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Signal flow for live band vocals

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Sean Kendall
Signal flow for live band vocals
on Mar 15, 2010 at 12:58:10 pm

Our church just purchased a couple more EQs and we now have enough to cover all of our vocal mics (eight total, I believe). The way we currently have the system set up is that all of our mics go straight into the mixer, then from the mixer we have four sub-outs going to four different EQs, then to amps for four monitors. We also have the Main Left and Right out, going into individual EQs, then to the amps for the Mains.

My question is, will it be best to run each of the vocal mics into an EQ first, then to the mixer and from the mixer, the outs going straight to the amps? I'm thinking this would be the best setup because right now if one mic has a specific frequency that is partial to feedback (let's just say 500Hz, for example), then when we notch that frequency out of the mains, it gets notched out for every mic.

Let me know if I'm right or wrong on this. Thanks.



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Bill Davis
Re: Signal flow for live band vocals
on Mar 16, 2010 at 1:01:10 am

Your idea isn't "wrong" it's just very dependent upon your particular board's signal flow.

Most consoles have EQ built into the channel strips. If this is NOT enough EQ to handle specific room problems, the traditional solution is to use Channel INSERTS to pull that strips signal out - route it through the EQ or feedback eliminator) and then back into the same channel strip for level control.

This keeps the processing isolated to that particular channel strip and doesn't affect any other board signal or channel.

On many boards, the channel insert is a single 1/4" jack that expects to see a stereo plug. Insert plugs are wired such that the insert plug carries BOTH a send circuit and a receive circuit. Properly wired, this single plug both feeds the channel strip signal OUT to a device like a stand alone EQ and also brings the same signal BACK into the strip via the same plug. So you need cables properly wired with a stereo 1/4" plug on one end - and TWO (typically) XLR connectors (wired in mono) on the other end - one of which is configured as the send and the other as the receive.

Do a web search on "gain structure" or "audio channel strip operation" and you should get good resources to help you understand the basic signal flow - then look up your own specific mixer to understand where and what patch points are available to allow you to access the channel strip signals at the point where injecting your EQ makes the most sense.

Good luck.





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Will Salley
Re: Signal flow for live band vocals
on Mar 16, 2010 at 3:15:11 am

There are a many ways to route signals to meet different needs, but there is also a very common practice that may simplify the rig. On the mains, put the best pair (if running stereo) of eq you have, the next best unit should go on the monitors. These do affect the mains and monitors globally - in this case - that's what you want.. Use these eqs to "balance the room", meaning that in your situation, you have a fixed installation, and your room dimensions don't change from night to night. Borrow, buy, or rent a spectrum analyzer or get someone with trained ears to come help. You will find that the room has nodes, or standing waves, that create the feedback and objectionable resonances in your mix. Find these frequencies and use the eq to diminish them. You can't get rid of them all together but you can get the bad stuff. Go all the way across from 20 -20k and make a note of each notch for future reference. Tune the monitor side first, then front-of-house (without the monitor up). After doing this correctly, If you have any feedback, it is because of simple feedback caused by too much gain. You can use the board eq to help with that, but the best way is to keep the mics out of the monitors. Having the room in balance (also called "tuned") will make the mix sound better as well as reduce feedback in a manageable way.

Placing an eq inline on each channel will certainly work, but it complicates things when they don't need to be. And here's a hint: When using an analog eq and if you don't have an analyzer, start with everything flat and boost the band to find the offending frequency, then cut it. Start at 1k and go up, then come back to 800 and go down. before long, you'll develop an ear for identifying the freqs. and it will become second nature.

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Jordan Wolf
Re: Signal flow for live band vocals
on Mar 16, 2010 at 8:04:22 am

First, if you can give us some specific gear models, that would help out a lot.

"The way we currently have the system set up is that all of our mics go straight into the mixer, then from the mixer we have four sub-outs going to four different EQs, then to amps for four monitors. We also have the Main Left and Right out, going into individual EQs, then to the amps for the Mains."

The way you're describing the "sub-outs", they sound like Auxiliary Sends. It may sound semantic, but some mixers ALSO have sub-outs (usually called Subgroup Outputs). Which one you are talking about will determine how correct the setup is.

"My question is, will it be best to run each of the vocal mics into an EQ first, then to the mixer and from the mixer, the outs going straight to the amps? I'm thinking this would be the best setup because right now if one mic has a specific frequency that is partial to feedback (let's just say 500Hz, for example), then when we notch that frequency out of the mains, it gets notched out for every mic."

Okay, well I see two separate situations here: (1) where the EQ is patched and (2) the desired function of the EQ.

For the first situation, you'll quickly find that the signal level will be extremely noisy and/or low, if present at all. This is because a microphone's electrical output is very small and needs to be boosted - the "gain" or "trim" knobs at the top of the mixer are in place to bring this low level up to a level that the rest of the components in the mixer (and further down the signal chain) can use.

Now for situation number 2: There are a number of ways to utilize the functions of an equalizer: feedback-fighting, tone-shaping, and system alignment. EQs used inline or inserted in the the monitor signal path will be primarily used to fight feedback. An EQ that is inline or inserted in the main speaker path will be primarily used for tone-shaping. System processors (usually located near the power amplifiers) use EQ to even out the frequency response of the system.

As for how you should use the EQs you have: if we assume they are graphic equalizers, then the resolution of each band may do more harm than good if inserted on any single channel. Most mixers/mixing consoles have EQs with knobs that (hopefully) allow control of at least one band of boost/cut and the center frequency desired. Some even allow for control over how wide/narrow the boost or cut is.

My recommendation is to "insert" the EQs over the Auxiliary Sends used for monitors and also "insert" them over the main outputs. Using them in this way, as compared to in-line (running a cable from the output of the mixer to the input of the EQ and then out to the amplifiers) will let you hear any changes you make on the EQs through headphones. That may help you learn frequencies and how cutting or boosting certain ones will affect a particular instrument/voice.

If you are interested in learning more about live sound reinforcement, I highly recommend checking out ProSoundWeb's Study Hall and forums, as it is focused much more on sound reinforcement. This forum is also a great place to ask questions but I have always felt it was more geared towards on-location audio recording and post-production.


Keep asking those questions.

Wolf
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