RTA in eq section?

[RoyParticipant]

Can someone explain why the GEQ is not best for killing feedback? I use it quite effectively for ringing out monitors as I can be a bit more surgical about it. The PEQ surely doesn’t give you quite as many points to cut where required (although it’s good for ID’ing offending frequencies). That said, I’ve created my own presets for wedges (flat environments and reflective environments) that works for pretty much 95% of the time as I find the same offending frequencies popping up.

[Dick ReesParticipant]

[b]Can someone explain why the GEQ is not best for killing feedback? I use it quite effectively for ringing out monitors as I can be a bit more surgical about it.[/b]

1. You can’t “kill” feedback. You can either deal with the causal factors up front or apply some palliative adjustments to compensate for out-of-balance factors.

2. “Surgical” implies precise, narrow cuts. One octave wide GEQ filters are pretty much the opposite of “surgical”. Although your typical GEQ is qouted as “1/3 octave” units, the 1/3 bit applies only to the center frequency of the one octave wide filters.

Causal factors involve quality/pattern of your wedges, placement, mic polar pattern and such, but the bottom line is always “loudest sound at the mic wins”. Poor quality monitors, poor placement and unrealistic expectations from the person at the monitor are commonly addressed by gutting the frequency spectrum with GEQ. Unfortunately, making the performers wedge/position safe from feedback sacrifices headroom and thus monitoring capability output-wise. An apt analogy here is that fixing monitor feedback/headroom at the end of the chain with GEQ instead of addressing quality, processing and placement is like the difference between applying a tourniquet instead of sewing up the wound.

[b]The PEQ surely doesn’t give you quite as many points to cut where required (although it’s good for ID’ing offending frequencies). [/b]

Typical PEQ gives you four bands. Prevailing standards say that if you have to apply more than four filters you need to go back and figure out what’s wrong in the first place. If you’re thinking that GEQ is good because you use fewer filters, remember that the filters are very wide, fixed-width filters and applying them in place of a variable width/center PEQ filter essentially removes more desired frequencies than undesired frequencis. IOW, the baby has been tossed out with the bath water.

If you prefer wide filters, you can always widen the PEQ filters, but you cannot narrow a GEQ filter. Having the option should obviously be preferable. Again, if you find the need to use copious amounts of ANY type of EQ, you have more serious problems which need to be addressed up front, not at the output end.

[b]That said, I’ve created my own presets for wedges (flat environments and reflective environments) that works for pretty much 95% of the time as I find the same offending frequencies popping up.[/b]

This is preferable. I use coaxial monitors as I find they have a smoother, tighter output pattern to start. The wedges themselves have DSP which I’ve spent time optimizing for my use. I have several presets saved for varying program requirements.
I also have several presets stored in my Qu. None of these involve GEQ, just the needed PEQ and occasionally a bit of delay.

To sum up this long reply, using GEQ instead of PEQ is often likened to using a chainsaw to trim your fingernails.

[RoyParticipant]

Really good explanation – thanks Dick.

Out of interest, your use of delays in monitors – is that a stylistic decision or something more scientific? The one time I tried this the vocalist hated so never did it again.

Roy

[AndreasModerator]

A tiny delay (few mSec) may help to eliminate higher pitched feedback, since it shifts the resonating spots to lower frequencies (which may be cut by simply low shelf/cut on monitors).

[Dick ReesParticipant]

Roy…

I mentioned delay as a tool along with PEQ. WHERE you apply the delay was not specified, but I see it got your attention. Remember, feedback loops are a SYSTEM phenomenon, so you have many variables to juggle and we’re not talking about FX delay, rather input and/or output delay.

Feedback occurs at specific frequencies. Notch that frequency and you’ve gained (or ceased to diminish) headroom. But since each frequency has a specific wave length, if you change the distance between the mic and the speaker by, say, a quarter wavelength, the offending frequency will cease to set itself off into the self-reinforcing loop. Of course, some other frequency may then take off…

Delay (channel input delay, mix output delay, mains output delay) can effect a virtual change of distance. If you’re working in a small space or suffer from severe reflectivity, your mains and monitors are going to reinforce/cancel each other in a touchier relationship. As noted, delaying the monitors or monitor content can occasionally bother a vocalist…so try delaying your mains to change the time/virtual distance relationship with the monitors. My experience is that the tiny amount of delay applied for any virtual changes in the spatial relationship should be unnoticeable to a vocalist.

Of course, having mains and monitors with as much EFFECTIVE pattern control as you can afford is where to start, but simply being aware of the variables in positioning and nulls will certainly help without re-investing. But sometimes you just have to accept that certain situations with limited or poor se-up options means you simply will not have as much headroom as you would like. Couple this with musicians who expect YOU to find a technical solution so they can be mindlessly loud or operte at 11 on their amps because “I have to crank it to get MY SOUND, man” and…well, you know the rest.

I use a Qu-16. If I had groups I could get more PEQ/mix by routing a critical MIX via a group. That would give 8 PEQ filters. I’ve never needed more than 4, relying on proper set-up and realistic expectations for system headroom given the laws of physics and the level of cooperation from all concerned.

DR

[RoyParticipant]

Thanks Dick. I find your posts both informative and engaging. I’ve only been doing this for just under a year (around 20 gigs under my belt) and it’s a steep learning curve. Some of the little tricks and tips you pick up on here (your delay tip for example) are priceless.
Roy

[DFTParticipant]

@ Dick Rees and the ‘pitch pipe:’ Thank you! Thank you! Thank you!

I am just a retired guy who started hosting karaoke at several local venues. I’ve Googled over and over and yours is the first cogent lifting of the feedback veil for the ignorati. Much appreciated … and my singers will thank you too!

[Bis-RepetitaParticipant]

Same trick for my subs on mix1, between 2 and 3ms for a 200 peoples gig.
Try it and venues takes some presence.

Also for an instrument, put it 20ms before all others
and it get louder without touching any faders.

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