Digital pop noise, during performance?

[Robin300]

Hi there

 

I was hoping to trawl thorugh the depths of wisdom here in the Blue room with my query.

 

A quick explanation on my circumstances and then into the problem.

 

I'm touring a show that loads in at 7am and begins at 1pm and is in and out for the day only. This means there is little time to properly flash out any issues or even run some numbers before I operate the show.

 

The show consists of a small group of performers on in ear monitors and Trantec radios with DPA head mics. I am operating from an LS9-32 and the music is played back from laptops, through a DI, using QLab software.

 

The problem I'm getting is one I have'nt experienced before and I don't have a number 2 soundie to help chase it. So finding the source during performance is difficult. It is an intermittent 'digital type' knocking or popping noise coming through the PA.

 

Sometimes it is occasional sometimes it is constant.

 

It will occur when there is no music playing, so it is not recorded on the tracks and it is highly intermittent. I think it relates to one actor and their radio beltpack. I seemed to have identified that much.

 

It isn't the usual or rather obvious, radio static or broken connector burst, instead it is a perfect bleep or knock sound.

 

Has anyone experienced similar problems? Do you need more information perhaps? I'm stumped.

 

Cheers

 

Rob.

[Mark M]

Are you playing MP3's? Ive had a similar thing randomly which seems to get worse when my laptop gets hotter.

[boswell]

One of the performers(or you) leaving their mobile switched on and near the beltpack or sound equipment? Switch to silent is not enough

[Robin300]

Are you playing MP3's? Ive had a similar thing randomly which seems to get worse when my laptop gets hotter.

 

Laptop getting hot is something I thought about, though I've swapped to my back up lappie which doesn't get as hot and it isn't doing it. Also it seems to be related to the performers movment.

 

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One of the performers(or you) leaving their mobile switched on and near the beltpack or sound equipment? Switch to silent is not enough

 

Its Possible the actor is leaving their mobile on and in their pocket, I'll chase that through. Do you have an experience of a similar problem?

[GreatBigHippy]

Are you running the laptop outputs through an audio interface?

Digital glitch can occur on buffer overrun so it there is a little too much going on with the laptop it could be that. Just a thought.

The other stupid thing is to make sure nothing at all else is running on that laptop inc. antivirus etc.

But a bleep sound sounds like digital glitch to me.

 

EDIT - SP

[Robin300]

No, Straight out of the headphone jack, not good I know, but its how I inherited the show. Tha lappies aren't running anything else, thats for sure, though the buffer overrun, is a possibility. The bleeps tend to happen by the end of the performance, well into an hour of running Q's.

[boswell]

One of the performers(or you) leaving their mobile switched on and near the beltpack or sound equipment? Switch to silent is not enough

 

Its Possible the actor is leaving their mobile on and in their pocket, I'll chase that through. Do you have an experience of a similar problem?

 

Yes, if the mobile is switch to silent or vibrate instead of OFF, it still transmits at intervals to the local base station and this can get picked up on any kit that is close to it

[cedd]

Really easy way to prove it's not the laptop would be to split its' output and run to a recorder of some sort, cd, DAT, HDD, another laptop,whatever! If you hear this pop then have a glance up, look at the record clock on the recorder for a rough time, then go back to it at a later date and have a listen.

 

If it's proven not to be the laptop, start splitting some other groups of channels off, perhaps group the radio mics into 2 auxes to start with, and record them individually on the left and right channels. You can then narrow it down to a smaller group. Keep going until you find the offending channel.

 

If your recorder doesn't see anything, then it's the main outputs of the desk, or something post-channel strip.

 

Might take a few attempts, or you may strike it lucky, but it could be the only way of pinning it down.

[Kevin Ross]

You could try turning on peak hold on the LS9. The pop will most likely be louder than the music so it will show above the rest of the signals and be held identifying the offending channel.

[TomHoward]

You could try turning on peak hold on the LS9. The pop will most likely be louder than the music so it will show above the rest of the signals and be held identifying the offending channel.

I didn't realise the LS9 had a peak hold - that's really useful.

 

Mobile phone noise has a distinct sound - there's an example

.

[Solstace]

Some thoughts:

 

1) Is the laptop charging circuit switching into "charge" mode mid-performance?

2) Is the 3.5mm laptop jack plug or socket dirty, or faulty?

3) Are you running your radio microphones on frequencies known to be clear of intermodulation?

4) Is there another venue nearby that could be using radio mics in the same frequency band?

5) Are your mics getting sweaty?

[RGSD]

This sometimes happens if transmitters are placed near each other.... For example, if an actor is wearing two transmitters then they should be on either hip or on the small of the turns back and the other around their thigh. If you have IEM's then again the receiver pack should be as far away from any other packs as possible!

 

have a word with anyone backstage and find out if the packs are being placed together at any point.... maybe if you have pack swaps or if all the turns are huddled up together! It doesn't matter if they arn't live on the desk - it interferes with other packs that are live and there is your feed for the noise!

 

Obviously if there arn't any transmitters live through the system at the time of the noises then it isn't the above....

[Robin300]

This sometimes happens if transmitters are placed near each other.... For example, if an actor is wearing two transmitters then they should be on either hip or on the small of the turns back and the other around their thigh. If you have IEM's then again the receiver pack should be as far away from any other packs as possible!

 

have a word with anyone backstage and find out if the packs are being placed together at any point.... maybe if you have pack swaps or if all the turns are huddled up together! It doesn't matter if they arn't live on the desk - it interferes with other packs that are live and there is your feed for the noise!

 

Obviously if there arn't any transmitters live through the system at the time of the noises then it isn't the above....

 

To everyone on this post thank you tremendously for your thoughts. I've really considered them closely. To RGSD, One trantec reciever and one IE transmitter are, side by side on the back of the body. That is the same for everyone in the show. Interestingly though, It isn't a squelch sound as such, particularly a digital knock. Is this something you have heard? Like a perfect digital knock sound, not a burst of static or intermode, which I'm familiar with?

 

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Some thoughts:

 

1) Is the laptop charging circuit switching into "charge" mode mid-performance?

2) Is the 3.5mm laptop jack plug or socket dirty, or faulty?

3) Are you running your radio microphones on frequencies known to be clear of intermodulation?

4) Is there another venue nearby that could be using radio mics in the same frequency band?

5) Are your mics getting sweaty?

This is a late reply and thanks for your thoughts.

 

Items 2,3,4 and 5 can be discounted, because I've looked at those possibilities. Usually problems associated with what you've outlined are more squelchy / static burst interference. From intermode or reflections. I'm getting a clear digital knocking. Really something I've never heard before. Item 1. is something I'll invesitagte.

 

Cheers.

 

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You could try turning on peak hold on the LS9. The pop will most likely be louder than the music so it will show above the rest of the signals and be held identifying the offending channel.

Thanks Kevin. That's a good call, because I've been keeping my I on the Levels, hoping It'll happen as I'm watching. Didn't think about this option.

 

Cheers.

[TomHoward]

With a Macbook you need to click 'Keep CoreAudio Alive' in the Sound settings of QLab to stop the audio driver going to sleep and then getting that 'pop' when a cue starts again.

[iainhewitt]

Some thoughts:

 

1) Is the laptop charging circuit switching into "charge" mode mid-performance?

 

 

I once had a similar problem with bad signal noise that turned out to be caused by this. The headphone socket was being used, so we switched to an external audio interface and problem solved.

 

HTH

 

Iain