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Warren,
I think the key is signal to noise ratio.
If you stacked the same frames the noise duplicates (and is reinforced)
along with the data.
In a set of different subs, the noise tends to be random and is therefore
rejected as noise in a stack while the data is reinforced as true data.
The more frames you stack in theory, the more the noise 'drops away'
down to a mathematical noise floor.
You reach a point though, eventually where you gain nothing more by
adding frames....
Someone better versed in the maths can help out here.
Hope this helps,
Steve
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