Stereo Outputs Phasing Issue

[JMO]

Hello all,

2 outputs (mix 6 output, mix 10 output) on a QU16 seem to be slightly out of phase with every other output of the console. I read something about this on a forum here today about the Stage Box having a bug in the software where some latency was created on one of the stereo outputs. I proceeded to reset the console and update the firmware (Qu16UpdtV1_90_4537.QUU) on it again but with no success.

The outputs are not completely out of phase (tested with a phase flip adapter), it seems more likely it is a latency issue. Mix 7-8 Has no issues and if I pair lets say output 5 and output 8 together there is no phasing. The Outputs themselves sound fine, short of breaking out a smaart rig.

Let me know if there is any solution out there,
Cheers,
Jeremy Moffitt

[Anonymous]

Can you measure the phase? Use a couple of short cables and run the outputs into channels 1-10, then QuDrive record and compare wave forms

[Giga]

That wouldn’t be accurate enough would it ? He’d have to also redirect the mains through 2 separate channels or am I missing something ?

Giga

[JMO]

I don’t know that a visual representation of the latency is going to help me in this instance, unless the amount of latency pointed me in a certain direction. However, because winter months have fallen upon us, I may just bust out Smaart tomorrow and take some measurements for the heck of it.

Thanks for the responses so far!

Cheers,
Jeremy Moffitt

[GCumbee]

You sure there is no EQ or delay on any outs when you test this?

[JMO]

I reset the console and updated the firmware. No eq, no delay on the outputs, the two problems are on stereo outputs as well. As far as I know any EQ/delay on an output on these boards are linked. Either way, there is none in use today!

[JMO]

Hello all,

Today I set up Smaart and have taken some screen shots. I’ve attached the screen shots so you can see for yourselves.

It appears the on-board pink noise generator is suspect to creating phase issues within outputs on the console. The mix outputs themselves are actually not coherent in relation to one another. For example on the QU16 and the QU24 (tested one just to be sure), Mix 1 and Mix 5-6 are not aligned but Mixes 1, 2, 3 and 4 are the “same” alignment. I don’t use the QU series frequently enough to say if it really matters or not that separate mix outputs have different phase alignments, its not a large format desk, but I can say it is very good news that the stereo outputs do share the same phase.

At the end of the day, if you’re carrying a QU16 or something for a traffic desk at a festival or arena, don’t use the generator to Smaart your rig. Makes me want to go run and buy my own tone generator right now!

Learn something new everyday.

Cheers,
Jeremy Moffitt

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[Giga]

I have a very basic understanding what Smaart is used for but not enough te be able to interpret the graphs. Care to explain ?

Also, why is it a problem if some outputs aren’t totally in phase ?

Giga

[JMO]

The Left side of the screen is using a reference from a MR1 Audio Generator. Its comparing a direct signal from that unit to a signal which has split from that unit, to the console, and routed to every output on the desk. I can find the delay time between the direct source and the measurement source (which is the console output) and then compare every output to that. I repeat the same steps using the on board pink noise generator and see what results I get (right side of the screen). The bottom right hand corner is showing that the phase of output 6 is unaligned with output 5. 5-6 is a stereo pair and that waveform should be the same. The other picture is just like an RTA, I can see the level of every frequency I need there, you can see the Turquoise one (5-6) has a massive drop around 8kHz which is the odd alignment I heard, the LF is still present which is what made me suspect a latency issue originally rather than a full phase flip. 9-10 also did this, colored in blue. The “Stereo Outputs” pictures really just show what I heard when I was testing some cable at the shop, it made me check if the pin out was correct on the cable and then gave me quite the run around trying to figure out what was going on.

I’m no wordsmith, but it appears there’s a filter that has its phase unaligned from the rest of the source, some weird stuff is going on that I wish I could explain but I myself am not there yet with smaart to really dig into that, I’ve got the basics.

What I take from this; if I was using this handy tool to time align a rig and a room, I may be getting skewed results and if I was in show and this happened that would make my day really bad. I found this in the shop, I’m super happy about that!

Cheers,
Jeremy Moffitt

[Giga]

Ok, thanks !

Question: do you take the RTA plots for the stereo sources with one mic measuring 2 speakers firing ? 1 Mic, 1 speaker for the mono sources ?

Did you also use the exact same setup when you measured the mains out ?

What I’m getting at is that a less thank optimal measuring environment could also influence the outcome of the test I imagine ?

Giga

[Anonymous]

Is this a matter occurring only when u use a stagebox ? I recently experienced a similar problem during a meeting. It left me clueless with a client asking where the delay between 2 speakers came from..
It would explain a lot. I was only using the qu16 console with 5 very carefully delayed groups.
The problem however started occurring after roughly 22 minutes….
Anybody got a suggestion; please tell.

[JMO]

The Mic did not move for any of the screen shots using the RTA, all 3 of the pics would be identical if it were a reflection or a sub-optimal room (mixes 5-6. 7-8. 9-10). The pictures of the RTA are not very useful, expect to illustrate what was missing from what I originally heard in 2 of the mixes. For the rest of the photo’s, thereon I actually just went directly into my Smaart interface to get the best reading possible, so no mic involved. This was the most sure way to avoid any skewed results, I was just being a dumb dumb in the morning.

Cheers,
Jeremy Moffitt

[JMO]

This issue was created by the pink noise generator on the console. Not sure how your phantom delays happened!

Sorry,
Jeremy Moffitt

[Giga]

Thanks for your explaination Jeremy ! If I have some time left this christmas I will try to replicate this with my Qu-SB as far as that’s possible with my very basic setup and see what happens.

Giga

[Giga]

Sooooo, went and experimented a bit with this. Activated the noisegenerator on monomixes 1 through 4 amd stereomixes 5/6 through 9/10 and mains. Connected the headphonesoutput directly to 2 inputs on my interface, panned them hard left and right, set up a stereotrack and inserted a phasemeter and a spectrummeter. All eq’s etc. disabled.

I’m not phasemeter savvy enough to be able to interpret the results but there are definitely huge differences in the view the phasemeter gives when combining f.i. left mains with mix 1 vs. looking at main L against main R. Thank goodness at least the mains are fine…

Then watched the RTA; overall fine except in mix 5-6 and 9-10 which have a huge dip at 8 kHz (white and pink noise). That also shows when using “sine” for a signalsource.
An average signalstrength of -48dB shows a dip to -79dB in white noise, this is in L+R mode. L-R mode shows 8kHz as loudest with a dip at 16 kHz. Looking at either L or R seperately gives a perfect graph

I have zero clue as to what is happening here but, at least in my case, the honourable Mr. Moffitt is on to something.

I’m just happy my or any bandmembers ears never noticed anything 😉

Giga

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