SOLVED: Audio problem - HELP!

David W. Richardson;1986578789...(Since the buzz continues even with all inputs unplugged from the mixer said:
Since everyone with experience seems to agree that the cause of choice is a ground loop I would check that out before replacing equipment. THe loop would appear to be between the mixer and the camera so I would stick a ground lifter on one and see if that fixes the problem. I had thought the the length of time that it took to build up had to do with it being a big loop but maybe it is the AGC making that happen so?

And as someone mentioned earlier you could also probably stop the hum with an isolation transformer. THey are sold as iso boxes or hum stoppers.

BTW is there a headphone jack on the mixer? If so to you hear the hum in the mixer when nothing is connected? If so then maybe it is a blown mixer?
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Noiz2 said:
Since everyone with experience seems to agree that the cause of choice is a ground loop I would check that out before replacing equipment. THe loop would appear to be between the mixer and the camera so I would stick a ground lifter on one and see if that fixes the problem. I had thought the the length of time that it took to build up had to do with it being a big loop but maybe it is the AGC making that happen so?

And as someone mentioned earlier you could also probably stop the hum with an isolation transformer. THey are sold as iso boxes or hum stoppers.

BTW is there a headphone jack on the mixer? If so to you hear the hum in the mixer when nothing is connected? If so then maybe it is a blown mixer?
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If it's a ground fault loop between the mixer and the camera, then it would pretty much have to be coming from the mixer, since the hum is still there even when the camera is run on battery with no AC connected to it -- right?

There is a headphone jack on the mixer, but I haven't had a plug adapter to adapt the 3.5mm plug on my headphones to the 1/4" jack on the board. I will do that, though.

I think you're right that the hum is low, but gradually magnified by the AGC on the camera. I sure wish that AGC could be turned off!
 
David W. Richardson said:
If it's a ground fault loop between the mixer and the camera, then it would pretty much have to be coming from the mixer, since the hum is still there even when the camera is run on battery with no AC connected to it -- right?
........!
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You've got us confused with descriptions and you refuse to draw a diagram. So who knows at this point.
Two of us suggested a hum eliminator. You aren't willing to spend $15 on that. But you are willing to spend money on a new amplifier and mixer on a hunch without first testing to see if that's what it is.

And to top it all off, your willing to risk wasting a good-hearted donation on a fix that may not work. How will that doner feel when you spend their money and it still buzzes? I really hope the mixer fix works or I wouldn't show up next Sunday.

Good luck, I'm out.
 
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Well we got into the cabinet yesterday and pulled out the amplifier and the power conditioner, along with a bunch of other crap that didn't need to be in there in the first place.

I thought I saw the problem -- a real 'a-HA!' moment. The power cable for the amplifier was plugged into the power conditioner, as it should be -- but they had attached one of those three prong-to-two prong ground adapters onto the cable before plugging it into the power conditioner. Completely unnecessary, since the conditioner had 3-prong plugs on it. I thought, "THAT must be it! The amplifier isn't grounded!"

No such luck. Removed the adapter and plugged the amp straight into the conditioner -- no effect on the buzz.

Powered off and unplugged AC to the amp, and disconnected the two mono cables that ran from the mixer to the amp. No effect on the buzz.

Unplugged the mixer from the conditioner, powered off and unplugged the conditioner from AC. No effect on the buzz.

It's looking more and more like the source of the buzz is the mixer. Even if there was some kind of line noise coming from the main power, the power conditioner should have eliminated it -- assuming that the power conditioner was working properly. If it wasn't, then a new conditioner or a ground loop isolator should, I think, take care of it.

Received the RF modulator, so now I can remove that old VCR from the system. New mixer should be in sometime between now and next Wednesday. I've already told the preacher that they need to replace that camcorder with one that has manual controls for the audio.

In the meantime, I'm going to connect my Zoom H1 to an output from the mixer and record sound to that. Then I'll just replace the camcorder's soundtrack with the one from the Zoom, and everything should sound great. That will do as a workaround for now.

[EDIT] It occurs to me that the one thing I didn't do was connect the mixer straight to AC power. As it is now, it is connected to a power strip, which is connected to the power conditioner. I suppose it's possible that the power strip is somehow causing the buzz. I will investigate that.
 
I realize this may just add to your confusion but ground loops are not caused by a lack of a ground but by too many grounds. The ideal grounding scenario looks a bit like an asterisk where all of the grounds come back to a single point and that point is what is literally grounded. AC power ground should be isolated from your audio ground so you kind of have two asterisks. But if those grounds cross connect or part of your asterisk loops back so you have a loop rather than a star, that is where the problems start. The loop acts like an antenna and the closest RF is your power so that is generally what you hear.
 
Noiz2 said:
I realize this may just add to your confusion but ground loops are not caused by a lack of a ground but by too many grounds. The ideal grounding scenario looks a bit like an asterisk where all of the grounds come back to a single point and that point is what is literally grounded. AC power ground should be isolated from your audio ground so you kind of have two asterisks. But if those grounds cross connect or part of your asterisk loops back so you have a loop rather than a star, that is where the problems start. The loop acts like an antenna and the closest RF is your power so that is generally what you hear.
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Good info! Thanks Scott. I'm learning!

The amp is plugged (power-wise) to the power conditioner. Everything else is plugged into power strips -- 2 of them chained together. One of the power strips is plugged into the power conditioner. So all power goes from a single outlet, through the power conditioner, then out to all the equipment.
 
Also, many folks have suggested a ground loop isolator. Where in the system would an isolator be inserted? The ones I've seen online mostly seem like they're intended to be placed inline along the audio path -- their connectors are typically RCA, coax, 3.5mm, etc. So I'm not sure where an isolator should be placed.

Since the buzz or hum is heard even with ALL inputs disconnected from the mixer, it seems like an isolator would go inline between the mixer and the camcorder. Would that be right?
 
David W. Richardson said:
Also, many folks have suggested a ground loop isolator.
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Yes. But first you should actually LISTEN to that audio feed that is going to your camcorder. Is it clean when you listen on headphones? If there is buzz there when it is NOT connected to the camera, then an isolation solution will do you no good. The problem is UPSTREAM and an isolator will not REMOVE it. An isolator will only PREVENT a problem caused by the interconnection of the two ends (the mixer/source and the camcorder/destination).

Where in the system would an isolator be inserted? The ones I've seen online mostly seem like they're intended to be placed inline along the audio path -- their connectors are typically RCA, coax, 3.5mm, etc. So I'm not sure where an isolator should be placed....it seems like an isolator would go inline between the mixer and the camcorder. Would that be right?
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Since the buzz or hum is heard even with ALL inputs disconnected from the mixer,
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That more strongly suggests that the buzz is created by the interconnection between the mixer output and the camcorder input.

From what I have read here, it is still NOT CLEAR to me...
1) Is the output of the mixer clean (absent buzz)? The main output going to the PA system? The output going to the camcorder?
This test must be done independently before you can determine whether an isolation transformer will be helpful.

2) You are probably feeding line-level out of the mixer. Does the camcorder support line-level audio input? Or does it have a mic-level input which dramatically exacerbates this problem?

To be honest, I haven't been closely following this discussion because the information coming back to us isn't precise or detailed enough to allow us to do a very good job of helping you.
 
I still hope you'll try the attenuating cable we discussed a few pages back between the mixer and camcorder. I'm fairly sure from looking up the equipment involved that you are feeding a line-level mixer output into a microphone-level input on the camera, which will raise the background noise substantially.

- Greg
 
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Richard Crowley said:
Yes. But first you should actually LISTEN to that audio feed that is going to your camcorder. Is it clean when you listen on headphones? If there is buzz there when it is NOT connected to the camera, then an isolation solution will do you no good. The problem is UPSTREAM and an isolator will not REMOVE it. An isolator will only PREVENT a problem caused by the interconnection of the two ends (the mixer/source and the camcorder/destination).

That more strongly suggests that the buzz is created by the interconnection between the mixer output and the camcorder input.

From what I have read here, it is still NOT CLEAR to me...
1) Is the output of the mixer clean (absent buzz)? The main output going to the PA system? The output going to the camcorder?
This test must be done independently before you can determine whether an isolation transformer will be helpful.

2) You are probably feeding line-level out of the mixer. Does the camcorder support line-level audio input? Or does it have a mic-level input which dramatically exacerbates this problem?

To be honest, I haven't been closely following this discussion because the information coming back to us isn't precise or detailed enough to allow us to do a very good job of helping you.
Click to expand...

Okay, the buzz isn't present on the PA speakers or on headphones connected to the mixer's headphone jack. In fact, with isolation headphones connected to the mixer and no one speaking into a mic or playing the piano, it's virtually dead silent, even if I run the output levels up to the max.

The thing is, when someone IS talking into either the pulpit mic or the wireless mic, or the choir is singing, etc., the audio on the camera is downright great. So I don't think it's a line-level overload or anything like that. It's only when there's silence that there's a problem.

Clearly the AGC on the camera is ramping up the volume on this hum during those silent moments. Unfortunately, on this particular camera there is no manual control of the audio, so the AGC is not able to be turned off.

I agree that it pretty much has to be in the connection between mixer and camera. But I've tried different cables, different cameras, and now we even have a brand new mixer, but still the same issue. I've even tried running the camera on battery rather than AC. Nothing seems to eliminate the hum.

This whole thing might be nothing more than the AGC on the camera boosting the standard noise floor of the mixer. If that's the case, then the church will need to buy a slightly better camera, like the Canon HF R62, which does have manual audio control. In the meantime, I plan to split the audio signal and run it into my Zoom H1, set to manual audio levels, so I can get a clean audio track to put in during editing. That's fine, as long as I'm the one doing the editing. But without me, they have no one to do it. In that event, they just upload the camcorder video files straight to the web, bad audio and all, which is what they did before I came along.

I'm sorry the information isn't precise or detailed enough -- I'm not an audio expert. I'm doing the best I can, but you have to remember that I don't have this system sitting in my living room where I can try things on the fly or even look at it to tell you what's connected where. I do appreciate the help.

A sound guy I know suggested I might get a cleaner signal to the camera if I used the XLR outputs, which would require a cable with 2 XLR (male) on one end and a single 3.5mm male stereo plug on the other. I can certainly get that cable, if it will make a difference.

Or I could get a cable to connect the RCA "Record Out" outputs to the camcorder -- reading the manual that came with the new mixer, this sounds like it might be the way to go. As it stands right now -- and this is the setup it had when I came into the picture -- the camera is connected to the 1/4" "Monitor Out (R)" jack through a splitter/adapter that is STEREO 1/4" male jack to 2 STEREO 3.5mm female plugs. I have wondered if a STEREO jack into a MONO plug might be an issue as well. Certainly seems like it should be.

I have no idea who put this whole mess together, but nobody there now seems to know anything about it, so they've never dared change anything. They think I'm a genius just because I knew how to move the cables over from the old mixer to the new one.
 
Greg Smith said:
Ii still hope you'll try the attenuating cable we discussed a few pages back between the mixer and camcorder. I'm fairly sure from looking up the equipment involved that you are feeding a line-level mixer output into a microphone-level input on the camera, which will raise the background noise substantially.

- Greg
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Well the only one I've found that might work is less than 1 foot long and costs $31.00. And it's a male connector on both ends, so I would have to get a female-to-female adapter to connect it to a cable long enough to reach the camera. But I'll keep looking.
 
The outputs on that mixer -- except for the "record out" -- are balanced line-level (+4 dBu) signals on a 3-conductor (TRS) phone jack. You can put a 2-conductor (TS) plug into those jacks to get an unbalanced, but still line-level, signal out.

Your camera's microphone input expects a signal at something like -40 or -50 dBv, approximately 100 times less voltage (or 10,000 times less power) than the mixer's output. Nowhere in reply #50 do you say explicitly that you tried an attenuator between the mixer and camera. I think this is necessary. By turning the mixer output way down and depending on the AGC and headroom of the camcorder's input stage, you can apparently get a recording without distortion when people are talking. That's good and actually rather remarkable under the circumstances. But when there's no significant signa; coming through the mixer, the AGC releases and pumps up the noise. If you reduced that by a factor of 100 using an attenuating cable, it would probably be nearly inaudible.

This is not mainly about balanced vs. unbalanced or 3-pin vs. 4-pin connectors. (BTW, the XLR and phone jacks on the output of your mixer carry identical types of signals -- only the physical arrangement of the pins is different.) It's about signal levels, which are way out of whack if you have a simple straight-through cable between the mixer's line output and the camera's microphone input.

That "record out" RCA jack is at -10 dBv, a common consumer audio equipment standard. It's less than the main line outputs by 15 dB or so, which is a step in the right direction, but still significantly higher than the camcorder was designed to accept. I think you'll do better to get an attenuating cable, ideally with a 2-conductor 1/4" plug on one end and the attenuating network located near a 3.5mm 2-conductor plug on the other. Places like Markertek may have this, or you could try the Radio Shack item and a couple of adapters that you identified earlier (although its 60 dB of attenuation may actually be a little too much).

Please try this and let us know what happens.

Did you ever get to change out the power strip that you talked about earlier? Since the problem started abruptly after a power "incident," I wonder if this is one of the strips with built in MOV surge suppressors, and one of them "blew" in the surge and is now passing through some high-voltage noise on your power lines. I suspect you would never have become aware of this if it weren't also for the level mismatch at the mixer output, though.

Really, really wish I could be there in person with my "bag of tricks" to help out. These things are so hard to diagnose remotely!

- Greg
 
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Greg Smith said:
The outputs on that mixer -- except for the "record out" -- are balanced line-level (+4 dBu) signals on a 3-conductor (TRS) phone jack. You can put a 2-conductor (TS) plug into those jacks to get an unbalanced, but still line-level, signal out.

Your camera's microphone input expects a signal at something like -40 or -50 dBv, approximately 100 times less voltage (or 10,000 times less power) than the mixer's output. Nowhere in reply #50 do you say explicitly that you tried an attenuator between the mixer and camera. I think this is necessary. By turning the mixer output way down and depending on the AGC and headroom of the camcorder's input stage, you can apparently get a recording without distortion when people are talking. That's good and actually rather remarkable under the circumstances. But when there's no significant signa; coming through the mixer, the AGC releases and pumps up the noise. If you reduced that by a factor of 100 using an attenuating cable, it would probably be nearly inaudible.

This is not mainly about balanced vs. unbalanced or 3-pin vs. 4-pin connectors. (BTW, the XLR and phone jacks on the output of your mixer carry identical types of signals -- only the physical arrangement of the pins is different.) It's about signal levels, which are way out of whack if you have a simple straight-through cable between the mixer's line output and the camera's microphone input.

That "record out" RCA jack is at -10 dBv, a common consumer audio equipment standard. It's less than the main line outputs by 15 dB or so, which is a step in the right direction, but still significantly higher than the camcorder was designed to accept. I think you'll do better to get an attenuating cable, ideally with a 2-conductor 1/4" plug on one end and the attenuating network located near a 3.5mm 2-conductor plug on the other. Places like Markertek may have this, or you could try the Radio Shack item and a couple of adapters that you identified earlier (although its 60 dB of attenuation may actually be a little too much).

Please try this and let us know what happens.

Did you ever get to change out the power strip that you talked about earlier? Since the problem started abruptly after a power "incident," I wonder if this is one of the strips with built in MOV surge suppressors, and one of them "blew" in the surge and is now passing through some high-voltage noise on your power lines. I suspect you would never have become aware of this if it weren't also for the level mismatch at the mixer output, though.

Really, really wish I could be there in person with my "bag of tricks" to help out. These things are so hard to diagnose remotely!

- Greg
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No, I haven't tried an attenuating cable. None are to be found locally, and what little I've found on Amazon or other places seemed pricey. The $31 cable says it has a -25dB L pad, and it's described as a "line to mic" cable. It's much too short to reach from the mixer to the camera, since it's only a few inches long. This is the attenuation cable I'm eyeing -- http://www.amazon.com/gp/product/B0...ue&ref_=ox_sc_act_title_1&smid=A2LXBKOLL3J3K6

There is also this cable -- same price, same length, but -33dB attenuation -- http://www.amazon.com/Sescom-LN2MIC...3846107&sr=8-29&keywords=3.5+attenuator+cable

Both of these cables seem to be intended to connect a Zoom audio recorder to a DSLR, so I'm not sure they're exactly right for this particular job. What do you think?

I've been trying to avoid adding any more adapters, gender-changers, etc. to the line than was absolutely necessary, since it seems each has the potential to introduce its own problems. But if it becomes necessary, then I will use what I have to use to get the job done.

Regarding the power strip, I did say that I unplugged everything from AC power except the mixer -- even unplugged the camcorder and ran it on battery -- and that I plugged the mixer directly into the AC outlet, so that bypassed both power strips and the power conditioner. The problem still occurred.

I understand what you're saying, and you may well be right. It seems a bit counter-intuitive to lower the signal level when it sounds so good at all times other than silence, but that could very well be the thing that needs to be done.

I do understand the difference between line level and mic level, and it certainly seems reasonable that line level from the mixer going into the camera's mic input would be a problem. It surprises me that ALL sound on the camera isn't distorted in that scenario. That being said, it's hard for me to fathom that, if the signal is loud enough for the camera to record good sound using an attenuation cable, that the base noise level wouldn't also be loud enough to trigger the AGC. But I'm not experience in this stuff, so that could be entirely possible. The only way I will know for sure is to spring for the cable and adapter and hope for the best.

What I would first like to do is connect the "Record Out" to the camcorder and see if that results in any significant lowering of the level of the hum. Since, as you say, that output is about 15dB less than what I'm currently using, I'd expect to see the noise level drop to some extent. If it does, then that would indicate to me that attenuation might be exactly the right way to go. It may also give me some idea of how much improvement I might anticipate from the -25dB drop that an attenuation cable would provide. Useful information.

If I ordered the cable right now, it wouldn't get here before Sunday morning's service. So I'm going to test with the "Record Out" first and see what happens. Meanwhile, I'm recording sound via the Zoom H1 for the time being, using its line level input. That will carry me for now.

I do appreciate all your help. Thank you!
 
Greg Smith said:
By turning the mixer output way down and depending on the AGC and headroom of the camcorder's input stage, you can apparently get a recording without distortion when people are talking.
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I actually don't have the mixer output 'way down'. The monitor level is set about midway, and the sliders for most all of the inputs are just under halfway. Maybe that is 'way down', I don't know. Seems about average to me. But as I've said, I'm a novice on these matters.
 
SUCCESS!

Well, a measure of success. By connecting the camera to the "Record Out" RCA jacks on the mixer, it appears the hum was reduced by about 40% or a little more. That's progress!

So Greg, it appears you may be right on target with the attenuation cable. The only question now is -- which one? -25dB, -33dB or -50dB? I don't want to go too far the other way and into a new problem. So what do you recommend?
 
Practically all mixer's outputs are XLR-M (male) (and/or 1/4" TRS jacks, and in many cases, RCA 'tape out' as well). Even with gender adapters, there's still no attenuation and would do nothing to help the 'suspected' ground-loop issue.

BTW, that particular cable would be used to take a stereo headphone or other unbalanced stereo output to two input channels on a mixer.
 
Rick R said:
Practically all mixer's outputs are XLR-M (male) (and/or 1/4" TRS jacks, and in many cases, RCA 'tape out' as well). Even with gender adapters, there's still no attenuation and would do nothing to help the 'suspected' ground-loop issue.

BTW, that particular cable would be used to take a stereo headphone or other unbalanced stereo output to two input channels on a mixer.
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The gender-changer wasn't intended to attenuate anything. It's simply needed to connect the 3.5mm male end of the attenuating cable to the 3.5mm male end of another cable in order to get a length long enough to reach from the camera to the mixer, since the attenuating cable is less than 1 foot long.

To be honest, I highly doubt it's a ground loop problem at this point. With EVERYTHING disconnected from AC power except the mixer, and EVERYTHING disconnected from the mixer except the cable to the camcorder, and the camcorder running on batter (not AC), the hum is still there. It seems to me that eliminates virtually any ground loop problem unless it's in the AC wiring of the church itself. If it is, there's very little I can do about that.

I see. Good point. The XLR ends of that cable are male and the outputs are also male. Gotcha. So perhaps this cable then -- http://www.amazon.com/Hosa-CYX-402F...lTBjQ-L&dpSrc=sims&preST=_AC_UL160_SR160,160_
 
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