Jump to content


Photo

Feedback Reduction Barely Working


  • Please log in to reply
33 replies to this topic

#1 KeefPilchards

KeefPilchards

    Just Startin'

  • Members
  • Pip
  • 28 posts

Posted 02 July 2013 - 11:51 AM

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


  • 0

#2 KeefPilchards

KeefPilchards

    Just Startin'

  • Members
  • Pip
  • 28 posts

Posted 04 July 2013 - 03:58 AM

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.


  • -1

#3 litesnsirens

litesnsirens

    Gear Head

  • Members
  • PipPipPip
  • 885 posts

Posted 04 July 2013 - 09:56 AM

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.


  • 0

#4 tochiro

tochiro

    Iknowathingortwo

  • Members
  • PipPip
  • 236 posts

Posted 05 July 2013 - 01:13 AM

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.


  • 0

#5 KeefPilchards

KeefPilchards

    Just Startin'

  • Members
  • Pip
  • 28 posts

Posted 06 July 2013 - 11:57 PM

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.


  • 0

#6 litesnsirens

litesnsirens

    Gear Head

  • Members
  • PipPipPip
  • 885 posts

Posted 07 July 2013 - 07:46 AM

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.


  • 0

#7 tochiro

tochiro

    Iknowathingortwo

  • Members
  • PipPip
  • 236 posts

Posted 07 July 2013 - 10:02 AM

It seems I have to bring my M20D back to the shop then because the FBS is activated, the acoustic guitar feeds back on the low A string for several seconds and nothing happens.
  • 0

#8 Ruben40

Ruben40

    Just Startin'

  • Members
  • Pip
  • 75 posts

Posted 08 July 2013 - 12:48 AM

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.


  • 0

#9 Octo777

Octo777

    Gear Head

  • Members
  • PipPipPip
  • 880 posts
  • LocationKeith, Scotland

Posted 08 July 2013 - 05:54 AM

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.


  • 0

#10 kmachman

kmachman

    Just Startin'

  • Members
  • Pip
  • 63 posts

Posted 08 July 2013 - 10:08 AM

It's 12 frequencies over the whole mix, which in most situations should be able to take care of any feedback issues. 

 

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


  • 0

#11 litesnsirens

litesnsirens

    Gear Head

  • Members
  • PipPipPip
  • 885 posts

Posted 08 July 2013 - 10:40 AM

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.
  • 0

#12 tochiro

tochiro

    Iknowathingortwo

  • Members
  • PipPip
  • 236 posts

Posted 08 July 2013 - 11:55 PM

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...


  • 0

#13 antonioctd

antonioctd

    Iknowathingortwo

  • Members
  • PipPip
  • 103 posts

Posted 09 July 2013 - 03:54 AM

Well, all I can say is that since I've been working with the M20d I never had to even think about feedback again... :rolleyes:

 

So yah Tochiro, there must be something very wrong there!


  • 0

#14 tochiro

tochiro

    Iknowathingortwo

  • Members
  • PipPip
  • 236 posts

Posted 09 July 2013 - 04:55 AM

Please Line6 could you tell me whom I should contact for that problem?  I bought it in France.


  • 0

#15 silverhead

silverhead

    Uber Guru

  • Line 6 Expert
  • 11133 posts
  • LocationOttawa, Ontario, Canada

Posted 09 July 2013 - 05:42 AM

You can open a support ticket here:

http://line6.com/sup...ickets/add.html

 

...... or contact Line 6 UK directly at the number that appears at the bottom of the above page/link. I believe that number serves Europe, not just the UK.


  • 0

Life is what happens to you while you're busy making other plans.
.... John Lennon

 

 


#16 tochiro

tochiro

    Iknowathingortwo

  • Members
  • PipPip
  • 236 posts

Posted 09 July 2013 - 06:17 AM

Thank you. I've just opened a support ticket. OP, how was your latest gig? Still the same problem?


  • 0

#17 KeefPilchards

KeefPilchards

    Just Startin'

  • Members
  • Pip
  • 28 posts

Posted 18 July 2013 - 01:46 PM

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.


  • 0

#18 litesnsirens

litesnsirens

    Gear Head

  • Members
  • PipPipPip
  • 885 posts

Posted 18 July 2013 - 04:10 PM

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.


  • 0

#19 tochiro

tochiro

    Iknowathingortwo

  • Members
  • PipPip
  • 236 posts

Posted 19 July 2013 - 10:56 PM

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.


  • 0

#20 KeefPilchards

KeefPilchards

    Just Startin'

  • Members
  • Pip
  • 28 posts

Posted 20 July 2013 - 06:42 AM

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!


  • -1




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users