1 (edited by Clint Goss 2022-08-29 17:13:31)

Topic: Latency on Hardware Loopback

I am wondering if there is any latency if I use a hardware loopback (a wire) on an ADAT port.

For example: I have a route in TotalMix from:

   AN 7/8 IN to AN 1/2 OUT

... that should have the latency of the ADC and the DAC - around 5+7 samples on the UCX II.

If I add an intervening route ... making it:

   AN 7/8 IN to ADAT 7/8 OUT to ADAT cable to ADAT 7/8 IN to AN 1/2 OUT

... would the latency increase?

Motivation: the reason I'm looking to do this is because I need to control the level of one AN 7/8 input going to two different outputs from a MIDI Source. The MIDI sequence to select the two outputs is quite slow (around 100ms) and constantly selecting the two output channels and changing the level of the input channel for that output as the knob is turning is far too slow / laggy. With the setup I'm describing using the physical loopback cable, I could (hopefully) control both target outputs by selecting affecting just the single output fader for ADAT 7/8.

This scheme would only be useful if there is no added latency ...

2 (edited by ebulb 2022-08-30 01:24:52)

Re: Latency on Hardware Loopback

ive never used it but wouldn't mirroring submixes work for this  ?  otherwise maybe fader groups would work ? select first output and add the fader to a group, then select second output and add the same input fader to the group again ? I cant recall if fader groups work across different outputs but I seem to recall doing something like this in the past (I think)..

Otherwise I'm not sure if the ADAT would add latency, but I think you could probably setup a test to see... for example with your ADAT loopback example you could also route AN 7/8IN directly to AN 3/4OUT...  then you have AN 1/2 OUT with the ADAT loop and 3/4 OUT without the ADAT.. if you ran them both into another analog mixer you should be able to hear the difference or flip phase to get an idea. you could also record both those outputs in a DAW to see latency difference etc..

Re: Latency on Hardware Loopback

Thanks for the info!

Mirroring submixes is not exactly my issue - in fact the submix of the two output channels I'm controlling are different ... but I need to affect the feed from one of the source input to both those outputs.

I don't think Fader Grouping will serve me either ... I'm actually affecting the same fader in two different submixes.

> I think you could probably setup a test to see

Yes, but it takes me many hours to set up a proper latency test (I've done about 20 such tests in the past). Was hoping to get a read on the theoretical latency before I go down this path. In my experience with RME, the "theoretical latency" is often accurate with real-world tests to the sample!

4 (edited by ebulb 2022-08-31 08:54:23)

Re: Latency on Hardware Loopback

Clint Goss wrote:

I don't think Fader Grouping will serve me either ... I'm actually affecting the same fader in two different submixes.

have you tried it though ? faders are added to fader groups based on their selected subgroup.. i dont have my UFX nearby right now to test but i just opened the iPad app and it worked as i recalled and the faders maintain volume ratios (as expected)..  the only thing this doesn't solve that i can see from your question is if you needed to vary the level ratio of 7/8 in each submix at different times.. but i dont think the ADAT cable solves that either ?

Clint Goss wrote:

Yes, but it takes me many hours to set up a proper latency test (I've done about 20 such tests in the past).

it takes you many hours to setup a loopback latency test ? isn't it just a couple of cables and some basic DAW routings, play and record.. ? that's all I was referring to anyway..

Re: Latency on Hardware Loopback

I just did the ADAT loopback test, and the results are as reported by RME documentation. The cost of a physical ADAT cable routed through TotalMix should be 6 samples (tested at 48kHz).

Here's the diagram which gives the specifics ... hope I've got all the specifics straight:

https://Goss.com/img/LatencyTestCG_23_ADATLoopback_2022_0911a_200dpiC10.jpg