SOLVED: Audio problem - HELP!

Ahh, now I get it Greg. Pad output to allow the fader to come up; that's the signal/noise issue. Duhh. I don't know why I couldn't follow that point. The light is now on inside my brain.
 
Now you have to understand -- the levels on the mixer weren't set to accommodate the video recording. They were set for the purpose of the PA system, so that things could be heard by the congregation. I have no doubt that whoever set them didn't have a whole lot of knowledge about proper gain settings on the amplifier, and I admit that I don't either. But it sounds like I need the faders on the mixer to be up higher. Doing that is going to make the audio louder on the speakers, which doesn't need to happen.

So it sounds as though I need to turn the gain on the amplifier down a bit, so that I am able to turn the gain on the mixer levels up more in order to increase the signal-to-noise ratio, is that right? And then put in the attenuating cable to the camcorder to get the levels back down from line level to mic level.

Have I got that straight?
 
If the system was set up so that the PA system speaker levels were "nominal" when the mixer meter was reading very low, then the PA system levels aren't set properly.
It doesn't do the PA system OR the video recording any benefit to operate the mixer at levels that are too low for proper operation.
 
Richard Crowley said:
If the system was set up so that the PA system speaker levels were "nominal" when the mixer meter was reading very low, then the PA system levels aren't set properly.
It doesn't do the PA system OR the video recording any benefit to operate the mixer at levels that are too low for proper operation.
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I agree. So if the speaker output levels sound fine, but the faders on the mixer are low, that means either the output gain on the mixer (to the amp) is set too high or the amp's gain is set too high, or both -- am I right about that?
 
Richard Crowley said:
It means that the gain of the power amplifier that feeds the speakers is set too high.
That forces the mixer to operate "down in the mud" near the noise floor.
Gain Staging is one of the most important parts of configuring an audio system.
https://en.wikipedia.org/wiki/Audio_signal_flow
Click to expand...

That was helpful a bit, but it assumed I knew some terminology I didn't. This was also useful -- http://www.proacousticsusa.com/blog/2012/03/how-to-set-up-a-church-sound-system/
 
Here's another question....actually, two questions.

1. Which output from the mixer should I be using to go to the input on the Peavey 600C amplifier?

2. Which input on the amplifier should I be using to connect from the mixer? Currently I believe it's connected via 1/4" plug to the #2 Hi-Z input.

Again, this is the way all of this was connected up long ago by someone who isn't there anymore. I want to get it connected correctly.

While we're at it, I may as well ask #3.

3. Which output on the Peavey amp should I be connecting the church's speakers to?
 
1) It is customary to use the MAIN output to feed the FOH ("Front Of House") system.
"Front of House" refers to everything beyond the stage. So that does NOT include stage monitors, etc.
It most commonly refers to the main speaker system provided for the audience.

2) That isn't really a "proper" PA amplifier, but a power amp is a power amp.
There do not appear to be ANY suitable "line-level" inputs to that amplifier.
All the inputs are low-level microphone (low-impedance) or low-level instrument (high-impedance).
No wonder it is running at high gain, because that is all it has.
If there isn't some kind of line-level input, then you should probably either use another attenuator
(such as suggested for the video camera), or get a proper PA system power amplifier with line-level inputs.

3) There appear to be only a pair of 1/4 inch phone jacks on the back for speakers.
What other options even exist? None that I can see.
 
Richard Crowley said:
1) It is customary to use the MAIN output to feed the FOH ("Front Of House") system.
"Front of House" refers to everything beyond the stage. So that does NOT include stage monitors, etc.
It most commonly refers to the main speaker system provided for the audience.

2) That isn't really a "proper" PA amplifier, but a power amp is a power amp.
There do not appear to be ANY suitable "line-level" inputs to that amplifier.
All the inputs are low-level microphone (low-impedance) or low-level instrument (high-impedance).
No wonder it is running at high gain, because that is all it has.
If there isn't some kind of line-level input, then you should probably either use another attenuator
(such as suggested for the video camera), or get a proper PA system power amplifier with line-level inputs.

3) There appear to be only a pair of 1/4 inch phone jacks on the back for speakers.
What other options even exist? None that I can see.
Click to expand...

Excellent info! Thank you sir!

What would be a similar (in terms of power output) but better-suited amplifier that could be had for a reasonable cost?
 
Actually I looked at the manual (which pretty much sucks) and the jack on the far right labeled "power amp input" is a line level in. That is what your mixer should be feeding. It implies that there are "tape in jacks" (mentions that plugging in to the Aux In defeats them) but nowhere does it show or talk about the "tape in" jacks so?

For those following this thread this is a sort of one stop "PA" system that powers two speakers but is mono. It has a mic in and an instrument in and a few places where yu can patch to sections like the EQ.

The specifications go on for awhile but there is no diagram and to specks are listed for the "power amp input" So I have no idea if it's balanced or not. Off the bat I would guess that it's an unbalanced -10dB, because that is the kind of output one would be expecting with this kind of use.

So that would match the "tape out" jacks on the mixer. May also match the main outs, though those may be +4 which would be very hot to patch into a -10 input.

This sounds a bit like consumer hell. You have a bunch of things that were really not meant to be connected together so it's going to be a fight to get things to act as they should.

It's more $ but IF you can't turn off AGC on the cam corder you might want to get one of those Juce Link boxes that feeds it a inaudible signal to keep the AGC from working so you can set a gain and not have the camera filling the gaps with noise.

One more thought.

If the input on the camera is a mic in on a 1/8" jack, it is probably feeding "plug in" power to the cable and that may be part of the buz problem. I have had plug-in power cause problems when it got sent to outputs that are not prepared to have power pushed at them. THe isolating transformer would solve that by blocking the voltage.
 
Richard Crowley said:
So that does NOT include stage monitors, etc.
Click to expand...

Since you mentioned 'stage monitors'....

The guy who trained me -- and it's clear that he doesn't know much either -- keeps saying that he needs to get a tall ladder and disconnect a speaker that someone (I assume him) installed so that the choir could hear. (The choir sits behind the pulpit.) He says that ever since that speaker was installed, they've had to keep the output levels lower to avoid feedback. I assume it feeds back into the microphones that are suspended above the choir.

What I infer from that is that whoever installed it just wired that speaker in with all the other speakers, since that speaker can't be controlled independently from the others. (Hence the need for the tall ladder to disconnect it.)

That speaker, as far as I know, is the only speaker that is used as any kind of monitor -- it does allow the choir to hear themselves when they sing. There are no other monitor speakers set anywhere, only the main house speakers.

For whatever use that information is...
 
Noiz2 said:
Actually I looked at the manual (which pretty much sucks) and the jack on the far right labeled "power amp input" is a line level in. That is what your mixer should be feeding. It implies that there are "tape in jacks" (mentions that plugging in to the Aux In defeats them) but nowhere does it show or talk about the "tape in" jacks so?
Click to expand...

I do see that! Excellent point. I'll give that a try.


This sounds a bit like consumer hell. You have a bunch of things that were really not meant to be connected together so it's going to be a fight to get things to act as they should.
Click to expand...

You got that right.

It's more $ but IF you can't turn off AGC on the cam corder you might want to get one of those Juce Link boxes that feeds it a inaudible signal to keep the AGC from working so you can set a gain and not have the camera filling the gaps with noise.
Click to expand...

That might work, but for what one of those costs we could just buy the Canon HF R62 with manual audio control, which would eliminate the problem as well.

One more thought.

If the input on the camera is a mic in on a 1/8" jack, it is probably feeding "plug in" power to the cable and that may be part of the buz problem. I have had plug-in power cause problems when it got sent to outputs that are not prepared to have power pushed at them. THe isolating transformer would solve that by blocking the voltage.
Click to expand...

Definitely something to consider. Thanks Scott!
 
Speakers themselves would not create a ground loop, it's power amp certainly could though, be it an internal powered speaker cab or powered external from a external amp. It it's powered by the same amp as the other speakers, an L-pad (passive speaker level volume control) 'should have' been put in-line.
 
As technical director of a large chorus, I CRINGED at the thought of using the sound system for the choir "to hear themselves when they sing".
Are the acoustic properties of the choir area really so terrible that they can't hear themselves?
Using a single, overhead monitor to "foldback" the choir from hanging mics is a perfect recipe for FEEDBACK HELL, right there in your church!

At the very LEAST that choir monitor speaker should have its own amplifier and its own output from the mixer.
That would allow you to adjust what is going into that "montor" speaker and minimize feedback from the choir's own mics.
 
Richard Crowley said:
As technical director of a large chorus, I CRINGED at the thought of using the sound system for the choir "to hear themselves when they sing".
Are the acoustic properties of the choir area really so terrible that they can't hear themselves?
Using a single, overhead monitor to "foldback" the choir from hanging mics is a perfect recipe for FEEDBACK HELL, right there in your church!

At the very LEAST that choir monitor speaker should have its own amplifier and its own output from the mixer.
That would allow you to adjust what is going into that "montor" speaker and minimize feedback from the choir's own mics.
Click to expand...

I totally agree. My point was that this 'monitor' speaker for the choir is likely one reason they felt they needed to keep the gain low -- to prevent feedback. The thing is, they should have lowered the gain on the amplifier, not on the mixer. Right?

If I lower the gain on the amplifier, I can then raise the gain on the faders to achieve the same overall sound level on the speakers, correct? And in doing so, I will increase the separation between the signal and the mixer's noise floor, am I right? Which, in turn, means a better level to the camcorder, right? Then attenuating the signal to the camcorder from line level to mic level might make a big difference in the level of the hum.

Am I on the right track?
 
The problem of feedback from the hanging choir mics back into the choir monitor speakers is completely INDEPENDENT of the level issues.
The choir feedback problem is a matter of MIXING and SEPARATING the choir monitor mix from the FOH mix. It has nothing to do with gain staging.

That $50 isolation box (presumably transformers) is good for breaking ground loops.
But we haven't definitively established whether you actually have a ground loop problem.
The fact that the sound is reasonably good during the sermon (etc.) indicates that there probably is NOT a ground loop problem.
At least from what I have read in this discussion so far.

Furthermore, the $20 solution I suggested from Radio Shack would probably also work for the mixer -> camera feed.
Spend the other $30 on something more important.
 
Richard Crowley said:
The problem of feedback from the hanging choir mics back into the choir monitor speakers is completely INDEPENDENT of the level issues.
The choir feedback problem is a matter of MIXING and SEPARATING the choir monitor mix from the FOH mix. It has nothing to do with gain staging.
Click to expand...

But that speaker isn't on its own channel -- it is connected in with the main speakers, so it can't be mixed separately. There is no 'choir monitor mix'. And no practical way to set one up, as it would require taking that speaker out of its current connections, recabling it, running cable through the ceiling back to the mixer, and setting up a mixer channel for it. Now granted, that's what SHOULD happen if we really want a proper setup. But getting that done would be a monumental task. I don't see that happening anytime soon. The most I can see happening is the guy getting on the ladder and just disconnecting that one speaker.

What I'm saying is that this extra speaker is what forced them to reduce the gain levels in order to avoid feedback. And instead of reducing the level at the amplifier, they just pulled back on the faders on the mixer -- which, I assume, brought the signal level down closer to the floor noise level.

It seems our goal is to get the signal-to-noise ratio on the mixer to be higher, right?

Doing so means pushing the faders up higher than their current levels, right?

If we do that, it's going to make the sound coming through the speakers louder and probably going to cause feedback because of that one speaker, so to prevent that we need to reduce the gain on the amplifier. Right?

Doing all of that will give us the same sound levels in the sanctuary that we have now, but with the mixer faders pushed up higher, won't it?

If so, won't that increase the separation between the signal and the mixer's noise floor? And isn't that a desirable thing?

It doesn't change the fact that an attenuating cable is still needed. I get that. But won't it lower the mixer's floor noise relative to the signal strength?
 
Richard Crowley said:
The fact that the sound is reasonably good during the sermon (etc.) indicates that there probably is NOT a ground loop problem.
Click to expand...

I agree. Especially considering the hum is not heard at all in the speakers. It's not heard at all in the DVD recording, which gets its audio feed from the mixer. It's only heard -- ONLY heard -- in the audio on the camcorder. And even then, it's only really heard when the AGC boosts the signal up during quiet moments.

It seems logical to me that an attenuation cable may help with that problem. It may reduce the noise (hum) signal low enough that the camera's AGC will ignore it. At least, that's what I hope. The only way to know for sure is to buy one and try it.
 
Richard Crowley said:
As technical director of a large chorus, I CRINGED at the thought of using the sound system for the choir "to hear themselves when they sing".
Click to expand...

I probably misstated that. I don't think the speaker was put there so the choir could hear themselves sing -- I think it was put there so the choir could hear the preacher, since they sit behind him and he's speaking out and away from them. However, it has the same effect when they are singing as a monitor speaker, in that it's outputting right into the choir's own microphones, setting up the feedback problem. And because the level on that speaker can't be controlled separately, the level of ALL speakers has to be lowered in order to prevent the feedback.

Not a smart configuration.

Perhaps we could add a pad to that one speaker. Drop the level on it so we can raise the level on the house speakers. Have to consider that.
 
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