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Device aggregation vs ADAT feed


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When using 2 MOTU boxes, is there any advantage to doing firewire device aggregation as opposed to using one box to make an 8 ch ADAT feed to the other (so 16 chan came from one box)?  It seems like in the latter case you'd have one less device on the FW bus, which would be a good idea, right?

Philip Perkins

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Hello Phillip,

Although the sample rate between two devices can be locked using a word clock, I have no idea in an aggregation setup how the devices would sync their buffers.

With this I mean that the MOTU devices send 512 samples in one go, but two MOTU devices would not do that simultaneously. One of them could be 50 samples off, or more. So although there would be no pops or clicks because the clocks are synchronised, it could be that there is a random (every time you boot up the system) latency between the two devices with a maximum of 256 samples.

However, the MOTU devices may be smart enough to listen on the firewire bus to each other and synchronise their buffers as well, but I don't believe so.

With a A/D converter connected to the ADAT input of the MOTU there will be a fixed latency that you would be able to compensate.

Anyway, I personally have a MOTU 828 MkII with a FocusRite OctPre connected via ADAT.

Cheers,

    Take

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I've always done the aggregation thing, but never more than 2 MOTU boxes, and never noticed a problem, but then again I wasn't looking for one.  One loss w/ the ADAT feed thing is that I wouldn't be able to include the digital inputs of a Traveler (feeding ADAT to a 2nd box) in the mix, which I've used as inputs 17-20 in some situations--the ADAT feed is just a conversion of analog inputs 1-8.  But I like not having 2 boxes on the FW bus on my old computer....  When I get a new computer I'll experiment w/ 3+ boxes and external WC.

Philip Perkins

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