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Feedback Reduction Barely Working


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Hi all!

 

I had my first rehearsal using the M20 last night.  It's a four-piece folk/acoustic lineup.  We're using two LD MAUI11 compact line arrays for speakers, and overall the sound was excellent.

 

One particular problem I had was with the feedback reduction.  We use a DPA 4099 clip-on condenser mic on the violin, which can sometimes be a challenge with feedback.  In the past I've successfully notched out the worst frequency with the parametric EQ on a Bose T1 mixer, but I was looking forward to seeing how much better the automatic reduction would be on the M20.  

 

Sadly, it completely failed to deliver.  I auto-trimmed the input gain, and then cranked up the master.  Very loud feedback ensued, at multiple frequencies.  The FBS was on, and I tried resetting it and switching between vocal and universal setting.  After trying for some time, it hadn't found a single frequency.  My ears did though- it was very loud, with very easily discernible individual frequencies.  A bit later it did pick out a couple of lower frequencies (ie the red lines appeared on the chart), but it made no noticeable difference to the feedback.  As it stands, this renders the DPA mic completely unusable, which is hard to take since the per-channel FBS was the main reason I went with the M20 in the first place.

 

I also tried this same operation earlier with an AER acoustic amp and an SM58 with basically the same result.  No apparent attempt from the M20 to cancel any feedback frequencies.

 

Am I missing something?  Is anyone else having problems or could my unit be faulty?  It has the latest firmware.

 

Thanks

Keef

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I guess nobody has any ideas on this?

 

I have a gig on Saturday, so this'll be the first chance to try FBS in a real performance setting.  Will see how it goes and report back.  For this gig we'll be using a Headway Band pickup on the fiddle instead, as it's more feedback-resistant.

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The M20d should be able to notch out 12 different frequencies.  The difference between the vocal and universal is just how aggressive it is, you would use universal on instruments that may use fairly long sustained notes that don't have a lot of variance since that is what the FBS is trying to find and notch.  You said that you noted the red lines, how many did you see?  If there were already 12 frequencies notched then you may have maxed out before the DPA 4099 could be picked up.  Every time you shut down the M20d all your FBS settings are lost.  I have actually put in a feature request that Line6 update the firmware to allow us to save the FBS settings with setups and then perhaps assign a clear FBS function in the tweak mode.  That way if you find that you are having troubles with the same frequencies in a given room you can save a setup for that room and if you need to start over you can just clear the FBS settings without shutting off the M20d and then turning it on again.

 

When you start to ring out the room, how about trying it with every thing except the DPA 4099 muted.  Ring out that mic first so you can make sure that problem frequency gets found and notched and then un-mute everything and let the M20d find whatever else it can find then when you turn the volume back down to the level you're actually going to be playing at you should be good to go.

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I have the same problem as the OP.  What's the procedure then?  For each input, should I increase the PA output volume until there's feedback so that the FBS learns the right frequencies for a particular room? 

 

If I only plug my acoustic guitar with the FBS enabled (even on the Vocals setting), when I increase the PA volume there's a low feedback (the low A string of the guitar) rather quickly and the FBS does nothing - the FBS on or off it's the same thing for me and no red line appears...  How come?

 

Thank you.

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I thought there were 12 frequencies per channel, not over the whole mix?

 

Anyway, I've tested this in the simplest possible way - with a single SM58 and one speaker.  It feeds back pretty much unrestrained.  I might see at most three or four frequencies appearing (the red lines), but they don't seem to make any difference to the feedback that's occuring.

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It's 12 frequencies over the whole mix, which in most situations should be able to take care of any feedback issues.  It has for me so far. Given the chance I will ring out the room, open up all the mics and crank the volume until band after band of feedback fades in and then gets choked by the M20d.  If I keep it going and keep cranking it I could probably exhaust all 12 bands but I'm guessing that the first 4 or 5 are all that would actually ever cause any problems at actual playing levels.  Once I turn the levels back down to playing levels I don't even hear a hint of feedback for the rest of the night.  Technically you could argue that I should only ring out the first 4 or 5 so that the notching doesn't affect the overall sound but I have never found that to be a problem what gets notched out is such a thin sliver that it doesn't affect the overall mix to a noticeable degree.

 

If during your testing you aren't hearing the feedback come in and then within a few seconds disappearing, there must be something wrong.  I say that based on the test you have described and the fact that you have explained enough in your previous post that it's unlikely, although I guess remotely possible, that you are overlooking something.  You're checking to make sure that the FBS is activated on the channel that you are testing, narrowed it down to a single live mic, cranked the level so that the feedback is really strong and constant for a long enough duration that the M20d can recognize it and notch it out.  I don't know what else to suggest there must be something not working properly.  I wonder if re-installing the firmware might bring it back online.  One of the Line 6 guys will see this soon and offer better suggestions than I ever could... Hang tight.

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I had several live feedback situations, where the FBS was not working at all.

e.g. acoustic guitar feedback.
I also made several tests to examine the feedback problem and its algorythm.

 

For me it seems that the signal level of the input channel has a big influence, if FBS is working correctly or not.

My opinion: If the signal is too hot, then the FBS has problems to detect the feedback frequency.

 

Try to lower the input gain of the channel and repeat your test.

 

For me the FBS system is not usable in live situations,

because you cannot be sure that your input signal is always in the right condition for the FBS system.

 

Therfore I do not use the stagescape FBS anymore.

Instead I use the SABINE feedback system without a problem.

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I find the above situations where the FBS isn't working very curious.

 

I've used my M20d rig in various setups, with as many as 3 L3m's (1 as a monitor) and 2 L3s's and other Behringer monitors hooked up and only once have I ever had any issues with feedback but that was due to my vocalist turning on a Megaphone type effect on her vocal processor which we forgot to test, and were able to adjust afterwards.

 

I've very much been literally able to set up and go whether it's been full bands or just acoustic stuff.

 

To be honest it has been so insignificant that I don't even really know if the FBS has been working on my desk at all.

 

As a rule, I always set my master output on the desk to 0dB and make sure all the speakers are set at unity volume on their master controls. All levels are then controlled via the channel levels.

 

Might it be that some of you are simply driving things a bit too hot and expecting too much from the desk? It's amazing what dialling things back a couple of dB's can do for a mix.

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UNTRUE!!!! It is 12 frequencies for each channel!!!

You are correct!!!

 

I had asked this and had it answered...

I was a little confused about the reply though

Apparently channels 1-5 share the same algorithm

And 6-12 share one. Not sure if that is just to save channels having to duplicate notched frequencies.

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I set my master output on the desk to 0dB, the input trim are automatically adjusted by the M20D but my acoustic guitar feeds back and the FBS (on vocals or instruments) does nothing... (no red lines).  I can switch the FBS on or off and nothing changes. 

 

I also tried with my Shure SM58 microphone and the FBS is also useless in that case.

 

There must be something wrong here...

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  • 2 weeks later...

Hi all

 

Have been away for a few days, hence not checking in to this thread.

 

I've only used the M20 for one gig so far.  We used the Headway pickup for the fiddle, and didn't push the volumes.  I think I kept out of the feedback zone using that method, and hence didn't really try the FBS. 

 

There was one section in the gig when we invite audience members to come up and sing a few lines.  Typically this means people with no mic technique (ie not close enough), and with fairly weak voices.  I had to push the volume up during that section, but feedback started to creep in, hence I couldn't get it as loud as I would have wanted.  So, from that I conclude that the FBS wasn't really doing anything.

 

We have another gig tonight in a larger venue, so levels will probably be higher.  No audience participation for this one, but I'll be keeping my fingers crossed we get through it....

 

From the other responses it seems this feature either works very well, or not at all.  I wonder what random factor is at work here?  One thing I do know - I'll be raising a ticket and requesting a replacement desk as soon as I have a clear time window with no gigs.

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Well when you say feedback was creeping in.  The FBS isn't going to fix anything under those circumstances.  In my experience with this board it needs a solid feedback signal to occur for a couple if seconds in order to identify it as feedback and then notch it out.  That creepy feedback that is just kind of on the edge as you sing can't get picked up in this manor.  That's why whenever I can I go into the room I'm playing when there is next to no one there and ask if I can ring out the room for a few seconds.  Then I make sure all the mics are live, crank the volume up past where I intend to have it for the show, and slowly bring it up til the system starts to feedback.  I let it do it's thing, 1 by 1 identifying the frequencies and then silencing the feedback and then I turn the volume back down to playing levels and I don't have to worry about it anymore.  But don't turn off the m20d or you'll have to start all over again.  I've made a feature request to be able to save FBS settings with the setups or presets... still waiting on that though.

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I've found that the FBS does not work with some instrument presets.  For instance it did not work with my acoustic guitar because I had selected the Stereo direct as a preset but when I changed the preset to Acoustic Mic'd it worked.

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Well, here's the report from last night's gig:

 

Sad to say, it let me down big-time  :(

 

I tried ringing out channels before the gig, but I had lots of problems despite this:

 

Acoustic guitar - fed back every time I left the strings unmuted.

 

Percussion (basically a bass drum and other bits being picked up by a PZM boundary mic).  Lots of low-frequency feedback that was loud and very obviously monotonic (ie surely easy for an algorithm to identify).  During soundcheck I even let this run solo'd at very loud levels, and there was no sign of the feedback being notched out at all.

 

Vocal mics - we had a couple of cabaret-style singers performing before us.  Both these guys were standing a bit closer to the speakers (LD MAUI 11 Line Arrays) than was ideal, and they both got occasional bursts of feedback, which only stopped when they moved away.  No apparent difference vs using a standard "dumb" analogue desk.

 

Due to all of the above I had to keep the overall level a lot lower than I would normally set it, which detracted from the gig quite a bit.  Also the iPad connection was refusing to work, hence I was powerless to help when the other guys were on stage.

 

All in all, the bottom line for me is that the three main USPs of this mixer are just not working properly, i.e.:

 

  • Feedback reduction
  • Multitrack recording
  • Wireless mixing.

 

I'm just going to take it back to the shop and ask for a replacement unit.  There are too many faults here for me to want to start troubleshooting them individually with Line6 support.

 

I'm still convinced this is the best solution out there for what I need though.  I just hope the replacement unit is better!

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  • 1 month later...

You wouldn't be able to actually "hear" it set any filters.  They are too narrow for human hearing to detect.

 

Feedback management is set on the input  page in deep tweak.  It is automatically assigned to those inputs that typically have problems but not set to all presets (e.g. electric guitar settings).  You want to use it in the universal setting if you are running any music through the mixer.

 

I would suggest as a start you make certain that your mixer is running the most current version of the firmware.  It is available on the downloads tab from the main Line 6 page.  Secondly create a new setup just in case somehow a switch was set in the wrong place.  Try a test with a single mic (vocal preset).  Switch to the input tab while in deep tweak and you should be able to see it set filters as you bring the system up into feedback.

 

That said, there is a limit to how much it can do and feedback will occur with all systems.  This will depend on your exact system, its layout and the acoustic space you are trying to work in.  Typically you can expect 3 to 12 dB improvement in gain before feedback.

 

If you are also using Line 6 speakers I would recommend shutting the Feedback switches to off and let the mixer do the work.

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I think another thing to consider with instruments is that there is a difference between the type of feedback you get with a microphone squelch and an actual note of an instrument feeding back, such as a guitar note. When you hear a mic feedback it truly sounds mono tonic like a sine wave. I've had more problems in he past with any system trying to tame a low G, G# or A on an acoustic guitar. But that to me actually sounds more like the guitar note itself building up including harmonics which is going to be far more difficult to tame because its far more complex and the M20d really does thin notches so that it has the least amount of effect on the overall EQ of your mix. When drums ring and then feed back I suspect it's the same sort of thing, more complex than a typical mic.

As Don points out you need to use less aggressive FBS settings for instruments (universal) or you'll get some weird side effects happening. For the acoustic guitar issue I would try using the PARA EQ to try to tame it... They tend to be too boomy anyway on he lower strings. Depending on what notes are actually feeding back either notch them (likely somewhere between 185 and 220hz) or even try a gentle shelf EQ from 220hz down and lower the whol range til you get a nice even sound, which should help deal with the feedback as well.

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  • 7 months later...

A suggestion that I would offer when chasing down feedback.  Mute the other channels when ringing in a particular channel.  I can't tell you the time that I've spent trying to get rid of feedback on one channel, only to find that an open mic or instrument somewhere else on the stage was actually feeding back while I was trying to dial in the first channel.

 

Now I start by muting all the other input channels.  Getting control of the feedback on the channel that I'm working on, then as a last step, unmute each of the other channel one at a time.  If you get feedback when un-muting one of the other channels, then you can start on that channel for your next channel to test.  Mute all of the other channel and repeat.

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I have no solution for the FBS not working, but just want to throw in some thoughts on feedback issues:

 

I found out that using Line Array type of Speakers are VERY prone to feedback (No matter if using an analogue Soundcraft desk, a behringer Xenyx something analogue desk or the M20d), just hold a mic or acoustic guitar somewhere near the speaker (even 30-40 centimeter will do the trick, no matter if on the side or behind the speaker) and off goes the typical "hummm" or "hiss".  At the Moment we are using H&K Soundcaddys. As said before until last year we gigged with an analogue Soundcraft EFX-8 from one of our guitarists and now with my M20d. We had feedback issues every time during our last gigs, no matter if using the new M20d or the old desk. Mainly the feedback is coming from one of the acoustic guitars which is using a combination of Piezo and microphone pickup. Unfortunately we cannot get the guitarist away from using one of the soundcaddys also as his monitor and he is always sitting just on the side of the soundcaddy. Bad augury, I know.

BUT: I used the preset for acoustic guitar direct for his Martin, which was not having ths FBS on the channel strip. Changed that to acoustic mic´d preset, which is featuring the FBS on the Strip by default. Looking forward to hear the difference at the next gig.

 

I´m also looking Forward to buy some L3T and use these on our gigs. Hope it will be a big improvement over the Soundcaddys, because our Soundcaddy Line Arrays are not designed to work as monitor AND FOH at the same time IMHO  :)

 

So, my conclusion is: OUR feedback issues are related to combination of ignorance, too less knowledge of the M20d and not the right use of our equipment, and isn´t really to blame on the M20d or the FBS built-in. Nevertheless our Sound has improved tremendiously since using the M20d :)

 

What we did and will do once again in the next few weeks is a technical rehearsal where we are going to test some new setups I have created and just Play around with all the Options the M20d offers until everyone in the band is satisfied with his and the Overall Sound of FOH and monitors. We can Play around without time pressure during the soundcheck before a gig. Maybe this is also an Option for you to just get together with the band and Play around with your Options until everyone in the band is satisfied and you can reduce or even eleminate feedback issues. At least this will give you a good Basic Setup for the next gig with only a little (or in some venues a little bit more)  tweaking necessary.

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If switching the piezo channel to include FBS didn't help much then you have a very difficult problem. That would mean that the sound back to the guitar is so loud that is is resonating the body back into the saddle pickup.  Have you tried a Feedback Buster plug in the sound hole?

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Feedback is inevitably the root of all evil for us hobbyist sound techs with our M20's but ultimately, it is generated when our on-stage volume is typically higher than needs be. I hate to say it but guitarists and bassists are the worst... They set the stage levels with their backline then the singers grumble because they can't hear themselves, so the monitors get pushed up and up... hey presto whistles galore.

 

Get your backline players to reduce their on-stage volumes AND direct their cabs away from FOH so it is there purely for them. Now try doing an initial soundcheck with just vocal monitoring and backline (leave the FOH off at this stage), getting the monitors to a point where your singer(s) are happy. If you then "push" the monitors up an extra 5-10db with singers in place behind their mics, you'll likely induce the worst of the feedback frequencies for the M20 to notch out and can then drop the levels back down. Then record something.

 

The last time we ran the rig out, we did just that. Singers happy and on-stage levels sensible. We then did a basic mix in headphoneswith the recording before heading out front with everyone to tweak the mix and set FOH levels. Aside from a few inevitable whistles early doors ( as the room acoustics had changed with people) the M20 notched out the extra frequencies pretty quick. We were complimented on two fronts... how good we sounded AND on how sensible our overall volume was. Loud enough to be enjoyable but not so loud that people had to shout to each other to be heard.

 

My only gripe at present is a bass player who tweaks his bass guitar volume control during the set... we've a full gigs worth of recordings where his levels start out great but by the end of the first set his input has got too hot and is distorting.

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I agree. I constantly battle with our guitar player. He claims he is not louder than the drums. I tell him to put his amp beside him and point at his head! But guitar players generally don't like to do that. They feel they need the tone of their amp. They have no faith in the front end sound apparently. At least, this is many of the guitarists I have played with. But not all. I have met a couple that use their amp as a monitor for themselves. We are a four piece. 3 of us use IEM. No need to mention who doesn't use an IEM! So he has an L2m as a monitor. I have stopped bringing a bass cabinet and run my bas direct. We mix it into our IEM's and I put my bass through the (non rattling) L2m. So we have made huge progress. Trying to get the drummer to move to E-drums. He is close....just not in the budget for him yet. But, at least he is willing. That is a start.

 

But I totally agree. Feedback is drive by people being too loud, and often the guitar player (waaaay more than us bass players!). Then the vocal wedge is never loud enough.

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@dboomer: Yes, I have told our guitarist to use feedbackbusters, but he refuses also to use this Little helper. He think´s he is too quiet then.... *sigh*

 

@digital-Sound: Introduce your Drummer to this:

http://www.schlagwerk.de/produkte/cajinto-yambu/cajinto/booster-set/

 

I promise, he will be A LOT quieter :D

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I agree. I constantly battle with our guitar player. He claims he is not louder than the drums. I tell him to put his amp beside him and point at his head! But guitar players generally don't like to do that. They feel they need the tone of their amp. They have no faith in the front end sound apparently. At least, this is many of the guitarists I have played with. But not all. I have met a couple that use their amp as a monitor for themselves. We are a four piece. 3 of us use IEM. No need to mention who doesn't use an IEM! So he has an L2m as a monitor. I have stopped bringing a bass cabinet and run my bas direct. We mix it into our IEM's and I put my bass through the (non rattling) L2m. So we have made huge progress. Trying to get the drummer to move to E-drums. He is close....just not in the budget for him yet. But, at least he is willing. That is a start.

 

But I totally agree. Feedback is drive by people being too loud, and often the guitar player (waaaay more than us bass players!). Then the vocal wedge is never loud enough.

Our guitarist, if anything, is the opposite and often has to be told to turn up a tad on stage.

He uses an Egnater Tweaker and has the extension cab. The main cab is fired sideways off stage with an SM57 in front of it, fed to the M20d and he then has the tweaker extension cab on an angled stand firing back at him like a monitor from front of stage. As a result, his backline doesn't have much impact at all on the FOH levels as it isn't contributing to the sound projected from stage. Our bass player on the other hand...

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@dboomer: Yes, I have told our guitarist to use feedbackbusters, but he refuses also to use this Little helper. He think´s he is too quiet then.... *sigh*

 

@digital-Sound: Introduce your Drummer to this:

http://www.schlagwerk.de/produkte/cajinto-yambu/cajinto/booster-set/

 

I promise, he will be A LOT quieter :D

Actually, our drummer isn't too bad at all. Just our guitar player. But we have him in control....just have to have a leash on him all the time! Not allowed to run free!

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@dboomer: Yes, I have told our guitarist to use feedbackbusters, but he refuses also to use this Little helper. He think´s he is too quiet then....  

 

He may think he's too quiet but his guitar/piezo system thinks otherwise.  It's true that he might not be loud enough to be heard but feedback doesn't care about that. :)

 

Here's what feedback actually is ... he plays a note and that note goes through the system.  The system sends it out in the air and some of it gets back to his soundboard and piezo where it gets picked up and sent back out.  If it gets there at a lower volume then it went in then it gets sent through at a lower volume and as you can see quickly dies out.  But if it gets back at equal volume or louder then when it was originally played the next time it gets picked up and set through it comes back even louder and it will keep building and building as the loop continues.

 

Usually the frequency response of these loops is not perfect and the FBS works by pulling out some of the peaks (which are very narrow).  Once the FBS has pulled out a number of narrow peaks and only wide peaks are left it stops being helpful because at this point it would simply be turning down the overall volume.  So FBS is helping some but not as much as you need it to.

 

So in his case the soundboard is concentrating the regeneration in one big group and there is nothing electronic that can fix it. He can either turn down, move father away from his monitor so the sound from it won't get back to it as loudly or make some mechanical compromises to de-tune the problem.  He has no other options ... well, or switch to electric  :D

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Actually, our drummer isn't too bad at all. Just our guitar player. But we have him in control....just have to have a leash on him all the time! Not allowed to run free!

 

You need a leash for the guitar player? But how do you keep the drummer from wandering off into traffic? They're easily confused... :P

 

 

 

 

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  • 1 month later...

I have a different, but related question: My rig is 2 L3t, 2 L3s, 2 L2t (used as monitors) and the M20d. My question is, do the feedback suppression buttons on the speakers make any difference when running the rig using the M20d or are these bypassed in favour of the FBS built into the M20d?

 

Also, one slightly unrelated question: I thought the units were supposed to automatically configure themselves as monitors when laid on their side. My L2t don't do this and I have to set them to monitor mode manually. Is this a fault?

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They're not specifically bypassed, but will not aid anything if turned on IF you're using the M20d hooked up via L6Link.

 

Can't answer you as to what's wrong with the gyroscopes, though it would seem odd if both were duff. Do you power up and position, or position then power up? When looking at Manage L6Link Devices, how does the M20d report your L2's? Is auto configure turned off?

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