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William W. Saunders, Jr.

Quick Latency Question - Using Extra Interface via ADAT

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Hi Cakestalkers,

I'm setting up a new Presonus Quantum with an existing ZOOM UAC-8 interface -- connecting via ADAT optical connector (yielding extra inputs for my old hardware synths).  Has anyone tested or does anyone know what sort of EXTRA latency I can expect between the arrival of an analog audio signal at the ZOOM's input and the ultimate output from the Quantum into Cakewalk for recording/monitoring?  I know the Quantum has near-zilch round-trip latency so I am primarily concerned with any extra latency imparted by the ZOOM during:

1.  Input signal to and through ZOOM's AD conversion, to

2.  ZOOM's ADAT output, to

3. Quantum''s ADAT input, to

4.  Quantum's Thunderbolt output, to

5. Cakewalk's recording channel

I guess I'm really just asking  if, in steps 1 and 2, the signal will incur ZOOM's usual latency (call it x) PLUS any latency added in steps 3 through 5 by the Quantum (call it z)?

Or will it be faster than (x + z) since the ZOOM doesn't really have to deal with any drivers or computer-related processing -- only its own?

Thanks,

Bill

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Latency is the result of the audio interface driver buffer setting and Plug-in Delay Compensation. There is only one audio driver in that setup.

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The speed of light depends on the media it is traveling through. It will be much slowing going through fiber (but still pretty fast).

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As Mr. Roseberry points, out, their ADAT A/D conversion is typically  under 1-millisecond of delay.  I have collected data about ADAT conversion latency for a couple of products that I own:

- The ART TubeOpto-8 is 32-samples A/D latency at 44.1k (ref: ART User Manual). 

- The Audient ASP800 is 39 samples (ref:  Audient tech support).

From that point onward, it's traditional to ignore any propagation delays in the fiber optics or wires because of the small distances involved.

To offer some pedantic info, signals propagate at about (Velocity Factor = light speed in a vacuum) 0.65-VF within fiber optic transport, and at about 0.95-VF for signals in copper wire.  Data rate is often confused with propagation speed and gets us into confusing discussions  about latency for audio.  My best thought experiment that helps to clear the air is to walk through the propagation delay issues that the Mars missions must endure.  No matter the data rate in kilobits or megabits, the propagation delays from Earth to Mars are an average of about 14 minutes each way; dependent on the relative positions of the two planet in their respective orbits.  Best case is about 4 minutes, and worst case is about 24 minutes.  

Okay, pedantic itch is scratched! Carry on! 

 

 

Edited by MediaGary
Fixed *wrong* autocorrects.

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I setup the following configuration:

Behringer ADA8000  -> (ADAT) -> Yamaha i88x  -> (ADAT) -> Focusrite 18i20

I couldn't perceive any difference in latency between a hardware synth plugged into the ADA8000 and it plugged directly into the 18i20.

I tend to be far more sensitive to latency when using piano sounds, so I was using a piano sound on my JV1010 and hardware monitoring enabled on the 18i20. This was to remove any latency introduced by the USB audio drivers. I couldn't perceive any latency at all with this setup.

On the other hand using a VSTi piano, a latency of 6ms was obvious. A 2ms latency with a VSTi, not so much.

What I didn't think to try was splitting the signal, so basically record the same thing through the ADA8000 and a direct connection to the 18i20 at the same time. 

The next time I get a chance to try this, I'll report my findings.

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