I have never seen this before, and it starts out with one strike against it, since it spells bus wrong, but I was guilty of that for a time, before I figured out what the right word is in the context of combining signals, and what the wrong word really means (look it up).
OK, from a quick glance at the article I see several claims that jump out at me.. Since the document is copyrighted I will paraphrase.
#1 The more inputs to a system the more losses. (pg 3)
That may be an awkward way of relating the increasing noise gain of a "lossless" (not my nomenclature) virtual earth summing system, but as I published a few decades ago, there are other ways to skin that cat without the linear increase in noise gain.
#2 twice as many inputs = twice the bus noise.. (pg 5-6)
The math is a little sloppy as incoherent noise sources do not add linearly, but my larger criticism of the comment is that source noise will still dominate console noise, even for large consoles (I have designed at least one console with 100+ feeds to L/R bus).
#3 digital combining cost 1 bit of (?) for every doubling of stems. (pg 7)
I'm basically an analog dog, but I do enough digital crunching to know that is nonsense. Simply adding together multiple digital signals results in the exact same digital word resolution. Headroom or bus overload is exactly the same as analog, but digital can use a carry bit to buy another 6dB of dynamic range transiently.
If you combine with a multiply (digital fader/pan gain adjustments are preformed by a multiply) You actually gain resolution in an output digital product with even more bits! In fact the result will have the bit resolution of the input word, added to the bit resolution of the multiply word, or more bits than we can typically use or care about.
#4 Dither?
This seems to be a red herring, Dither is pretty well understood by now (I think).
#5 A mix of 64 sources needs to run -36dB (pg 8 )
Again. sloppy or misinformed math. Perhaps for 64 identical sine waves but 64 incoherent sources only increase +18 dB, and we don't build mixes with 64 inputs all at full gain, all the time.
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Sorry, this paper reads like a marketing tout masquerading as technical information so caveat lector. I really wish a fraction of those claims were true, because if there was a real benefit to mixing in the analog domain, I would have the technological edge to promote (my current source summing).
I have been searching for some actual critical flaw in digital combining for years and I haven't found it yet.
I would take this paper with a grain of salt (the size of a deer lick).
As I have said several times, there are real performance consideration when combining a large number of analog stems, but noise is not the dominant one (distortion and phase shift are real consideration on the scale of that paper's comparison). Digital on paper at least, seems to have the edge.
JR
PS: For the record I have nothing on sale here. I have been out of the console/mixer business for more than a decade, and I see little reason to promote a technology that has been eclipsed by digital. I still have friends making and selling analog consoles but they don't resort to such merchandising.
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Topic: S/N in big consoles (Read 34840 times)