Quote:
Originally Posted by dkatz42  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.
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. |
Ok...I tested the SSL-rig and my old Protools mix system by going analogue out and back in again.
The difference between the new and original files were just below 2.0ms on the ssl and just above 2 ms on the protools.
However when I was playing bass through both systems it was obvious that the ssl was slower (yeas, I am extremely sensitive towards latency or deviations from linearity of tempo etc , ok? ;-)) than the protools rig.
I then played the originalfile, on the ssl, out analogue 1 and back in analogue input 2, recorded on that track and routed it out analogue 2 into analogue in 3 and recorded that track at the same time. Now the difference between the original and track 2 was still 2 ms but between track 2 and 3 it was 5.3 ms....now how is that?...
On my protools rig it was 2.0x between original and track 2 and 2.0x between 2 and 3 and onwards...
My translation of that is that 3.4 ish ms were added by logic because when it was recording material that wasn't buffered (which is the case of the playback of track 1 but not the "play through" on track 2 while recording) it took some more time.
Hence 5.3 ms being the more accurate calculation of the actual latency of my fingers hitting the strings to the sound coming back out of the speakers....
So..anyway....yes the ssl's roundtrip latency was 2ms to , in and out of analogue, and back from the alpha link ....
Tomorrow I will perform the same test on the symphony rig. Since I can feel that the latency on it is worse than the , brand new I must add, Madi extreme-Alpha Link I would be surprised if the numbers showed me anything else...