Low level from alt out

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This topic contains 21 replies, has 5 voices, and was last updated by Profile photo of volounteer volounteer 1 year, 5 months ago.

Viewing 15 posts - 1 through 15 (of 22 total)
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  • #89932
    Profile photo of idealtrucks
    idealtrucks
    Participant

    Our church just upgraded from an old analog board to a qu32. I record and stream our services. I have mix 7-8 sent to alt out. On my computer, the level is much much lower than it was from the analog board. I have the alt out knob maxed out, and mix 7-8 master is set to 0db. Same results sending lr to alt out. Why is the level so low? In OBS, I have a 6db gain filter applied to the audio.

    #89933
    Profile photo of volounteer
    volounteer
    Participant

    @idealtrucks

    Our church did the same thing. We get plenty of signal on any output.
    With one of them we actually could use a lot less , as our video camera only has a mike in no line level input.

    have you raised the preamp gain using the screen control?
    There may be another knob to do it too but the screen is easier.

    You should be able to get plenty of signal to match the old board.

    Do a select on your mix with the blue button and go to processing screen via that button and see what the gain is set at.
    Touch the amount then rotate the knob to adjust for more.

    #89941
    Profile photo of KeithJ A&H
    KeithJ A&H
    Moderator

    Hi @idealtrucks,

    As volounteer says, you should be able to match the level of the previous board.
    Some things to check:
    The connection – the Alt outputs are on balanced TRS jacks and so the optimum connection would be to a balanced input. If you are using say, a 3.5mm line input on the computer though, ensure that the cabling is correct.
    The level of Mix 7-8 – What level is it peaking at when you check the meters or use PAFL? Are you using this as a pre or post fade mix? Do you have any processing (e.g. compression) that’s reducing the level?

    If you are still having issues, please contact us using support.allen-heath.com with more details of the setup, and we’ll figure it out with you 🙂

    Cheers,
    Keith.

    #89944
    Profile photo of idealtrucks
    idealtrucks
    Participant

    Volunteer, I’ll check on the gain for the mix. I didn’t know that the mix as a whole had a gain.

    For my connection, I have adapters to take the TRS jacks to RCA, and going to my video mixer. The video mixer then goes to the computer through and HDMI capture card. It’s the exact same connection that I had before, except the analog board had RCA connections so I had to add the adapters. There’s also a low buzz in the signal I’m getting at the computer now. Not sure if it’s the adapters though.

    Mix 7-8 is not peaking very high, but I’ll check Wednesday service and get an exact level. It’s set to a post fade mix, with no process on the mix as a whole. The speaking mics do have compression turned on, but the sound out of the FOH speakers is great. The old board had compression on those channels as well. The music does not have any processing other other than EQ.

    #89945
    Profile photo of Mike C
    Mike C
    Participant

    I had posted to here earlier today but it disappeared!!

    As Keith mentioned and as I did the first time and now that you responded your connections may be the issue.
    – When you mention TRS jack to RCA is that a single 1/4 inch TRS plug that breaks out into to RCA connectors? If so that in it self could be a big part of the issue.
    The balanced line signal on the 1/4 inch TRS output jack is being phase cancelled at the
    stereo input on you mixer. Your old board that had RCA outputs that were a true left right stereo output.

    You will need to take both of the ALT outputs and run them separately into the stereo inputs on the mixer. To take care of the buzz you should use transformer isolation between the mixer and the audio inputs on the video system.
    The transformer isolation can be dual purpose, convert from balanced to unbalanced and provide isolation to take care of the buzz.

    Back to your mix 7 8 settings…..

    Fist I assume you have assigned mix 7 8 directly to the ALT OUT.

    There is no “preamp” as such for a mix just the overall level setting with the mix master level control. That said ultimately the input channel preamp gain is where it all starts.
    As Keith said signal processing applied to a mix can change the overall level of a mix.

    Do you have good levels from the input channels for the main mix on the PA system?
    When you PFL the channels one at a time where is the average level on the meter?

    When you select mix 7 8 with the blue select button all the faders more or less become the aux knobs you were used to on your analog board.
    What was the main LR master level fader is now the overall mix level fader, where do you have it set at?

    To use a mix to feed a recording you want to set that mix to be post fade and post EQ so that the mix to recording will track what you are doing for the main system mix.

    You will also want to set all the channel mix sends to the same level with maybe bumping up the mix sends on the spoken word inputs.
    For an easy starting point set them all at unity with the spoken word mic inputs bumped up as they normally are lower on a recording.

    #89947
    Profile photo of KeithJ A&H
    KeithJ A&H
    Moderator

    Hi @idealtrucks,

    The nominal output level of the Alt Out is +4dBu and maxes out at +22dBu, you might check this against the specs of your previous board just in case there is a huge difference.

    There is some testing you could do without any extra equipment though.
    The simplest is to use the SigGen, set to output at 0dB on Mix 7-8, this would show if the level difference is somewhere between Mix 7-8 and the capture card (rather than the inputs going to Mix 7-8).

    You could also loop your RCA cable back to the Qu, and use the two adaptors on either end of, say, the white/left side of the cable.
    This will allow you to connect the Alt Out back to a line input of the Qu.
    Ensure this input is not routed to Mix 7-8! Then put some known signal into an input that IS routed to Mix 7-8 and set levels as you normally would.
    Looking at the signal level coming back into the ‘test’ input will show if there’s an issue with the cable or output of the Qu and take the video mixer out of the equation.

    Not entirely necessary, but I’d recommend getting familiar with the block diagram here:
    https://www.allen-heath.com/media/Qu-Mixer-Reference-Guide-AP9372_10.pdf#page=8&zoom=130,-252,496
    as this always helps when troubleshooting and just understanding the signal path.

    Cheers,
    Keith.

    #89953
    Profile photo of idealtrucks
    idealtrucks
    Participant

    Thank you for that information. So according to the block diagram, there is no gain on the mix
    I will try those tests and post back my results.

    #89954
    Profile photo of Mike C
    Mike C
    Participant

    Post up a picture or two of the cabling between the mixer and the video system.

    #89955
    Profile photo of idealtrucks
    idealtrucks
    Participant

    Mike C, I just saw your earlier reply and tried to edit my post, but I don’t think it took.
    What I have right now for the adapters is: https://www.sweetwater.com/store/detail/GPR101–hosa-gpr-101-rca-female-to-1-4-inch-ts-male-adapters-2-pack These are plugged into the two alt out jacks, and an RCA cable goes to the video mixer, with a splitter to a CD recorder. All the same as the other board except those two parts from sweetwater.
    And yes, I have mix 7-8 post fade, post eq. All faders, including master are at 0, with the exception of a few adjustment to certain channels.

    I’m not sure what you mean by a transformer. Would something like this be better? https://www.amazon.com/RCA-XLR-Audio-Cord-Professional/dp/B000V1RLI2 Sorry, I’m no professional sound man 😉

    #89958
    Profile photo of volounteer
    volounteer
    Participant

    @idealtrucks

    The BLOCK diagram on p89 of the Qu32 manual will be better than the SIGNAL FLOW diagram on page 8..
    Just what do you have feeding signal to alt out? [mix 7/8]
    Can you raise the gain on that input(s) to [ mix 7/8] at its channel strip?

    Following up on MikeC’s note: Could one of your inputs to the video be reversed polarity so they are tending to cancel?

    Or could your channel inputs be phase reversed cancelling before they get to mix 7/8?

    Following up on KeithJ A&H, I seriously doubt that the old board you had could put out more signal than the Qu does.

    What is the input to the video mixer connector wise? You said the old board had RCA.
    Could you skip the RCA adapters and use a cable that matches the Qu and the video mixer?

    Could you use the two track out instead of the alt out?

    We use a matrix to feed our video. Could you try that output to see if it gives you enough gain?

    Can you raise the gain in the video mixer or computer?

    This really sounds like the adapters are causing the problem or you are not putting enough signal into the mix 7/8 feeding the alt out.

    #89960
    Profile photo of Mike C
    Mike C
    Participant

    The 1/4 inch to RCA plugin adapters are correct in that they are giving you an unbalanced connection to the video system but they do not give you any ground and signal isolation between the sound system and the video system. The lack of isolation is the cause of the buzz and hum.

    Are the RCA inputs the only audio input available on your video system.

    Did you have the hum and buzz with your analog board?.

    Here are a few links to transformer isolation of various types.

    For this one it would be best to use 1/4inch TRS to XLR male adapter cables to connect it to the audio and take the RCA outputs to your video system.
    ART Dual Isolator

    This piece would connect inline with the RCA cables.
    RDL Hum Killer

    Like the ART unit only a more professional build.
    Radial Pro ISO

    #89961
    Profile photo of idealtrucks
    idealtrucks
    Participant

    Thank you for the isolators.

    I did not have any buzz on the old analog board It was RCA out, and my video mixer is RCA in.

    As far as the level goes, since alt out is balanced, and I’m plugging in a mono adapter, would that be cutting the volume since it’s basically cutting out a conductor? The old board would have been an unbalanced out I assume.

    #89962
    Profile photo of garyh
    garyh
    Participant

    A balanced input will reverse the phase of the signal on one wire, summing the now in-phase signals on the two wires, thus increasing the level but canceling the noise.

    #89963
    Profile photo of Mike C
    Mike C
    Participant

    Gary’s correct only in this case an unbalanced line drive should have plenty of level to drive the RCA -10 inputs on the video system.

    A balanced line audio has the signal carried on two lines with one of them having the phase inverted 180 degrees. ON and XLR connector pin 2 is positive and pin negative, pin 1 ground, on a 1/4 inch TRS the tip is positive and the ring is negative, the sleeve is ground.

    Don’t confuse negative and ground, in a balanced line the ground is not the audio return path like it is in an unbalanced audio path.
    The noise cancellation takes place at the input of the audio equipment, since the audio is carried on two lines that are out 180 degrees out of phase with each other any noise
    that is picked up along the way is picked up equally and of the same phase relationship on both of the lines in the cable. At the input of the equipment the negative phase audio line is inverted back to positive and summed together with the positive audio line giving you full level signal.

    In the summing process any noise that was picked up is cancelled out because the noise that was was same on both lines during the summing process is inverted 180 degrees on one line cancelling just the noise.

    Sometimes in a balanced audio connecting between equipment that has buzz or hum just disconnection the ground at one end will take care of that, the audio ground not the power ground.

    #89964
    Profile photo of Mike C
    Mike C
    Participant

    As for not having any buzz with the analog board, did anything else change at the time
    of the digital board change over.

    Is there any way the audio from the video system is getting looped back into the board?

    If by chance you have an output from the video system connected to the mixer and that input is turned up on mix 7 8 that could be causing a direct audio loop cancelling out
    a lot of the signal level.

    Having an input channel polarity flipped would not cause this overall issue, though if you have two input channels coming from the same source, having the polarity flipped on one of them MAY cause an issue just with that source in the way of cancellation. Sometimes with two inputs from the same source with will need to flip the polarity on one of the inputs, the classic is micing a snare drum, one mic on top, one on the bottom. the bottom mic will get the polarity flipped to match the top mics polarity output.

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