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Originally Posted by figgebass  I don't really get it...are you telling me that the rosetta is what's causing the latency since you say that the symphony card has "virtually no latency"?
I'm not so sure...
Here's the apogee page: Apogee Electronics > Products > The Symphony System where it says that the symphony system has a latency of 1.6 ms at 96 khz.
Here's the page of the ssl madi extreme -alpha link that has 0.9 ms round trip latency at 96: Solid State Logic | Music |
My father years ago gave me a book called "how to lie with statistics."
There are apples and oranges here. The spec on the Symphony "system" includes the (presumably) best-case latency *including the A/D/A conversion*. They are unclear as to exactly which converters provide the 1.6 figure (thus my guess that the Rosetta perhaps had higher conversion latency than the 16x.)
The SSL is MADI-to-MADI, which does not include any A/D/A conversion. You have to add the converter latency at the other end of the lightpipe to the figure to get a realistic latency number.
My comment that the Symphony card has "virtually no latency" is because it does almost nothing--it's a digital pipe and I'd bet that the time to get samples across that card is measured in microseconds. The latency associated with the card comes almost entirely from the buffering necessary to give the system elasticity--the bigger the buffer, the more leisurely the rest of the system can be about delivering samples, at the cost of latency.
And of course the conversion latency has to be added to this.
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To calculate what the symphony latency at 44.1 would be you'd have to add a little more than 2x1.6 resulting in what, 3.5 or so....if then the rosetta converts a bit slower than the Alpha link then I guess ....but at the same time I don't quite understand where the 5.7 ms comes from that my core audio driver states when I select symphony in the menu....
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Keep in mind that the Core Audio figure is that which the driver reports to CA. In particular, the SSL driver cannot tell what the conversion latency is at the other end of the MADI link, since it doesn't know what kind of equipment is there. The Symphony driver knows what kind of box is connected to the bus, so it can take the converters into account.
I'm a thousand miles from my rig, so I can't compare your numbers with mine (with 16Xs). But it should be relatively easy to measure the latency with an oscilloscope. My hunch is that the SSL numbers aren't really accurate, because they can't be.