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Pit Lenz

I did some latency tests and found out a strange behavior of the groups:
I found out that monoGroups 1/2 and Grps 17/18 (in a 18-monoGrp-setup) and stereoGrps 1 and 9 (in a 9-stereoGrp-Setup) seem to have a delay of 4 samples.

Here`s the test setup:
GLD V1.02, Rev. 5638
I started with a default FOH show and put up 9 stereoGroups in one show, 19 monoGrps in another show.
Both shows can be downloaded to check for yourselves at http://www.pitlenz.de/public/AllenHeathGLD.zip

Now I hooked up a white noise generator (from AudioTools) on channel 45/46, because small sample delay differences can be easily detected with white noise. If there is a delay, you`ll clearly hear a coloration in the sound.

Now let`s take scene #1 of the “9StereoGrps” show. (allGrps straight, no delay).
WhiteNoise at Input45/46 is sent to all Grps, all Grps are routed to L/R. Everything`s straight, no EQ, nothing delayed. We listen to L/R in the headphones and active speakers.

Let`s turn up Grp1: WhiteNoise is clear. Grp1 stays up, we add Grp2 : Noise gets fuzzy. Now check all the Grp combinations. Any Grps from 2 to 8 are OK with each other, the sound is just alike to one single open Grp, just louder. Good! But if we combine any of Grp 2-8 with either Grp1 or Grp9, the noise gets fuzzy!

Now let`s turn up Grps 1 and 2, select Grp2 and go to Processing/Delay. Start turning up the delay time of Grp2 and at 4 samples the noise is clear just as it is between G2-8. Let`s set a delay of 4 samples ro Grps 2-8.
Now ALL of the groups are time aligned, but 4samples late (This is stored in scene #2).
That`s OK, as long as we mix ONLY through groups and nothing is routed directly to L/R. (This option is shown in scenes #3 and #4).

In scene #3 ( Direct to L/R AND to un-delayed Grps) we can combine Grps 2-8 with the direct signal without coloration, bus as we put up Grp1 or 9 WITH the direct signal, the white noise gets fuzzy again.

In the second show (18monoGrps), the four Grps 1/2, and 17/18 behave just as their stereo combined versions in the StereoGrp-show. Any of these can be combined with each other but not with Grps 3-16, as thery are late by 4samples again. Delay them (scenes #2) and they are aligned with each other, but not with the direct signal (see scene #4).

Now comes the FUNNY PART:
PFL signals behave differently, but ONLY on monoGrps 1/2 oe stereoGrp1, NOT on StereoGrp9 or MonoGrps 17/18!
If nothing`s delayed (scene #1) and the combination of stereoGrps 1 and 2 sound fuzzy, their PFL signal combined sounds OK.
If we delay Grp2 to timealign to Grp1, our mix sound OK but PFLing both sounds fuzzy now!
This is not the case with stereoGrp9 (or monoGrps17/18 in the other show). Here PFL gives the same result as the mixed output.

This is quite confusing, maybe someone from A&H wants to chime ine to shed a little light on this….
If you want to listen to this for yourself, check out the files, use a WhiteNoise generator hooked to Input 15/16 and report your results.

Greeitngs from Germany