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  Why is Spread Spectrum Setting "Auto" Claimed to be More Stable? 
 
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john albrich Aug 07, 2012, 07:09am EDT Reply - Quote - Report Abuse
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Edited: Aug 07, 2012, 09:22am EDT

Replies: 6 - Views: 7221
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Can anyone explain why motherboard manufacturers are now advising us to always keep the Spread Spectrum (SS) option set to "AUTO"...especially when overclocking? (or point to an explanation by someone who really knows what they're talking about).

If using the "AUTO" Spread Spectrum setting now always "improves system stability" and it helps the system comply with regulatory agencies (e.g. FCC), why do they still even offer this as an user selectable option? That doesn't make sense.

On pre-7xx series AMD motherboards (e.g. before "ASRock 770 extreme3"; "ASUS M5A97 AM3+ 970", etc), if you wanted the most stable system when overclocking, you always DISABLED the "Spread Spectrum" option in BIOS Settings. Enabling SS in fact decreased system stability (but increased technical compliance with regulatory agency requirements).

Your option choices (when allowed) back then were
1.Enable SpreadSpectrum...2.Disable SpreadSpectrum
or
1.On...2.Off

With newer systems however, upon reading multiple different manufacturer AMD compatible motherboard user manuals, the manufacturer's generally advise you to always select the "AUTO" option. The choices are now generally
1.Auto...2.Disable

Not only is this not intuitive, nor do I understand why this would be so from a technical standpoint, I can't find an explanation on what has changed, or WHY selecting "AUTO" now supposedly provides the best system stability when overclocking.

I can't think of any condition in which overclocked system's stability would improve by activating SS clocking...and I would think it would be made even worse to have your system clocks vary between running SS some of the time, and being fixed frequencies at other times (which is what the "AUTO" setting suggests to me).

It would be much appreciated if someone can explain the technical reasons for this change.

edit to add:
I don't know if the same thing applies to Intel CPU compatible motherboards. I would think it should, but we may find this change is specific to a chipset found only on AMD compatible motherboards.


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Joshua Marius, LeThe Aug 07, 2012, 09:30am EDT Reply - Quote - Report Abuse
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>> Re: Why is Spread Spectrum Setting "Auto" Claimed to be More Stable?

I don't really listen or pay much attention to all of these theories that get published. When it comes to overclocking I tend to evaluate each case separately; even two PCs with identical specs can perform/behave differently. I'd just try it with both Disabled and Auto to see what happens. I think you'll spend more time looking for an exact answer (although I do see the purpose of this) than trying it out and making sure it's stable.

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john albrich Aug 07, 2012, 04:35pm EDT Reply - Quote - Report Abuse
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>> Re: Why is Spread Spectrum Setting "Auto" Claimed to be More Stable?
Joshua Marius, LeThe said:
...I'd just try it with both Disabled and Auto to see what happens....

Yeah...that's always a good thing to do in such situations. I just really want to know what's changed that adds more time and another variable to overclocking.

With the unpredictable nature of overclocking, I suspect if you OC 2 otherwise identical model motherboards, you might find with all other things being equal, one motherboard is more stable with SS "DISABLED", and the other is more stable with it set to "AUTO".

angryhippy Aug 09, 2012, 07:31am EDT Reply - Quote - Report Abuse
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>> Re: Why is Spread Spectrum Setting "Auto" Claimed to be More Stable?
Maybe they see the speed step crap as a form of overclocking and fearing some users wouldn't, they just have it set to auto to keep peeps from making the wrong choice. Maybe the default for auto has changed from enabled to disabled. Just a wild guess.

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Meats_Of_Evil Aug 10, 2012, 03:00am EDT Reply - Quote - Report Abuse
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>> Re: Why is Spread Spectrum Setting "Auto" Claimed to be More Stable?
I've always had Spread Spectrum on Auto, I don't know what the hell it does but it doesn't bother me enough to change it. When I began overclocking my Q6600 I had an idea of how much juice I could get out of the cpu so I didn't bother to change an other settings since the biggest limiting factor to me was the temps.


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Ed Smith Jan 09, 2014, 10:43pm EST Reply - Quote - Report Abuse
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>> Re: Why is Spread Spectrum Setting "Auto" Claimed to be More Stable?
Apologies for replying to an old thread, but there really isn't much of an answer here. As an old school OC'er, I've always turned Spread Spectrum off, as in the past, a fixed frequency was always more stable.

Sorry that I don't have a real answer, yet -- this is a part one of two posts, as I haven't turned Spread Spectrum on in years. However, while going through a new motherboard manual, I saw the statement that Auto (as opposed to Off) was "more stable" and I'll be testing this weekend.

Competing theories as to why manufacturers would recommend enabling spread spectrum:

1. They're lying. Spread spectrum doesn't make things more stable, but does help meet emissions requirements (FCC & others)

2. They're telling the truth. It's possible, given advances in chipset designs, that, when you OC the main clock, with spread spectrum disabled, certain clocks are locked at their rated speeds, and the ratios have to change. As the actual ratio varies from the expected ratio, instability might increase Alternately, it's possible that, with spread spectrum enabled (or Auto), as OC clockspeed increases, some secondary speeds may also increase, allowing ratios to remain roughly the same (or at least closer to normal). In some cases, this could be more stable. We don't really know what "Auto" refers to.

Lacking a good enough oscilloscope or frequency counter, all most of us can go by is stability. I'll post some OCing results, this weekend, when I have time to OC with Spread Spectrum in "Auto," as this topic is the closest search engine match to this question.

john albrich Jan 09, 2014, 11:50pm EST Reply - Quote - Report Abuse
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Edited: Jan 09, 2014, 11:55pm EST

 
>> Re: Why is Spread Spectrum Setting "Auto" Claimed to be More Stable?
Ed Smith said:
...
Competing theories as to why manufacturers would recommend enabling spread spectrum:
1. They're lying. Spread spectrum doesn't make things more stable, but does help meet emissions requirements (FCC & others)
2. They're telling the truth.....


I don't recall anyone specifically "lying"...I think it's just more of they just don't explicitly tell consumers why they provide spread-spectrum (end-goal is to reduce manufacturing costs and be more competitive, hence more profit).

I used to work in PC design and dealt directly with FCC compliance in the design, manufacturing, and testing arenas. As far as I know however, that was before the "Auto" option was implemented (hence my original question).

The only reason we implemented spread-spectrum was to reduce manufacturing costs. That allowed us to be more competitive and It allowed us to more cheaply meet the technical FCC requirements for "home" and "office" FCC emission rules. The "rule" of the regs if not the "spirit". TEMPEST is a whole other deal.

Anywhere a manufacturer can save a nickel or more in BMC (Base Manufacturing Cost) it's highly desirable (esp when you're talking about millions of units). Spread-spectrum could save multiple BMC dollars per unit, even after factoring in the cost of implementing spread-spectrum control circuitry and firmware.

Spread-spectrum allows manufacturers to continue to have relatively high RF emissions which SUBSTANTIALLY reduces the cost of manufacturing (reduces need for physical shielding, EMI "fingerstock" and "braid", wear-resistant plating and conductive paints (in the case of plastic cases), case fitment tolerances, case vent mesh, wiring shielding, cable RFI ferrite cores (clip-ons or permanent), and so on. If you look at pre-spread-spectrum PCs with plastic cases, you'll find some that used very thick copper and other metal-based painted coatings on the inside surfaces specifically to meet FCC regs...this was very expensive stuff and it required special handling and disposal during manufacturing (also added to the cost).

By simply spreading out the emitted RF energy over a wider frequency range in which peak and mean values were generated manufacturers are able to more easily comply with the RF band-specific FCC regulations.


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