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Author Topic: Issues with distortion on QLX-D1 when house is full  (Read 1440 times)

Zachary Sherman

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #10 on: March 19, 2019, 11:50:09 pm »

Eric: Our E6's don't have colored bands. It looks like they are just rubber bands that can slide off, so it's possible that's what happened to ours (they've likely been in service over 15 years with numerous operators, so anything could have happened). That said, as I mentioned, our elements have been used for many shows, including seven others I worked on sound for, and we've never had this issue with distortion, so I would hesitate to say this is the main issue.

Kevin:
- I like the tape idea! It would definitely be nice if we could hide the face tape, since for us, a piece of tape on the face is vital to the mic staying on well. We have the actors put on makeup first so it doesn't get on their mics, which makes it more difficult for the tape to stick, but it's better than ruining our mics by slathering them in makeup!
- Unfortunately, as for spare cables, we already have a pretty low budget, so usually if a mic breaks during a show, I just give it to the director to have it replaced for the next show run. This show run is over, so I won't be able to test more with multiple actors until probably June.
- Our transmitters can only be padded down on the receivers (QLXD1) and they are down far enough that they rarely, if ever, peak on the receivers.
- We do have an antenna distribution system which is rack mounted with the receivers in a portable (albeit really heavy) unit. Since it's a black box theater, there isn't space to put the receivers in the pit and I like to be able to see them during the show, especially when having problems like this distortion issue. But, like I mentioned, we've done many other shows with the receivers in this position and we've never had an issue.

TL;DR: I don't think I've found the culprit yet. I'm certain our mic elements aren't the issue, and the receivers are seeming less and less likely to be the problem. If anyone has a different suggestion, I would really appreciate it.

Thanks everyone for your help so far!
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Jason Glass

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #11 on: March 20, 2019, 12:17:38 am »

 

- Our transmitters can only be padded down on the receivers (QLXD1)...

Make sure that the QLXD1 "mic offset" setting is 0 and hasn't been mistakenly boosted.

The vast majority of gain structure related audio distortion with decent quality wireless is the result of overloading the transmitter audio input.  Receiver output gain is rarely the root cause.

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Russell Ault

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #12 on: March 20, 2019, 03:09:50 am »

Make sure that the QLXD1 "mic offset" setting is 0 and hasn't been mistakenly boosted.

The vast majority of gain structure related audio distortion with decent quality wireless is the result of overloading the transmitter audio input.  Receiver output gain is rarely the root cause.

While I'm not positive about the mic offset (although I get the impression it's just a digital trim), my understanding (from a Shure rep) was that QLXD and ULXD use a two-stage fixed-gain preamp on the TX, so the RX is basically the only place to set "gain" (which at that point is really just digital-to-analogue output headroom, or floating-point-to-integer conversion headroom in the case of Dante output).

That's why I was asking if the TxOL indicators ever turn on, because that indicates that the low-gain stage of the TX preamp is being over-driven, which as I understand it can happen even if the meters look good (and is impossible to solve without adding a physical inline pad).

In the case of the OP, I'm going to guess that the problem is that your E6s are indeed high-sens. The old ULX1 beltpacks had a pad switch and, according to specs, they should have been able to take an input signal of at least 16 dBV with the pad in. Unlike the successor ULXD1, the QLXD1 doesn't have a pad switch, and it maxes out at only 8.5 dBV, which might be a significant enough difference to explain your problem. Unfortunately if that's the case, it means the mics will probably have to be replaced with a low-sens version, unless someone feels like creatively building an inline pad into the TA4 connectors on those mics (pads are fairly simple circuits; pads that pass full bias voltage I'm guessing are not so much...)

-Russ
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Kevin Maxwell

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #13 on: March 20, 2019, 10:42:15 am »

Eric: Our E6's don't have colored bands. It looks like they are just rubber bands that can slide off, so it's possible that's what happened to ours (they've likely been in service over 15 years with numerous operators, so anything could have happened). That said, as I mentioned, our elements have been used for many shows, including seven others I worked on sound for, and we've never had this issue with distortion, so I would hesitate to say this is the main issue.

Kevin:
- I like the tape idea! It would definitely be nice if we could hide the face tape, since for us, a piece of tape on the face is vital to the mic staying on well. We have the actors put on makeup first so it doesn't get on their mics, which makes it more difficult for the tape to stick, but it's better than ruining our mics by slathering them in makeup!
- Unfortunately, as for spare cables, we already have a pretty low budget, so usually if a mic breaks during a show, I just give it to the director to have it replaced for the next show run. This show run is over, so I won't be able to test more with multiple actors until probably June.
- Our transmitters can only be padded down on the receivers (QLXD1) and they are down far enough that they rarely, if ever, peak on the receivers.
- We do have an antenna distribution system which is rack mounted with the receivers in a portable (albeit really heavy) unit. Since it's a black box theater, there isn't space to put the receivers in the pit and I like to be able to see them during the show, especially when having problems like this distortion issue. But, like I mentioned, we've done many other shows with the receivers in this position and we've never had an issue.

TL;DR: I don't think I've found the culprit yet. I'm certain our mic elements aren't the issue, and the receivers are seeming less and less likely to be the problem. If anyone has a different suggestion, I would really appreciate it.

Thanks everyone for your help so far!

To the tape and makeup issue Ė we put one piece of tape on the mic boom as close to the ear as we can and then sometimes we put one on the back of the ear. Then usually on the people with long hair we either Bobbie pin the cable to the back bottom center of the neck or use a wig clip to anchor the cable on actors with short hair we tape the cable at the back of the neck in a way that creates a strain relief. The strain on the cable is what usually causes the mic failures. Is becomes sort of an S shape for the strain relief. Regarding the makeup and tape sticking Ė we have the actors come to the micing crew ahead of them putting on their makeup and we put a piece of tape on their face where the tape will be when they get the mic tapes to them. Then the actors put on their makeup, they then come to the micing crew which are trained students, the tape is then taken off and you have a clean spot to tape the mic to them. Then you use the concealer makeup stick to blend the tape to their makeup.

BTW if properly bent an E6 will stay on someone without needing any tape or not much tape. I can bend one to stay on me without any tape (Countryman has videos to show how to do it) it might be a little tighter then is really comfortable for most people. But having said that I have never been able to make that work on another person. It may be that I know how to handle and bend an E6 without breaking it and I know how it feels on me but I donít know how it feels on them. And I donít trust another person to bend the E6, I have seen then break them.

You need to find a way to test whether the mic is distorting into the transmitters or not. You will probably never see the clipping anywhere on any of your meters, because if this is what is happening it is happening in the transmitter itself before the packs preamp. I would suggest you setup a speaker and put a tone thru it. You can find tone generator app for most smart phones. Ideally have this in another room then you are in and run a cable to the mixer from the receiver. This will be loud and annoying. Now put one of the mics about a foot in front of the speaker so it picks up this tone. I am suggesting a tone (especially if you can sweep the tone) because you will hear it and notice distortion easier than if you are playing music. This speaker will have to be under your control to change the volume. You will want to gradually increase the volume and it will be very loud during this test. It will reach a point where it will distort. If it reaches that point sooner than any of your metering shows clipping then the mic transmitter combination is the problem.

Where do you physically put the antennas? I would put them on mic stands out from under the audience seating. How are you seeing the receivers if they are under the seating? Where are you mixing from? Considering everything you are saying I would put the receivers next to the mix position. I hope you arenít mixing from under the seating. I always prefer to get the receivers (always with antenna distro) near the stage but this room sounds like it is small enough that you should be able to get away with them near the mixer and put the antennas up over the heads of the audience, mic stands should work. How long are the coax cables from the antennas to the receivers? What antennas are you using and are you using an In-line antenna amplifier? If you are what is it set to?
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Ike Zimbel

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #14 on: March 20, 2019, 10:51:32 am »

How long are the coax cables from the antennas to the receivers? What antennas are you using and are you using an In-line antenna amplifier? If you are what is it set to?
This is a good line of inquiry. I don't know if the QLX-D1 has an RF overload light or not, but I have (once) heard audio distortion that was caused by severe RF overload, and in that case it was from a UHF-R UR-2 Tx that was too close to a Shure paddle antenna that was in the +10dB gain position.
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Russell Ault

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #15 on: March 21, 2019, 01:43:07 am »

This is a good line of inquiry. I don't know if the QLX-D1 has an RF overload light or not, but I have (once) heard audio distortion that was caused by severe RF overload, and in that case it was from a UHF-R UR-2 Tx that was too close to a Shure paddle antenna that was in the +10dB gain position.

QLXD does have an RF OL indicator on the LCD. That being said, my impression was that the error correction in digital wireless is an all-or-nothing affair, so overloading the receiver might cause the audio to drop, but you shouldn't be able to do anything in the RF realm that will cause AF distortion beyond cutting in and out. Am I missing something?

-Russ
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Mark Rombouts

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #16 on: March 21, 2019, 04:18:19 am »

QLXD1 does not have an input pad, like ULXD1. That could be the problem.

If it overloads the input. You will get an error message on the receiver, so you should be able to duplicate that problem without a show. Just turn a system on and yell loud in to the E6 a short distance.
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Kevin Maxwell

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #17 on: March 21, 2019, 09:34:50 am »

QLXD1 does not have an input pad, like ULXD1. That could be the problem.

If it overloads the input. You will get an error message on the receiver, so you should be able to duplicate that problem without a show. Just turn a system on and yell loud in to the E6 a short distance.

You would think that but many times it is hard to tell when you are distorting if it is just on the edge of distortion with your own voice. And I have yelled into a mic and I can't get it to distort and then an excited singers get up on stage before a full audience and they are clipping the inputs. And it was fine during rehearsals. That is why I suggested the troubleshooting method above.
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Mark Rombouts

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #18 on: March 22, 2019, 02:50:28 pm »

You would think that but many times it is hard to tell when you are distorting if it is just on the edge of distortion with your own voice. And I have yelled into a mic and I can't get it to distort and then an excited singers get up on stage before a full audience and they are clipping the inputs. And it was fine during rehearsals. That is why I suggested the troubleshooting method above.

You don't have to hear it. If the input of the beltpack is clipping it will show on the display of the receiver, you can see it there.
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Eric Snodgrass

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #19 on: March 25, 2019, 12:28:54 am »

Eric: Our E6's don't have colored bands. It looks like they are just rubber bands that can slide off, so it's possible that's what happened to ours (they've likely been in service over 15 years with numerous operators, so anything could have happened). That said, as I mentioned, our elements have been used for many shows, including seven others I worked on sound for, and we've never had this issue with distortion, so I would hesitate to say this is the main issue.

I'm still voting for this being the issue, especially if these mics are not blue-band mics and they are over 15 years old.  Makeup, hairspray, food and water will probably have made their way into these mic capsules at some point over those 15+ years. 
Another thing - if the QLXD packs have Sensitivity settings then try adjusting them down.  I know on the Sennheiser ew100 packs that when I use over-the-ear mics I must adjust the Sensitivity down to around -39db in order for the mic signal to not overload the pack. 
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