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Author Topic: Testing the EQ of a FOH mixer  (Read 3191 times)

mark ahlenius

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Testing the EQ of a FOH mixer
« on: May 08, 2012, 07:03:45 am »

Hi,

this process that I am thinking about may seem a bit complex, but please stick with me for a minute.

We have a Midas Verona for FOH.  On one of the wireless channels (Shure UHR with a beta 58 head), we have been experiencing a very hollow sound.  That was my first suspicion, as it sounds different than the others in that set.  We've listened (others, not me) at the Shure receiver and it sounds fine there, but soloing on the channel strip, its hollow.  Right now my suspicion is on the Midas channel and would like to prove otherwise.  Listening to it on the board, doesn't necessarily tell me what frequency and perhaps EQ control the problem may be in.

Simply bypassing the EQ is the quickest test, but to prove that the EQ section is working properly - as well as A/B'ing by swapping that channel to another on the board.  But to test out the EQ for a channel strip - here's what I was thinking.

I take a CD I have of pink noise and route it to the mic input (direct box in reverse) of that channel strip and  I have an audio frequency spectrum analyzer on my laptop.   I can first route the pink noise directly to the laptop through the direct box and see how it sounds without going through the Midas - that would be my reference.   Then connect the laptop audio input to an output of the Midas which that channel is routed to, and then flatten the channel EQ for that channel and view the results.   

That should allow me to view colorization of the audio by the channel and also see exactly how each control effects the results, and of course compare it to other channels.

I know this is quite complex, but am just trying to see what may be going on here.  WHen you are testing this by yourself, it seems impossible to get that hollow sound you hear during worship practice or on Sunday morning - so am looking for ways to better diagnose this by myself.

ideas?

thx

'mark
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g'bye, Dick Rees

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Re: Testing the EQ of a FOH mixer
« Reply #1 on: May 08, 2012, 08:28:06 am »

Swap it to another channel.  Plug in one of the "non-hollow" sounding mics into the suspect channel.  What happens?

Before you go trying to test the gear you have to localize the problem.  If the problem follows the wireless rig, it's the rig. If the problem stays with the channel, it's the channel.

Another possibility is to simply flip the polarity switch on the channel and see if that fixes it. 
« Last Edit: May 08, 2012, 08:59:22 am by dick rees »
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Karl Winkler

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Re: Testing the EQ of a FOH mixer
« Reply #2 on: May 08, 2012, 11:24:25 am »

Swap it to another channel.  Plug in one of the "non-hollow" sounding mics into the suspect channel.  What happens?

Before you go trying to test the gear you have to localize the problem.  If the problem follows the wireless rig, it's the rig. If the problem stays with the channel, it's the channel.

Another possibility is to simply flip the polarity switch on the channel and see if that fixes it.

What he said.
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mark ahlenius

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Re: Testing the EQ of a FOH mixer
« Reply #3 on: May 08, 2012, 12:41:04 pm »

Swap it to another channel.  Plug in one of the "non-hollow" sounding mics into the suspect channel.  What happens?

Before you go trying to test the gear you have to localize the problem.  If the problem follows the wireless rig, it's the rig. If the problem stays with the channel, it's the channel.

Another possibility is to simply flip the polarity switch on the channel and see if that fixes it.

Yep thanks.

I did ask them to try this, but not sure they did on Sunday.

Will def try another channel and the phase button too before going down this other path.  I'm just thinking ahead.  When I had swapped the wireless units in the booth, a week before, they both sounded about the same with no hollowness. 

Best

'mark
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TJ (Tom) Cornish

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Re: Testing the EQ of a FOH mixer
« Reply #4 on: May 08, 2012, 01:17:32 pm »

Hollowness can also be cuased by comb filtering - multiple copies of the same signal at different times.  Check to see if there are any inserted devices on the channel in question - effects processors, etc. and turn off any aux sends.
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Lee Douglas

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Re: Testing the EQ of a FOH mixer
« Reply #5 on: May 08, 2012, 06:45:10 pm »

Hollowness can also be cuased by comb filtering - multiple copies of the same signal at different times.  Check to see if there are any inserted devices on the channel in question - effects processors, etc. and turn off any aux sends.

And make sure that it's the only thing soloed.
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Kent Thompson

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Re: Testing the EQ of a FOH mixer
« Reply #6 on: May 09, 2012, 03:50:01 pm »

Does that microphone go to a monitor that is near a hot microphone like a choir microphone? This exact thing happens when our pastor speaks with the choir microphone active.
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Re: Testing the EQ of a FOH mixer
« Reply #7 on: May 09, 2012, 04:01:58 pm »

Does that microphone go to a monitor that is near a hot microphone like a choir microphone? This exact thing happens when our pastor speaks with the choir microphone active.

This is what was hidden in my suggestion of flipping the polarity on the offending mic.  The nice thing about it is that if it does "fix" the problem it can be un-done and re-applied as needed.  When I'm doing anything with multiple lavs/headsets I keep one hand free for flipping things as needed when mic positions change.
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Kent Thompson

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Re: Testing the EQ of a FOH mixer
« Reply #8 on: May 10, 2012, 01:13:13 pm »

This is what was hidden in my suggestion of flipping the polarity on the offending mic.  The nice thing about it is that if it does "fix" the problem it can be un-done and re-applied as needed.  When I'm doing anything with multiple lavs/headsets I keep one hand free for flipping things as needed when mic positions change.

Pfft! Don't hide stuff!!! I might never find it LOL.
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