feedback elimination

noel

Hi

I just purchase recently the drive rack PA and play around the menu and familiarised, the only thing I cant do is removing the feedback. Please explain me clearly in simplest form how to remove the feed back, this is one of my purpose why I purchase this gadget.

thanks in advance,
noel

Dra

Depending on your application. Set the mic on a stand where it (they) will be used. Turn the channel fader down and press FEEDBACK. Select the # of fixed filters and how narrow of band you wish to use.
Speech - widest, but still more narrow than a 31-band EQ fader
Music-low
Music-medium
Music-high - most narrow notch (least noticeble)

Speech responds the fastest, Music-high the slowest.

Slowly increase the mic(s) level until a feedback occurs. When the AFS catches, increase the level a bit more and continue untill all \"F\"s are \"blocked\", then lower the mic level. Select (scroll I think) to Live and select the filter width for those (Sp, M-L, M-M, M-H) and your ggod to go. Play around with different setting and configs to get what you need the most. The \"Live\" filters can be set to auto-release after a set time (5 sec, 20 sec, never, etc).

DRA

Gadget

The idea here is that the mic or mics also be set up, on, and set the way you will be using them for the performance. what we are doing here is identifying which frequencies are a problem as the volume of the system increases. The AFS has to identify a problem so it can fix it.
Gadget

quaizywabbit

if you happen to use a compressor and/or noisegate on your channel inserts make sure you bypass them all when ringing out with the driverack....at the very least shut off the noise gate. Once the feedback filters are set, you can re-engage everything.

noel

Guys thank you for the explanations I will try it again.

regards,
Noel

noel

Hi guys,

Still It can't remove the feedback the AFS is not catching is there a problem on this? all the procedure in the manual is followed on the AFS wizard display. is the built in compressor affecting it because I set it before the feedback. I'm not using anything just mixer, dreiverackPA and amplier. live and fixed filters are also set.

noel

Guys,

By the way I set the crossover, compressor & limiter before I test the feedback wizard is this affecting?

Dra

You should only use the compressor in the rarest of occasions. The compressor needs to be off.

DRA

kpippen

Hi noel,

Compression allows for increased energy to reach amplifiers and loudspeakers, which also increases the possibility of feedback... When the signal goes above a level set on the threshold control, the level of the signal is brought down... This makes the signal quieter overall because the peaks have been lowered... Gain is then provided by the compressor to bring the peaks back to where they were... If you use 6 dB worth of compression you have reduced your margin by 6 dB before feedback, and just a couple of dB could set the system ringing…

Another side effect of full system compression might be the \"dulling\" of sound,…which could be perceived as having less high frequency content... The frequency content of music has a lot more energy in the low frequencies than the high frequencies... When a bass drum is compressed the cymbal hits (which may happen at the same time) are also compressed…

Cheers,

Kevin

Dra

Excellent answer Kevin. Welcome home. Planning on staying long?

DRA

Gadget

kpippen

Dra,

Staying at the Holiday Inn...not home yet...:)

Kev

noel

thank guys for the replies it is a big help? I will try again and off the
compressor.

Fanman20

Hi Guys

Going back to Dra's initial reply my question is:-
Would having someone standing in front of the mic whilst turning channel fader up change the feedback frequencies??
I know that you can induce feedback by opening your mouth wide with mic close to it and feedback can be generated by sound bouncing off your classes! (When levels are raised to just before feedback)
So would a head / body in front of mic change feedback frequencies? Would your head / body \"soak up\" or “reflect� offending frequencies?
Just a thought

Dra

You bring up a valid point. Also to be considered is that when the room fills with people the bodies stop a lot of reflections and absorb some frequencies. The \"hot\" frequencies will change. It would not hurt to have someone stand in front of the mic, but not doing anything to \"cause\" feedback.

DRA

Kyle Abel

When we do AFS, we put a hand in front of the mics to induce feedback, as our heads would do the same while singing. We also only use 3 or 4 fixed filters and allow the live filters to clear after 5 minutes or so. This seems to work well for us...

Gadget

Also consider that the monitors can figure in here as well. The better your system is tuned the less apt it will be to feed back. Remember also that when you increase the volume of the PA, or monitors over the point you set the system up at you change the response of the system and as such you increase the likelihood of feedback.

I set my feedback filters to lift after 5 seconds since the feedback is always moving, and that the feedback eliminator can mistake a held guitar note as a feedback source... wouldn't want the whole note to be nixed would you? BTW an open mouth has a greater feedback potential than a flat hand so cup it an move it around the ball.

Honestly though I never even worry about the feedback eliminator... it rarely crosses my mind since I never have feedback except on stage and with the new 4800 even thats a thing of past. even when a really bad singer with a Shure SM87 condenser came to town...and the monitors were ROCKIN!
G

Kyle Abel

Good points Gadget. I forgot to mention we use IEM, so we rarely have to use the AFS - only when we're on a very tight stage or the mains aren't out in front enough.

Gadget - re: filter lift time, since both of our mics are on stands and don't move, and because we don't have monitors as a source of feedback, would you still recommend a short lift time of 5 seconds? My thought was if we get a troublesome frequency, it would probably would stay a trouble since the mics aren't moving. Although with that logic, it would make as much sense to make the time 60 minutes or whatever the max is... Thoughts?

Gadget

I think if you have a frequency that's that troublesome it would manifest itself immediately and need to be taken care of right away. As I said a properly tuned system doesn't exhibit this type of behavior and the only thing that can really cause this is someone twiddling that shouldn't be. A properly rung out system will be capable of quite a bit more volume before feedback than it has at your set performance level... this is to say that we intentionally go well above concert volume when setting the first few fixed filters. I generally get only one, maybe two to set when I'm quite literally at what would be deafening spl's. No, there isn't any real sound when the process is started except for a brief reminent of a captured frequency, but as I said when you have a flatly tuned system all frequencies should theoretically feed back at the same time should they not?

The problem I see with live music and long hold times is if the feedback eliminator locks on to say a held high pitch note and sets a fairly broad cut ..that frequency will be missing from the spectrum for the remainder of the \"hold\" time. That would then be like taking one of the faders on the GEQ and KILLING it...Now I don't know about you but that ruins the sonic pallet I have worked so diligently to create. Those fortunate enough to have a 260 or 4800 can watch the realtime display of the captured frequency, It's exact frequency center, the amount of cut, and the width of the filter used on the \"suspected frequency\", and the hold time. With only 12 filters to work with, and an infinite number of possibilities, and long hold times.. what would happen once all the frequencies are \"held\"? A nicely run on sentence... chuckle..I have watched ..somewhat amazed for a time a number of filters trigger and fall off till I determined it was distorted held guitar notes.. usually squeals and guess what...wait for it.. here it comes.. FEEDBACK! Necessary feedback, but feedback none the less. The Driverack simply cannot distinguish between necessary and unwanted feedback.

I can see a use for long hold times for spoken word, and pulpit/lectern type situations. Also a long hold time during setup can help identify problematic frequencies... hmmm but here I'm not sure, and I don't have my DRPA here in front of me, does anyone know if you can \"see\" visual reference of the captured frequency on the DRPA? Dra.. you out there buddy? The 260 and 4800 can...and it's useful.

So, tune your system properly flat, maintain a reasonable volume, set the feedback eliminator to catch any spurious frequencies at well above that level, set that rest of the filters live and to short hold times. If you do this you should be able to take a mic right out in front of the speakers and scream your brains out and never have a lick of feedback... I've been doing it for years...

G

Kyle Abel

Thanks Gadget. Excellent post as usual.

Assuming you had a system tuned flat, would room reflections perhaps be a source of feedback? For example, if you were in a small room with a tin roof or walls (extreme example). Couldn't some feedback result? I would expect, as you stated, you would have to be pushing the system or the mics to pretty high levels for this to manifest...

Dra

Excuse me! Pardon Me! Answer coming through! Out of the Way!

The DRPA gives you \"F\"'s and \"L\"'s, then blocks them when active. That's it. Yes, the 260's ability to (at least with the GUI) display the freq and the amount of cut is a great help. And yes, (at least the 260) will combine very close freqs into one wider notch as to not tie up extra filters. Also will pull out a freq -3db then later pull it out -6db using the same filter. Seen it do that, with my own eyes. Don't know if the DRPA can do this or not (doubtfull, but maybe).

DRA

Gadget

Oh yes... reflections can cause this sort of problem...I remember the story of I think it was Dwight Yokum who wanted his monitors bloody loud and the terrible feedback that occurred when got them to the level he wanted... turned out his hat was the problem... the monitor on the floor in front of him was reflecting the sound on to the mic.. an SM 58...with a tighter pattern 58 Beta (a hypercardioid mic) which likes the mic level, and the monitor at 30-35 degrees off axis the problem was solved... But ya if a duct work was in such a position as to reflect the sound to the ON axis part of the mic then ya it could happen.. but sound reflected back to the stage and off you face to the mic... not likely... LF swells are another problem though, and another post...

Gadget
Thanks Dra! you da man!

Hey guys...check out this Amazing Street musician.. It's ... well Amazing!!!

http://www.ifilm.com/video/2887041

kpippen

WOW!!!... That is amazing!!! Thanks for posting the clip Gary... I'm going to forward it to my son...

Thanks!

Kev

Dra

I appreciate the props. I worked hard on that piece. I should have paid the extra money for the second camera. I never signed the release. My counsel will be contacting you soon.

DRA (AKA Eddie VanTwinklefingers)

iwanarock

Hey Dra is that really you ?

If it is, that is outstanding, very well done and very impressive !!

Dra

Sure it is. 8) :roll:

kpippen

Dra uses that \"just for men\" stuff on his hair...