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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: John K. Harris on December 29, 2017, 11:08:07 pm

Title: Random Intermittent Noise in Sound System
Post by: John K. Harris on December 29, 2017, 11:08:07 pm
Hey All! This is my first post on here because I have a interesting question that I am searching an answer for. I work as the resident AV Tech at The Salvation Army Kroc Center in Hawaii. On the side I have my own sound/lighting business that I do.

My issue is with the PA system at the Kroc Center. Sometimes there is a unique intermittent noise that sounds like something is rewinding/giggling chipmunky type of sound coming out from the mains. I have not heard of this type of sound before. The noise occurs randomly and is not duplicatable. It has happened with vendor techs that we have here and mainly on external client's shows when we rent out our Worship and Performing Arts Center. To my knowledge it has not occurred on Sunday Services for church. I have been working at the Kroc Center for two years working almost every Sunday (just missed one Sunday for vacation) and I have never heard the noise.

Sometimes the noise has happened when the vendor techs only have a couple channels on and the rest of the channels have no signal. It has happened to at least a few of the vendor techs. I would like to say that it normally happens when I am not A1 but that would imply human error. We have brought in the company that installed the audio system to troubleshoot but the noise doesn't ever happen when they are here, because it is not a duplicatable sound.

I have included a schematic of our system.
Title: Re: Random Intermittent Noise in Sound System
Post by: Kevin Graf on December 30, 2017, 09:00:18 am
Find an amateur Ham radio operator, he will know another Ham that has the skill and equipment to search for a problem like this.
Title: Re: Random Intermittent Noise in Sound System
Post by: Keith Broughton on December 30, 2017, 09:30:24 am
This is one of the tougher trouble shooting problems you can have.
Start by keeping a record of time of date, time and duration of the noise to see if there is some kind of pattern. From this, you may be able to determine a "likely" time to trouble shoot.
usually, the idea is to eliminate components from the audio signal chain to get down to what device(s) are getting the noise.
I would start with disconnecting the inputs to the amps and work back, connecting one device, or cable run, at a time.
Also, check around the area for some antennas that might indicate a radio transmitter.


Title: Re: Random Intermittent Noise in Sound System
Post by: Mike Caldwell on December 30, 2017, 09:36:47 am
Find an amateur Ham radio operator, he will know another Ham that has the skill and equipment to search for a problem like this.

Maybe....maybe not, while maybe great in radio operation many will have no clue about the kind of system and equipment in John's system.


As for the noise you described, that is kind of how I would describe cell phone interference.
If that is the case check for open mic lines, bad mic cables, mic cables or wall plates with the shell tied to pin 1. Lot's of place for RF ingress in a system like you have, assuming it is an RF ingress problem.
What are your wireless mic frequencies.
Title: Re: Random Intermittent Noise in Sound System
Post by: Scott Helmke on December 30, 2017, 10:00:44 am
Divide and conquer. Looks like there are several places to start looking - output of video switcher, output of main mixer, output of speaker processor. Likely you could Y-cable various outputs into some kind of recording device, like a cheap MP3 recorder that can run for a day or two. If you get a report of noise, you can go back and check the recording. Don't hear the noise, move the recorder further downstream.

If at all possible train the users to listen more critically. Not just "noise in the speakers" but "noise in the left side", etc.
Title: Re: Random Intermittent Noise in Sound System
Post by: Ed Walters on December 30, 2017, 10:53:39 am

I have included a schematic of our system.

That wireless in the simple  system...what band? Is it off/muted when not in use?  Often, so-called simple systems are always live.  What you describe sounds like LTE. T-Mobile started activating 600 MHz in Hawaii last summer..... 

If that (or other) wireless are in the 600 bands, start by physically disconnecting that wireless and see if the problem stops. Disconnect it instead of turning it off so other helpful people don't turn it back on for you...

Ed Walters
Title: Re: Random Intermittent Noise in Sound System
Post by: Simon Lewis on December 30, 2017, 11:31:39 am
Also, check for things that might be affecting mains power or generating RF noise, such as arcing thermostat contacts...
Title: Re: Random Intermittent Noise in Sound System
Post by: Kevin Maxwell on December 30, 2017, 11:36:17 am
Hey All! This is my first post on here because I have a interesting question that I am searching an answer for. I work as the resident AV Tech at The Salvation Army Kroc Center in Hawaii. On the side I have my own sound/lighting business that I do.

My issue is with the PA system at the Kroc Center. Sometimes there is a unique intermittent noise that sounds like something is rewinding/giggling chipmunky type of sound coming out from the mains. I have not heard of this type of sound before. The noise occurs randomly and is not duplicatable. It has happened with vendor techs that we have here and mainly on external client's shows when we rent out our Worship and Performing Arts Center. To my knowledge it has not occurred on Sunday Services for church. I have been working at the Kroc Center for two years working almost every Sunday (just missed one Sunday for vacation) and I have never heard the noise.

Sometimes the noise has happened when the vendor techs only have a couple channels on and the rest of the channels have no signal. It has happened to at least a few of the vendor techs. I would like to say that it normally happens when I am not A1 but that would imply human error. We have brought in the company that installed the audio system to troubleshoot but the noise doesn't ever happen when they are here, because it is not a duplicatable sound.

I have included a schematic of our system.

https://www.youtube.com/watch?v=3OII3oeWruA
Listen at about 15 seconds in. Does it sound like that?
Title: Re: Random Intermittent Noise in Sound System
Post by: Chris Eddison on December 30, 2017, 11:59:05 am
Do you have access to a simple recording device that has a long run time and a line input? Something like a Zoom handheld recorder. If so then start inserting it at various points throughout the signal chain and just leave it running. Note the time you hit record and then get the operators to record the time the noise occurs. With a decent size card and the lowest recording quality it'll do you should only be hitting record once a day. If it's not happened that day, delete the file and start again tomorrow.

This will do 2 things - it'll give you a recording of the issue if it's there, which might be useful for analysis. More importantly though, if the sound occurs and the recorder doesn't pick it up then you know it's getting in to a system component sometime after that point.
Title: Re: Random Intermittent Noise in Sound System
Post by: Keith Broughton on December 30, 2017, 12:27:37 pm
Do you have access to a simple recording device that has a long run time and a line input? Something like a Zoom handheld recorder. If so then start inserting it at various points throughout the signal chain and just leave it running. Note the time you hit record and then get the operators to record the time the noise occurs. With a decent size card and the lowest recording quality it'll do you should only be hitting record once a day. If it's not happened that day, delete the file and start again tomorrow.

This will do 2 things - it'll give you a recording of the issue if it's there, which might be useful for analysis. More importantly though, if the sound occurs and the recorder doesn't pick it up then you know it's getting in to a system component sometime after that point.
Good concept!
Title: Re: Random Intermittent Noise in Sound System
Post by: Frank Koenig on December 30, 2017, 12:32:25 pm
Do you have access to a simple recording device that has a long run time and a line input? Something like a Zoom handheld recorder. If so then start inserting it at various points throughout the signal chain and just leave it running. Note the time you hit record and then get the operators to record the time the noise occurs. With a decent size card and the lowest recording quality it'll do you should only be hitting record once a day. If it's not happened that day, delete the file and start again tomorrow.

This will do 2 things - it'll give you a recording of the issue if it's there, which might be useful for analysis. More importantly though, if the sound occurs and the recorder doesn't pick it up then you know it's getting in to a system component sometime after that point.

This, exactly. And you can use an audio editor, such as Audacity, to scan quickly through the recordings to look for noise events. Beats sitting there listening for hours. Good luck. -F
Title: Re: Random Intermittent Noise in Sound System
Post by: Tim McCulloch on December 30, 2017, 01:39:58 pm
Maybe....maybe not, while maybe great in radio operation many will have no clue about the kind of system and equipment in John's system.


As for the noise you described, that is kind of how I would describe cell phone interference.
If that is the case check for open mic lines, bad mic cables, mic cables or wall plates with the shell tied to pin 1. Lot's of place for RF ingress in a system like you have, assuming it is an RF ingress problem.
What are your wireless mic frequencies.

The old "GSM" interference noise... that was my thought, too.

Question for the OP - does this noise happen with the system on but with nobody near microphones or the console?  If not, I'm guessing GSM "polling".  The control channel will use maximum RF to see what tower(s) respond, analyze the RF signal strength and data integrity for each tower and then connect to one of them.  The proximity of a GSM cell phone (T-Mobile, ATT, Cricket, others that use ATT/TMobile towers) to microphones, poorly shielded mic cables or even sitting next to the console is usually the culprit.
Title: Re: Random Intermittent Noise in Sound System
Post by: Dave Pluke on December 30, 2017, 01:46:29 pm
That wireless in the simple  system...what band? Is it off/muted when not in use?

I've had Sennheiser receivers make noise when the transmitter was out of range and the receiver was searching for it.  Have learned to turn those units off when not in use.

Dave
Title: Re: Random Intermittent Noise in Sound System
Post by: Art Welter on December 30, 2017, 02:14:43 pm
To my knowledge it has not occurred on Sunday Services for church. I have been working at the Kroc Center for two years working almost every Sunday (just missed one Sunday for vacation) and I have never heard the noise.
John,

Was the Record Out cord terminated when the noise occurred?

That cord looks like it could be an accident waiting to happen that you have missed out on for two years.

Art
Title: Re: Random Intermittent Noise in Sound System
Post by: Keith Finch on December 30, 2017, 06:02:17 pm
The Description "rewinding/giggling chipmunky type of sound " is similar to a Video Conferencing audio problem I recently encountered. In the Audio DSP the Echo Cancellation had been router incorrectly. This allowed the Far End audio to break through during near end transmission low level times. It could be that the designer used a template from another job to speed things up on the Nexia DSP.
Title: Re: Random Intermittent Noise in Sound System
Post by: John K. Harris on January 05, 2018, 11:39:59 pm
https://www.youtube.com/watch?v=3OII3oeWruA
Listen at about 15 seconds in. Does it sound like that?

Hey Kevin, thanks for this but unfortunately it does not sound like this. I know what the GSM interference sounds like and it is definitely not that. But thank you for your effort.
Title: Re: Random Intermittent Noise in Sound System
Post by: John K. Harris on January 05, 2018, 11:45:15 pm
John,

Was the Record Out cord terminated when the noise occurred?

That cord looks like it could be an accident waiting to happen that you have missed out on for two years.

Art

Hey Art, thank you for reminding me that I have to update my system schematic. Unfortunately that is not in the system anymore. Originally it was used as audio output from the EAW processor then going to the input for our old camera. Since we got a new camera that has XLR inputs I have then switched the cables to XLR cables and removed that 3.5mm cable from the system.
Title: Re: Random Intermittent Noise in Sound System
Post by: John K. Harris on January 06, 2018, 12:21:48 am
That wireless in the simple  system...what band? Is it off/muted when not in use?  Often, so-called simple systems are always live.  What you describe sounds like LTE. T-Mobile started activating 600 MHz in Hawaii last summer..... 

If that (or other) wireless are in the 600 bands, start by physically disconnecting that wireless and see if the problem stops. Disconnect it instead of turning it off so other helpful people don't turn it back on for you...

Ed Walters

Hi Ed!

Unfortunately the wireless system is in the 600MHz range. But I can definitely say that is another problem of it's own especially with lab pack dropouts.

But back to the first problem when these rentals occur there is only like a few wireless channels that are on during these events. At max maybe like four channels for most events, though some events have used of like 16 wireless channels but never had that "giggling sound". Almost every Sunday we use more than 8 wireless channels for our church services(we have two), but I have never heard it during church services.

On a side note to everyone, we used to have a Yamaha LS9-32 with a Whirlwind Digital Snake here and that sound occurred when we had that board too. Now we have the Presonus RM32/64 with a Presonus CS18ai and still have that sound.

As for the times of when that sound happens is entirely random, there have been some events that took place in the evening and that noise has happened, then other events throughout the day and the noise happens.
There has been events that were here all day and into the night but that sound/noise did not occur.

But I think adding a recorder to the system might help and that is a great idea, so thank you for that suggestion.

Also looking into the Nexia DSP might be another option, though to be honest I am not certified to work with the Nexia software. I could learn and figure it out pretty quickly but I wouldn't want to accidentally do something without knowing how to troubleshoot it. I guess I could say this about the Crestron system as well, as that I am not certified to use the Crestron software.
Title: Re: Random Intermittent Noise in Sound System
Post by: Mike Caldwell on January 06, 2018, 11:26:35 am

Also looking into the Nexia DSP might be another option, though to be honest I am not certified to work with the Nexia software. I could learn and figure it out pretty quickly but I wouldn't want to accidentally do something without knowing how to troubleshoot it. I guess I could say this about the Crestron system as well, as that I am not certified to use the Crestron software.

Actually looking into the Nexia DSP to watch the input and output metering coule be helpfull in narrowing down were the noise is coming from, watching for a spike in the levels and noting where it showed up at.

Assuming of course the installer connected the metering function blocks to the inputs and outputs!!

You can download the software from the Bi-Amp website.

To get into the Nexia you would need to know it's IP address and if needed any passwords. Getting to the live view layout from there is not to tough, in live view you can open up processing blocks and change levels, EQ, Ect.....so be careful!! Look for the input output blocks generally on the left and right of the layout page, you should see bunch of lines "wires" going to a meter block as well as lines connecting to the various processing blocks.

As for the Crestron unit you pretty much need to be a certified Crestron programmer to have the software to really get into their equipment.
Title: Re: Random Intermittent Noise in Sound System
Post by: Magnus Högkvist on January 06, 2018, 11:36:20 am
On a side note to everyone, we used to have a Yamaha LS9-32 with a Whirlwind Digital Snake here and that sound occurred when we had that board too. Now we have the Presonus RM32/64 with a Presonus CS18ai and still have that sound.

Do You still use the same Whirlwind cable?
Title: Re: Random Intermittent Noise in Sound System
Post by: Todd Friemuth on January 07, 2018, 04:57:36 am
Maybe I've missed this detail as I just quickly looked over your system diagram, but I didn't notice what type of PA system you are dealing with. You don't happen to have any older Crown I-Tech's in use do you?
Title: Re: Random Intermittent Noise in Sound System
Post by: John K. Harris on January 07, 2018, 03:07:49 pm
Do You still use the same Whirlwind cable?

No, the Whirlwind digital snake got replaced by a Presonus RM32ai, the ethernet cable was the only thing that remained.


Maybe I've missed this detail as I just quickly looked over your system diagram, but I didn't notice what type of PA system you are dealing with. You don't happen to have any older Crown I-Tech's in use do you?

We have 4 QSC RMX-1850HD for the monitor wedges. For the mains we use EAW NTL720s for the mains and EAW NTS250s for subs.

So definitely no Crown I-Techs.

Actually looking into the Nexia DSP to watch the input and output metering coule be helpfull in narrowing down were the noise is coming from, watching for a spike in the levels and noting where it showed up at.

Assuming of course the installer connected the metering function blocks to the inputs and outputs!!

You can download the software from the Bi-Amp website.

To get into the Nexia you would need to know it's IP address and if needed any passwords. Getting to the live view layout from there is not to tough, in live view you can open up processing blocks and change levels, EQ, Ect.....so be careful!! Look for the input output blocks generally on the left and right of the layout page, you should see bunch of lines "wires" going to a meter block as well as lines connecting to the various processing blocks.

As for the Crestron unit you pretty much need to be a certified Crestron programmer to have the software to really get into their equipment.


Thank you for the guidance on the Nexia. The only thing is I don't think I have the password to access it though. I may have to contact the installer for it.
Title: Re: Random Intermittent Noise in Sound System
Post by: Magnus Högkvist on January 09, 2018, 01:03:25 pm
No, the Whirlwind digital snake got replaced by a Presonus RM32ai, the ethernet cable was the only thing that remained.

Yes, that was what I was trying to ask. So the cable from FOH to the stage is the same in the new setup as in the old, which also had the same noise?
Title: Re: Random Intermittent Noise in Sound System
Post by: John K. Harris on February 13, 2018, 10:11:01 pm
Actually looking into the Nexia DSP to watch the input and output metering coule be helpfull in narrowing down were the noise is coming from, watching for a spike in the levels and noting where it showed up at.

Assuming of course the installer connected the metering function blocks to the inputs and outputs!!

You can download the software from the Bi-Amp website.

To get into the Nexia you would need to know it's IP address and if needed any passwords. Getting to the live view layout from there is not to tough, in live view you can open up processing blocks and change levels, EQ, Ect.....so be careful!! Look for the input output blocks generally on the left and right of the layout page, you should see bunch of lines "wires" going to a meter block as well as lines connecting to the various processing blocks.

As for the Crestron unit you pretty much need to be a certified Crestron programmer to have the software to really get into their equipment.

So Mike, I actually got trained to use Audio/Nexia now, but just been to busy with other things to reply to this thread until now. I can upload a snapshot of the Nexia in the system into this post.

(https://lbq5ra-dm2305.files.1drv.com/y4m3mcgfc1rerWmBLodVzMZ6pI-NELhKLO6lzuwjPEkaAURUg3cFxPFYlj4ZV78xiueIWipOZ0vO0KoDAfrrCguv6p_2tNy6Abgxx9U1enWZ-ETnuXma9v1-qqIjjPePodmLXQf5S5jZxk4LFJHMFz6_rsCCrcKPuNELgbItl2BHfiYy5NWY_DAZxAh50IYxg3wwlLxlPMG5CPCSvAeeZmLNw?width=1366&height=768&cropmode=none)
Title: Re: Random Intermittent Noise in Sound System
Post by: Mike Caldwell on February 14, 2018, 08:34:48 pm
So Mike, I actually got trained to use Audio/Nexia now, but just been to busy with other things to reply to this thread until now. I can upload a snapshot of the Nexia in the system into this post.

(https://lbq5ra-dm2305.files.1drv.com/y4m3mcgfc1rerWmBLodVzMZ6pI-NELhKLO6lzuwjPEkaAURUg3cFxPFYlj4ZV78xiueIWipOZ0vO0KoDAfrrCguv6p_2tNy6Abgxx9U1enWZ-ETnuXma9v1-qqIjjPePodmLXQf5S5jZxk4LFJHMFz6_rsCCrcKPuNELgbItl2BHfiYy5NWY_DAZxAh50IYxg3wwlLxlPMG5CPCSvAeeZmLNw?width=1366&height=768&cropmode=none)

Most likely if you scroll that screen up you will find the block of input meters, watch the meters and if you see one of meters show a level spike at the same time you hear the noise then check that connected input source.
If any of those inputs have an open room mic on it you may see two level meter spikes, one from the source it self and the other from the mic picking up the noise. The direct source should be the higher one.
Of course the noise maybe coming from the output of the DSP or even further downstream in that case the input metering would not show it.

For the input meters to be active you need to be in the online live mode.
If the meters are not below the layout block click on the peak meter block.