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feedback exterminators (?)

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Anonymous
March 11, 2005 6:48:58 PM

Archived from groups: rec.audio.pro (More info?)

hello,

let's say you're playing a small club gig with a mackie mixer and a
rock band, and you don't have a sound guy to man the mixing board.
besides gain-staging as best you can, you want to patch in one or two
"feedback exterminators" to provide some insurance against howling.

a few questions:

1) where is the "classic" place to put one? (a channel insert, between
the main outs of the mixer and the power amp, etc.)

2) do these things actually work?

3) is there a sonic artifact issue? (chokes off high frequencies, adds
intermodulation distortion, etc.)

4) what's a good "industry standard" brand, without being something
like $2000?

5) any other basic things to know?


thanks for any insights.

More about : feedback exterminators

Anonymous
March 11, 2005 11:00:32 PM

Archived from groups: rec.audio.pro (More info?)

<genericaudioperson@hotmail.com> wrote in message
news:1110584938.275683.53870@f14g2000cwb.googlegroups.com...
> hello,
>
> let's say you're playing a small club gig with a mackie mixer and a
> rock band, and you don't have a sound guy to man the mixing board.
> besides gain-staging as best you can, you want to patch in one or two
> "feedback exterminators" to provide some insurance against howling.

I'll spare you the rant about asking sound techs about how to use bullshit
gadgets to do our job.

FBX units mangle sound quality. I would only ever use them for monitoring
under especially troublesome condiitons, like upright bass on a loud stage.

Feedback is more a matter of acoustics than gain-staging, so you should
focus more on speaker and mic placement, and learn the polar and frequency
response patterns of your mics. Most have a 3-5kHz presence peak which is
generally the first thing to feed back.
Anonymous
March 12, 2005 5:29:09 AM

Archived from groups: rec.audio.pro (More info?)

On Fri, 11 Mar 2005 15:48:58 -0800, genericaudioperson wrote:


> 1) where is the "classic" place to put one?

In the dumpster!
Related resources
Anonymous
March 12, 2005 7:00:56 AM

Archived from groups: rec.audio.pro (More info?)

Zigakly wrote:
> <genericaudioperson@hotmail.com> wrote in message
> news:1110584938.275683.53870@f14g2000cwb.googlegroups.com...
>
>>hello,
>>
>>let's say you're playing a small club gig with a mackie mixer and a
>>rock band, and you don't have a sound guy to man the mixing board.
>>besides gain-staging as best you can, you want to patch in one or two
>>"feedback exterminators" to provide some insurance against howling.
>
the basic fault of a fbx type unit is you need feedback before the work
learn how to set up and tune your rig so it doesn't feedback and you
will sound better, spend less money, and sound better
george
Anonymous
March 12, 2005 9:50:22 AM

Archived from groups: rec.audio.pro (More info?)

In article <1110584938.275683.53870@f14g2000cwb.googlegroups.com> genericaudioperson@hotmail.com writes:

> let's say you're playing a small club gig with a mackie mixer and a
> rock band, and you don't have a sound guy to man the mixing board.
> besides gain-staging as best you can, you want to patch in one or two
> "feedback exterminators" to provide some insurance against howling.
>
> a few questions:
>
> 1) where is the "classic" place to put one? (a channel insert, between
> the main outs of the mixer and the power amp, etc.)

Channel insert, on the channels that are likely to feed back, like the
vocal mics. One per mic.

> 2) do these things actually work?

The good ones allow you to get a few dB more gain before feedback
without doing too much damage. The crummy ones work, too, but not very
well at what you're trying to accomplish. How do you tell them apart?
Ask your banker.

> 3) is there a sonic artifact issue? (chokes off high frequencies, adds
> intermodulation distortion, etc.)

They work by inserting notch filters, so something will be missing
from the audio spectrum. If they're adjusted correctly it will be
fairly harmless, undetectable by the audience, but measurable. If
they're not adjusted properly, or you let them run wild, they're
likely to filter out something that's not feedback now and then.

> 4) what's a good "industry standard" brand, without being something
> like $2000?

Sabine. They cost like $2,000.

> 5) any other basic things to know?

Don't bother unless you're willing to spend what it costs to get one
that works pretty well. Just turn things down or move speakers and
mics so feedback isn't a problem.



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
March 12, 2005 10:12:31 AM

Archived from groups: rec.audio.pro (More info?)

<genericaudioperson@hotmail.com> wrote in message
news:1110584938.275683.53870@f14g2000cwb.googlegroups.com
> hello,
>
> let's say you're playing a small club gig with a mackie mixer and a
> rock band, and you don't have a sound guy to man the mixing board.
> besides gain-staging as best you can, you want to patch in one or two
> "feedback exterminators" to provide some insurance against howling.
>
> a few questions:
>
> 1) where is the "classic" place to put one? (a channel insert,
> between the main outs of the mixer and the power amp, etc.)

Depends what works best. Mike said channel insert, and that might work in
some cases. OTOH, I've been known to work SR with up to 18 mics and that
would be a lot of FBX boxes, even at Behringer prices.

> 2) do these things actually work?

Depends what you call "working". Can they make ringing go away? IME yes. Can
they mangle the sound? IME yes. Can they help if used intelligently? IME
yes. Are they essentially band-aids for problems that are better addressed
by other means? IME yes.

> 3) is there a sonic artifact issue? (chokes off high frequencies, adds
> intermodulation distortion, etc.)

Let's review what a Feedback eliminator is. They are basically notch
filters. They reduce system acoustic gain at frequencies where acoustic gain
is excessively high. They can be static, or they can be dynamic and
automatic. The automatic ones use digital circuits to detect protracted
tones in the signal and program a notch filter to the frequency of the
protracted tone. This begs the question is how does an automatic feedback
eliminator distinguish between a sustained note and feedback? They answer is
that they usually aren't that smart.

> 4) what's a good "industry standard" brand, without being something
> like $2000?

Good question given that many think that there is no such thing as a good
feedback exterminator.

Here's a fair summary of what is available:

http://www.sweetwater.com/store/category/c475

> 5) any other basic things to know?

I think that conventional wisdom is that if you have a fairly static
feedback situation that you can't solve any other way, that a few
well-placed notches can be a big help.

For example, I work with a system where the main speakers are 27 feet above
the platform. The first feedback mode would be about 41 feet. In fact the
system does not have much acoustic gain at 41 or even 82 Hz. The first mode
is at almost exactly 121 Hz where the system must have signfiicant acoustic
gain to sound fairly natural with male voices.

Because the distance from the main speakers to the mics doesn't vary
percentage-wise that much in actual use, the first mode is fairly stable and
shows up with a variety of mics at a variety of locations. There might be a
room resonance that *helps*.

Bottom line is that in this system, nailing the ringing at 120 Hz and about
3 other frequencies provided a nice compromise between tone quality and
system stability. I tried notching out the as many as 10 ring points, and
the last 5 did virtually nothing for system stabilty. I used a straight
up-parametric eq - a Rane SP-15. I think that the system actually sounds
better with the parametric in place set up right, even when it isn't on the
edge of ringing.
Anonymous
March 12, 2005 12:11:47 PM

Archived from groups: rec.audio.pro (More info?)

<genericaudioperson@hotmail.com> wrote:
>
>let's say you're playing a small club gig with a mackie mixer and a
>rock band, and you don't have a sound guy to man the mixing board.

There's your problem.

>besides gain-staging as best you can, you want to patch in one or two
>"feedback exterminators" to provide some insurance against howling.

The Sabine boxes aren't insurance against howling. They still need to
be set up in advance and the filters locked down. It's still something
that takes some care. It's faster to do than doing it by hand with a
parametric or a Little Dipper, but you still have to ring out the room in
advance.

There are people who use the Sabine with all the filters floating at all
times. This first of all doesn't prevent feedback, it just reduces the
length of the howl when the box puts a filter on top of it a couple seconds
after it starts. Secondly, it will also put a filter on anything else that
is a pure tone, like flute notes and deliberate guitar amp feedback.

>a few questions:
>
>1) where is the "classic" place to put one? (a channel insert, between
>the main outs of the mixer and the power amp, etc.)

If you are using only a single box, it's probably between the console
and the amp. There are folks who use them on groups so that only the
vocals go through the feedback eliminator, and this can be a handy thing
too.

>2) do these things actually work?

They do, but they still require a human being.

>3) is there a sonic artifact issue? (chokes off high frequencies, adds
>intermodulation distortion, etc.)

If you set it up and leave it alone, they have no serious artifacts. But
you need to have it ring the room out, set the notch filters, and then play
something prerecorded back and listen to it to make sure there's nothing
nasty going on. Sometimes you might want to drop one or two of the filters
that it has decided to put in, depending on how it sounds. They are not
set-and-forget boxes, really.

>4) what's a good "industry standard" brand, without being something
>like $2000?

The Sabine units are basically the ones everybody seems to use. They make
some cheap boxes with only a couple filters that go into inserts, and they
make some expensive ones that have a whole bunch of filters but also can
be a crossover, a delay, and an equalizer as well at the same time.

Before these things came around, you'd see people with an Orban 622 or a
Urei Little Dipper doing exactly the same thing by hand. I can do it by
hand in about ten minutes and I'm not really practiced at it.

>5) any other basic things to know?

They aren't a substitute for any of the following: tighter microphones,
proper mike technique, good PA operators, proper speaker placement. Address
all of these problems first before going the notch route.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
March 13, 2005 11:30:42 AM

Archived from groups: rec.audio.pro (More info?)

thanks for all the insights everyone
!