Using an RTA to EQ a venue

Posted: Mon May 22, 2006 5:54 am

How many of you sound engineers out there in the live sound arena use third-octave RTA (real-time analysis) for EQing a venue? This is something I do quite a lot, but I have seen very little discussion of it in these forums.

I'm not talking about tuning up your own studio, but about the times that you land up with your PA/recording gear in a new venue with only a few hours to set up before soundchecks and you need to know if you are in for any surprises on the night.

* Have you found that RTA results give you good pointers as to how the gig will sound with real musicians?

* Do you feel that you can do as good as or better job just using your ears rather than making the effort to do an RTA?

* The venue is empty when you RTA (or soon would be!), but what allowances to you make for the frequency-dependent absorption effects of an audience?

* Have you found makes of RTAs (dedicated or software-based) that are consistently better to use than others?

Posted: Mon May 22, 2006 11:31 am

When I was designing and installing sound systems for theatrical productions, I did it all the time. Flatten with the RTA, and then put on a CD that was similar to what the program was and fine tune to taste. It was also a way to clear the theater when I needed to work. Blast the pink noise and people scatter.

Posted: Tue May 23, 2006 12:18 am

An RTA is a good start point when EQing a system... Use of pink noise and the RTA to get a flat graph will get you a decent sound. The problem is that the frequency response will change in your room depending on where the microphone for the RTA is placed.

What I usually do when I show up at a venue is I ring out the system. With practice, you can get a pretty close system EQ. After that, I play reference music that I know intimately. When listening, I can tell how close the system is. Sometimes I'll use an RTA after ringing the system or after playing the CD to get an idea of how close I am but it really depends... I use it as part of the process to get the system sounding musical in the space.

During the show, an RTA can be a huge help if something gets out of control to tell where that problem is (if you don't have perfect pitch). Plus, seeing all those bouncing lines on the graph just makes you look cool to the audience, too.... Cool

--Ben

Posted: Thu May 25, 2006 11:29 am

yeah, Ben's about nailed here.

I've done a lot of live sound over the years; not too much anymore. I stared in the 70's doing that, with 1/3 octave graphics and RTA's.

My approach was/is about the same: Assuming you're working in a space with a decent/professional system that's set up right (i know, that's a big assumption!), nowadays I bring a CD (or eye-poddd) with music I know and trust. (once upon a time we actually had a reel to reel player at FOH to play tunes...hehehe)

If someone else has set up the system, I do an A/B analysis of the EQ in and out. I have a little pocket sized pink & white noise generator with me as well. (Nowadays, I can run the audio into my laptop w/Sequoia and use the O-scope & graphic viewer, too..)

But dont' fall into the rookie trap: It's not always about getting a "Flat" response. That's not going to happen, and it will indeed change the moment the doors open and people walk in. There's a lot of subjective interpretation to be made, and it's always good to be in touch with the system designer or contractor, to understand what you're looking at, and what it means in context with the rest of the system. (Monitors, in-ears, subs, etc.).

Sometimes it's best to work on an average setting, adjusting as you go, if you're somewhere for a few nights in a row. You may find the EQ will gradually change with humidity and crowd size, sometimes it's even weather dependent. A wintertime concert is going to give you people with heavier, thick clothing, vs. a semi-outdoor venue with lots of loose tank tops and shorts - more bare skin, etc.

Then there's the variables of the venue itself, be it a small club, hockey rink or semi-open shed on a hillside.

I like the current crop of sound system DSP controllers that are all connected via LANs from the powered spkr boxes to a computer at the console. Status and response are all easily viewed right there. With a proper sound check, a really savvy FOH engineer using a wireless card can check spots all over the venue, and dial in some pretty good stuff before doors open, then tweak to taste as the crowds fill it up.

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