant with FCC in the United States, JEITA in Japan and the IEC in Europe.

so bottom line is that you will likely never be able to tell the difference between it being on or off but its to your benefit to leave it off.

See: https://en.wikipedia.org/wiki/Spread_spectrum#Spread-spectrum_clock_signal_generation
Note that this method does not reduce total radiated energy, and therefore systems are not necessarily less likely to cause interference. Spreading energy over a larger bandwidth effectively reduces electrical and magnetic readings within narrow bandwidths. Typical measuring receivers used by EMC testing laboratories divide the electromagnetic spectrum into frequency bands approximately 120 kHz wide.[2] If the system under test were to radiate all its energy in a narrow bandwidth, it would register a large peak. Distributing this same energy into a larger bandwidth prevents systems from putting enough energy into any one narrowband to exceed the statutory limits. The usefulness of this method as a means to reduce real-life interference problems is often debated, since it is perceived that spread-spectrum clocking hides rather than resolves higher radiated energy issues by simple exploitation of loopholes in EMC legislation or certification procedures. This situation results in electronic equipment sensitive to narrow bandwidth(s) experiencing much less interference, while those with broadband sensitivity, or even operated at other frequencies (such as a radio receiver tuned to a different station), will experience more interference.
 
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