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Author Topic: Issues with distortion on QLX-D1 when house is full  (Read 1150 times)

Zachary Sherman

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Issues with distortion on QLX-D1 when house is full
« on: March 12, 2019, 12:39:07 pm »

Hi! This is my first post on the forum, but I've been working on sound for a few years. I'm a senior in high school, and I run sound for our theater productions. We've just finished our run of Seussical, but we had a weird issue I'd like some help resolving.

We now use fourteen Shure QLX-D1 mic packs with mostly Countryman E6 elements. We used to have the ULX system, but we switched because of the T-mobile 600mhz situation. The new mics were installed over the summer, and the frequencies were presumably set by someone who knew what they were doing. We have a Yamaha IM8-32 analog console, which is plenty for our needs.

Before each show, I mic'ed everyone up according to the Countryman manual as I've done for plenty of shows with no issues. We completed mic checks, including having each actor sing their loudest song with the (already too loud and not even mic'ed) live band and had no issues. Afterward, we had a couple groups of actors who usually sing together do their songs, and again had no issues. Last, I turned on all the mics for the actors' vocal warm-ups, and of course, still no issues. I could push them as far as I wanted and, although too loud, they sounded fine.

The house was then opened, and the audience piled in. As soon as each show started, it was distortion galore! It couldn't have sounded any worse. I immediately checked the receivers, and found that they were not peaking. I then checked the board, and no channels were peaking either. Finally, I checked the master monitor, and found no peaking.

A couple more important pieces of info about the setup:
1. Our receivers are placed under about five rows of platform seating. It's a black box theater, so there isn't a better spot.
2. We've never had issues with distortion before when the receivers were placed here. I've done seven other shows in the same theater, including one with these mics.
3. The theater holds about 200-300 people. It's none too big: from all the way upstage to the back of house wall is probably fifty feet.
4. During the show, each receiver indicates full RF signal.
5. The problem usually seems worse when many mics are on (even when their faders are set to ~-20dB and neither the receivers nor the main mix are peaking), but some mics distort by themselves.

Any ideas why this might have been going on? It seemed very weird to me and was certainly incredibly frustrating!
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Russell Ault

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #1 on: March 12, 2019, 01:19:32 pm »

Hi! This is my first post on the forum [...]

Hi! The rules of this forum require that your display Name (it's in your Account Settings) be your real first and last name. No one will answer your question until you've changed it, and this thread will probably be locked in the mean time.

-Russ
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Andrien (No Last Name)

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #2 on: March 17, 2019, 12:07:32 pm »

Do you have networking in place? You can try to use Shure Workbench and see the RF signal on the fly to monitor each QLX-D during shows.
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Russell Ault

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #3 on: March 17, 2019, 01:53:40 pm »

The house was then opened, and the audience piled in. As soon as each show started, it was distortion galore! It couldn't have sounded any worse. I immediately checked the receivers, and found that they were not peaking. I then checked the board, and no channels were peaking either. Finally, I checked the master monitor, and found no peaking.

A couple more important pieces of info about the setup:
1. Our receivers are placed under about five rows of platform seating. It's a black box theater, so there isn't a better spot.
2. We've never had issues with distortion before when the receivers were placed here. I've done seven other shows in the same theater, including one with these mics.
3. The theater holds about 200-300 people. It's none too big: from all the way upstage to the back of house wall is probably fifty feet.
4. During the show, each receiver indicates full RF signal.
5. The problem usually seems worse when many mics are on (even when their faders are set to ~-20dB and neither the receivers nor the main mix are peaking), but some mics distort by themselves.

Any ideas why this might have been going on? It seemed very weird to me and was certainly incredibly frustrating!

Do you have a recording of the distortion you were hearing? Do the TxOL indicators on the receivers ever turn on?

To add to what Andrien said, Wireless Workbench also creates a log of warnings (like audio peaking), so being able to monitor the receivers in software can be very useful for troubleshooting these problems.

That being said, if the QLXD system says it's happy (which it sounds like it is from your description of the problem) I tend to believe it. QLXD packs are some of the easiest wireless to gainstage, and they do a pretty good job letting you know when something is wrong. Also, because of the error checking built in, digital wireless tends to be an all-or-nothing affair: it tends to drop out completely if the wireless signal is too garbled to receive.

If the wireless seems happy, and the console seems happy, is it possible that you're overdriving something further down the line, like PA processing or something like that? Things getting louder when the audience comes in is a pretty common occurrence (both because singers never sing as loud during soundcheck as they do during a show, and because the audience is absorbing a significant amount of sound energy that your PA now has to make up for). This might also explain why the problem seems worse the more mics you have on. Does the distortion show up if you listen to the output of your sound board on headphones?

-Russ
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Mike Caldwell

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #4 on: March 17, 2019, 05:37:26 pm »

Did PFL and listen to any of the individual mics to see what they sounded like?

Did any other wireless equipment get fired up at show time...that your were aware of other than the 200 cell phones that walked into the room?

After you recovered from the show did you test it again with the system at the same levels to see what you had then?

Ike Zimbel

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #5 on: March 17, 2019, 05:57:47 pm »

Hi! This is my first post on the forum, but I've been working on sound for a few years. I'm a senior in high school, and I run sound for our theater productions. We've just finished our run of Seussical, but we had a weird issue I'd like some help resolving.

We now use fourteen Shure QLX-D1 mic packs with mostly Countryman E6 elements. We used to have the ULX system, but we switched because of the T-mobile 600mhz situation. The new mics were installed over the summer, and the frequencies were presumably set by someone who knew what they were doing. We have a Yamaha IM8-32 analog console, which is plenty for our needs.

Before each show, I mic'ed everyone up according to the Countryman manual as I've done for plenty of shows with no issues. We completed mic checks, including having each actor sing their loudest song with the (already too loud and not even mic'ed) live band and had no issues. Afterward, we had a couple groups of actors who usually sing together do their songs, and again had no issues. Last, I turned on all the mics for the actors' vocal warm-ups, and of course, still no issues. I could push them as far as I wanted and, although too loud, they sounded fine.

The house was then opened, and the audience piled in. As soon as each show started, it was distortion galore! It couldn't have sounded any worse. I immediately checked the receivers, and found that they were not peaking. I then checked the board, and no channels were peaking either. Finally, I checked the master monitor, and found no peaking.

A couple more important pieces of info about the setup:
1. Our receivers are placed under about five rows of platform seating. It's a black box theater, so there isn't a better spot.
2. We've never had issues with distortion before when the receivers were placed here. I've done seven other shows in the same theater, including one with these mics.
3. The theater holds about 200-300 people. It's none too big: from all the way upstage to the back of house wall is probably fifty feet.
4. During the show, each receiver indicates full RF signal.
5. The problem usually seems worse when many mics are on (even when their faders are set to ~-20dB and neither the receivers nor the main mix are peaking), but some mics distort by themselves.

Any ideas why this might have been going on? It seemed very weird to me and was certainly incredibly frustrating!
Hi Zachary, welcome to the forum, and good on you for posting such an informative and detailed request.
I don't have a lot to offer here except that Russ' theory that you're overloading something downstream from the mixer seems like a good one to pursue. What happens when you play pre-recorded tracks through the system?
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Eric Snodgrass

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #6 on: March 17, 2019, 07:59:13 pm »

To add to this speculation -
Your singers might be overloading the E6 mics.  That wouldn't show up on the meters of either the pack or the receiver.
Mic placement for the E6 mics is critical.  As was mentioned in a previous post in this thread, singers (especially amateur singers) almost never sing out full during sound check.  Mic check might have gone well, but then they put on their costumes and mic placement can change.  The E6 mics are typically long, physically.  Getting the mic element past the cheek and into the front of the mouth area is really easy and not at all desirable with the E6 as a strong singer will tend to overload the mic element.  It's one of the reasons Countryman makes a shorter version of the earset mic, the E2.  Even adults can have head diameters too small for the E6 to sit behind the mouth (to avoid overloading and breath noises).  I have a corporate gig that I do occasionally where the host must wear an E2 because the E6 is too long for her. 
The E6 also comes in different sensitivities.  No colored band on the mic means it's going to be best for general speaking.  A blue band on an E6 means that mic's output is attenuated - these are much better for loud speech and most singers.  A purple band has the most attenuation and are suited for the loudest vocalists. 
So, if you have E6 mics with no colored bands on powerful singers and the elements are too close to their mouths then they will overload and distort. 
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Zachary Sherman

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #7 on: March 17, 2019, 08:46:08 pm »

Thank you all so much for your help!

Adrien:
- We don't, although it's something I would love to do! I might ask our school's IT department if they've got a 16 (or more) port switch and a laptop I can borrow, since we've got 14 mics. Since I'm graduating this year and the students I was training haven't done sound stuff before this year, I'm not sure it's something I want to leave them with, but it certainly would be cool. It's kind of like how I would have loved to a digital board for this production to fix EQ and help mix using an iPad without the trainees having me over their shoulders. It would've been great, but it's definitely not something the new students will properly know how to use without taking advantage of it.

Russell:
- Unfortunately, I didn't record the distortion. During this show run since I was training new students to do sound, I wasn't able to record while (attempting to) fix problems and helping them mix.
- As for overdriving something later down the line, I doubt this is the case because we've had so many other shows where volume has been no issue. We usually can raise it farther than as high as is comfortable without any noticeable audio issues.
- I tried to monitor with headphones, but unfortunately all I had with me was a crappy pair of earbuds and an adapter, so the mix didn't sound right through that anyway. I believe I remember hearing the distortion through the headphone port, but unfortunately, I can't remember for certain.

Mike:
- As far as I know, we didn't start up any other wireless devices at the beginning of the show. All of lighting's lights were wired to my knowledge, and we have all wired ClearComs.
- My music teacher thought phones entering the room might have something to do with it, but I'm skeptical, since we've had so many other successful shows with phones in the room. Also, the phones should theoretically be transmitting and receiving at 2.4GHz (Wifi and 4G) whereas the mics are on the 500MHz band.

Ike:
- We didn't try pre-recorded stuff at loud volumes, but the sound effects and intermission music (which were played loud enough to be heard over the actors) sounded fine.

Eric:
- We were wondering about this as well. Before each show, while the house is filling up, the actors scream backstage as part of their "pre-show rituals." The director was wondering if the mics were being "blown out" during this. What do you think?
- I've been following the Countryman instructions for placing the mics. I've attached a picture of roughly how I mic up actors so you can verify whether or not I'm doing it right. As I mentioned, I've done this for many other successful shows, so I don't think it's the issue, but it's definitely good to think about. In the picture, the black line is the mic, and the yellow squares are medical tape that we use to ensure the mics stay on while actors act.

Again, I really appreciate everyone's help. Hopefully we can get this sorted out!
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Eric Snodgrass

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #8 on: March 17, 2019, 10:15:16 pm »

The mics aren't being "blown out", but they could easily be distorting.  Check your E6 mics and see if they have small, colored bands on them near the cable connection.  If they don't, then it is most likely that the singers are overdriving the mic elements because the mics are too sensitive for the level produced by the singers.
Here is a link to a .pdf about the E6.  In it is an explanation and picture of the different color bands.

After you have positioned the mic on someone, have them smile.  If the mic is sticking in front of the corner of their mouth then it will definitely be more susceptible to sybilance and plosives (popping from wind generated by the mouth, typically on consonants such as P or B).  Also, taping the mic to the cheek where you are doing it puts the mic too tight to the mouth.  I recommend putting the tape back near the ear (avoiding any little hairs).  This will allow for you to pull the mic away from the mouth a bit, helping somewhat with plosives and sybilance.  It also gets an unsightly piece of tape off of their cheek and hides the tape better.   
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Kevin Maxwell

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #9 on: March 18, 2019, 02:18:46 pm »

Listen to what everyone is saying about the E6 mics and bout the actors singing a lot louder when there is an audience present. I donít know if your wireless transmitters can be padded down enough to fix this problem. Did you check to see if there is a band (blue?) on the E6. If they arenít one of the reduced gain version of the E6 whoever sold you this stuff doesnít know what they are doing. If this was purchased new and this is the first show you have done with these E6 mics the school needs to get in touch with the supplier and tell them they had better take these back and get you the right mics.

Also while we are on the subject of tape we use 3M Transpore tape and then use a concealer makeup stick to take the shine off of the tape and make it blend with the actors makeup. DO NOT use the type of concealer that sprays on a foam pad it will dissolve the glue in the tape, I think the liquid type is also bad. Be careful with the mic cable, if there is any stress on it (too tight) it may break internally. Be sure to have spare cables on hand.   

Do you have any more performances or is the show over? Do you have an antenna distribution system or are you just using the antennas on the back of the receivers? We always put the receivers in the pit or backstage with the antennas up high with a clear shot at the stage.
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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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Kevin Maxwell

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #20 on: March 25, 2019, 11:14:15 am »

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.

Not always. It depends on where the metering is. The mic could be too sensitive for the input stage and if the trim is set low it may not show on the meter but it will be over driving the input stage.

Have you ever given a video camera operator a line level signal out of you mixer only to have them set the camera to accept mic level and they turn the volume way down on the camera and their metering never shows a problem but the signal is distorted. Same results with a mic that is too sensitive for the input stage of the transmitter.
« Last Edit: March 25, 2019, 11:17:40 am by Kevin Maxwell »
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Mark Rombouts

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #21 on: March 25, 2019, 03:20:35 pm »

Not always. It depends on where the metering is. The mic could be too sensitive for the input stage and if the trim is set low it may not show on the meter but it will be over driving the input stage.

Have you ever given a video camera operator a line level signal out of you mixer only to have them set the camera to accept mic level and they turn the volume way down on the camera and their metering never shows a problem but the signal is distorted. Same results with a mic that is too sensitive for the input stage of the transmitter.

It WILL show a clip of the input of the beltpack. I have seen it happen on QLXD1 with Audio Technica ATM350 mics. It's a separate symbol on the display of the receiver. This is independant of the gain setting of the receiver.

It shows TxOL on the display by the level meter.
« Last Edit: March 25, 2019, 03:26:50 pm by Mark Rombouts »
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Zachary Sherman

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #22 on: March 25, 2019, 09:59:08 pm »

Sorry for taking so long to respond again! I'll respond to comments in order.

Russell: Interesting... definitely something to think about. I hadn't thought about the mic possibly being over-driven before going into the pad, but it totally makes sense. I just figured the pad control was "moved" to the receiver instead. When I get a chance at school, I'll see if I can test this. Our mics are the high sensitivity versions, so this could be the issue. The only other show we've done with the QLXD1's since moving from the ULX's was a play, so no music involved and actors spoke more quietly. You might have hit the jackpot!

Kevin:
- I do the same for strain relief. Since I mic on the left side for kissing/hugging purposes, I ask actors to turn their head all the way to the right before taping on their neck. That way, they've got all the capability to move their head they need.
- Your tip about putting tape on before makeup then mic'ing after is GENIUS! I think I'll do that for the next show I work on.
- [Your third paragraph] This is what Russell was saying too, and it seems to make a lot of sense. I'll try the test you suggested when I get a chance and I'll report back.
- During the show, the person mixing can't see the receivers. We know it's not ideal, and we're actually "renovating" our sound booth area very soon (hopefully >one month) to make it more efficient. I've attached a picture of what it looks like now, a superimposed image of the design for the new part, and a diagram of the benefits of this new plan. Although it looks like there's a wall right next to the ear of the person mixing, in actuality the sound isn't impacted by this.

Mark: I'm going to try your suggestion. I had tried it in between shows when the run was still going on and that didn't fix the issue, but I'll try it again, yelling louder.

Kevin again: Yes! This is exactly what happened to us. I'll try your test and report back.

Eric: I agree, it's seeming more and more like this is related to the problem. Based on what Russell and Kevin said, it seems like the issue is that I can't pad the mic's level down before it goes into the pack's preamp. This could definitely cause my issue!

Kevin again again: Yep, your analogy seems just right. Like the camera op, I never saw an issue with my meters, since I wasn't looking at the mic's meter (I figured it was mirrored on the receiver, which wasn't peaking, but I didn't know about the mic possibly overloading the pack's preamp before the signal even got to the receiver).

Guys, I think you might have figured it out! Thank you so much for all your suggestions. It's really fun and educational for me to hear your thoughts and conversation on the forum.

I'll test out some of these suggestions and report back on how the tests go. If you have other questions about our setup, just ask!
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Loren Miller

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #23 on: March 26, 2019, 11:49:12 pm »

Are the antennas combined and in a place where there is clear line of sight? Or do you have a million antennas mounted in the rack underneath where everyone is sitting?

Loren
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