# Free RTA



## Schniapereli (Jun 9, 2007)

At my high school, we have a very strange auditorium, with strange acoustics. They once had a professional bring in an RTA, (which came up with some pretty strange frequencies), but since then, our GEQ has been messed up, so now all the notches are just at 0.

I am looking for a completely free or extremely cheap RTA sort of system. I found this online which is (according to my own unprofessional, inexperienced opinion) pretty good.

I also have this little program which outputs pink noise, or white noise, or whatever.

So, I've got pink noise, an RTA, but no measurement microphone. What I'm wondering is, 
can I use a different microphone, and just adjust the system. I could use an SM58 mic (edit,: or rather our MKE-2 since it is omni), output white noise, and fix the EQ to match the picture of the SM58 (MKE-2) frequency respone.

...right?

Is there a better way of doing this? Is there maybe a different program out there that just let's me tell it that I am using an SM58, and the computer calculates it accordingly?

I also have a RadioShack decibel measurement device with a microphone and an output. Is this maybe flatter, and thus better to use as a measurement microphone. (I just don't know how much to trust the quality from RadioShack)

I'm kinda lost here, so any information is helpfull.


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## stantonsound (Jun 9, 2007)

I am not an expert with RTA, as I have only used mine once with my driverack and don't plan on using it again, but it doesn't sound like it will work too well. RTA's and the programs are ok tools, but that is all they are. Your ears are the best tools in your toolbox, so trust them before some piece of equipment. If it sounds terrible, fix it. If it sounds good, leave it alone. 

Now that I am off of my soapbox, see if there is a tech in town that would stop by and use a rta mic for you and set it. Call it a teaching clinic, they will eat it up. The bigger companies will charge you, but a guy with a board that is trying to make a career of it will likely give you a hand.


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## the_dude (Jun 9, 2007)

Unless you are fairly fluent in the ways of utilizing an RTA rig to get the most out of a PA, you're better off doing it by ear. 

Using a 58 will make little bars in your rta go up and down. But If you're trying to get an accurate reading of a room, it will not be enough. A good measurement microphone is encompasses more then just a "flat" response. Other things to consider are the polar pattern, impulse response, and the time the diaphragm come to rest. (I think there's a big word for it but I don't remember.) Earthworks makes some of the best measurement mics around. The M30 is very common, and with good reason. Audix makes the TR40 which (I believe) is about one third the price and about two thirds the quality.


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## kovacika (Jun 10, 2007)

A 58 wont really work, neither will most stock computer sound cards. Behringer makes a decent measurement mic , the EMC-8000. I wouldnt try to use an RTA with anything less than a sound blaster audigy 2 for a internal sound card. Best would be a USBPRE by sound devices but most external usb pre amps will suffice. 
but just as said before, an RTA is only a guideline, use your ears.


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## Hughesie (Jun 10, 2007)

True RTA

is pretty cheap, i got a free copy because of my school

but like all the rest said, i don't use it very much


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## CURLS (Jun 10, 2007)

Bottom line there are plenty of free rta's out there however, there all going to be a bunch of crap without me explaining your waisting your time when it comes to free rta's and you might as well like previously mentioned just use your ear. Quite interestingly though you had he opposite point of view on which microphone to use, omnidirectional is the more optimal choice than a cardiod microphone so yes the mke2 would be better for that application in terms of polar pattern. OH, and another cool audio program that is nice to have is nch tone generator. search for it and you should find it.


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## audioslavematt (Jun 10, 2007)

http://www.redrocksaudio.es/impulse.html

http://www.pensa.fr/freqresplot/index.htm

You want to use the FFT. An RTA is fine to hunt down feedback, but it doesn't take time into account. I'll come back and edit this with a better explanation after rehearsal.


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## Schniapereli (Jun 13, 2007)

Okay, maybe I'll back away from the idea.

The reason I am trying to do this, is that I am still fairly new to tech, and don't trust my ears as much (or jerry-rigging and RTA for that matter). Plus, I just heard that it was some pretty weird numbers, and the guy who originally analyzed the place couldn't remember them, and couldn't really figure it out by ear.

But, I am mainly just trying to explore. It also helps me get a little better at understanding all of the high end equipment, if I can scrap together a pathetic similar one. I'm kinda a hands-on learning person sometimes. I also have no idea how our current state compares to how it could be.

I'm also always looking for any other way possible to make the best of our pathetic equipment that we have at school. While I focus a lot on developing my talent, and the talent of the crew, I like to find new toys. I especially love any free audio program. (I tried TrueRTA, but it doesn't load on my home PC because of my dad's wacko administrator set up that never works...)

Anyways, thanks for the input and advice. Your soapboxes are my favorite part of this site, so keep them coming whenever.

I guess I'll probably just play around with listening some more, or maybe just try to work with a higher expert, who has actually heard in our auditorium. Maybe its not as bad as I think.


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## stantonsound (Jun 13, 2007)

I am sure that you have a favorite song, a song in which you know every beat and every note. It may not be something popular, just something that you listen to on your ipod or when you are alone driving in your car and can not help but to sing along. (For me....Wagon Wheel by Olde Crow Medicine Show, Paradise City by GNR, and Brr...Stick Em by Beastie Boys.)

Just pop the CD into the system and listen to it. It will sound pretty bad if the eq is off as far as you have said. Then play with the eq and make it sound better....and then a little better...and soon it will sound perfect. 

Different songs have different strengths, if you will. Some are high and mid, some are the low end. Go through a few songs and soon you will get something that you like. That is the easiest way to dial in a system. 

Also, if your speakers are biamp, it is possible that the crossover might be part of the problem, so take a quick look at that first.


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## Hughesie (Jul 4, 2007)

here's an idea, im currently working with it

it's a program called simple feedback trainer
the makers of the software, their site isn't always active so you can get a version of it off my website

www.alexhughes.bravehost.com then go to files and it is called simple feedback trainer

use that for a while, thought it might drive you crazy but it should help


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## SHARYNF (Jul 4, 2007)

Here is an oversimplified way to look at all this

You use an rta to alter the response of the speaker system independant of the room, to remove peaks and valley's and problems around the cross over points, you can use a geq or a dsp processor like say a BSS minidrive. 
.
You also can use an rta but typically just a trained ear and geq to eliminate feed back frequency problems in monitors. 

Room problems typically cannot be fixed by a rta/geq, and there is where you get all sorts of really wierd settings, where someone attempts to fix a room problem this way. The problem basically is that the rta only measures at a specific point, and cannot tell the difference from the originating sound and the reflected sound.
R
SO room problems are typically corrected by altering the position of the speakers and using reflection/deflection/absorption panels and materials.

The joke in the industry is what do I use to flatten a room... a bulldozer.
If you look at http://www.auralex.com/ it will give you an idea of what is done in small rooms.

Years ago people thought Rta/GEQ was going to fix all the problems until people started to actually study the problem. In most cases simply using a rta/and setting a geq based on a simple mic placement is not going to work

Sharyn


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## Schniapereli (Jul 5, 2007)

I already have that simple feedback trainer program, and have used it a little, but after a while it did get annoying. I am trying to get a computer at the school so I can use it there, and train other techies on it.
(and annoy them too)

I'll maybe look into getting panels. I'll ask a higher tech. If he thinks it's a big enough problem, then we might, but it's not a big issue.
It was one of those things on the bottom of the list, that would be worth it if it were easy. But, being a high school, we always have bigger problems that require our attention.

Thanks.


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## SHARYNF (Jul 5, 2007)

Can you describe the problems with the current system? If you can play a cd that you know and walk around and listen from various spots in the room, so you can hear problem areas etc

Sharyn


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## Schniapereli (Jul 6, 2007)

Things in there sometimes feel a little reverbery. But, the main thing is that I am told that we get strange feedback there. According to the other super-tech who comes in, strange frequencies get feedbacked. (I haven't worked in another theatre before, so I can't compare)

Also, when the audience comes in, everyone sounds squeakier, and we get more high frequency feedback. (I was told this is weird, but again, I don't know any better)

So, mainly, I don't really know what the problems are, because I don't know what a good sound system _can_ sound like, but others have told me that it is weird.
(that's why I'm so keen on having a computer tell me how to fix it)

That probably didn't help much. I might even be making this into a bigger deal than it actually is.


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## audioslavematt (Jul 6, 2007)

Schniapereli said:


> So, mainly, I don't really know what the problems are, because I don't know what a good sound system _can_ sound like, but others have told me that it is weird.
> (that's why I'm so keen on having a computer tell me how to fix it)



In that case, you're wasting your time. If you don't know what a tonally balanced system should sound like, leave it to somebody that does. If you don't know what to do with the results the computer gives you, it's pretty much guaranteed you'll do more harm than good.


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## SHARYNF (Jul 7, 2007)

You need a super tech with ears ;-)

Surely you have at some point in your life listened to a good stereo stereo system?

you should not hear the room, the points you are making sound like some combination of sound reflections, standing waves, etc, nothing that an rta is likely to fix. It might be useful to use the software with a mic and make lots of readings around the room and see how the readings vary.

Sharyn


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## Schniapereli (Jul 8, 2007)

I wish I had listened to a good stereo before, aside from a movie theater. I have never even been to a play outside of schools, or our very low quality local theatre. (I was looking forward to seeing Icewolf's Les Mis in his theatre close by, but I couldn't schedule it before they were sold out.)

I have never been to a concert before. All of my headphones, and personal stereos stink.

I once had the opportunity to go to the house of the guy who own Dolby Digital, but I had to miss it fr a stupid band thing.

I guess I really shouldn't be the one to try to EQ the whole sound system. 

I will definitely not touch it until aided with somebody who knows what they are doing.


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## Chris15 (Jul 9, 2007)

Hughesie89 said:


> here's an idea, im currently working with it
> 
> it's a program called simple feedback trainer
> the makers of the software, their site isn't always active so you can get a version of it off my website
> ...



Me thinks I might be looking at a breach of copyright... I'm about to go to bed so I haven't looked into whether open distribution is kosher in this case, but normally this would be naughty.


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## avkid (Jul 9, 2007)

Chris15 said:


> Me thinks I might be looking at a breach of copyright... I'm about to go to bed so I haven't looked into whether open distribution is kosher in this case, but normally this would be naughty.


Completely open licencing to my understanding.


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## not_me (Jul 10, 2007)

An RTA is a tool-
it's usually used to tune a system in a room, at one location
(wherever you put the measurement mic).
If you're having feedback problems,
it can guide you to what frequencies are building up in the 
room at the place that you're having problems.
Nothing wrong with using a MKEII and trying to 'flatten' it-
the limit's going to be the sound card anyway. 
Spend $200 for a better interface, things will get better.
Spend for a measurement mic, things will get even better.

The RTA's the current equivalent of a sharp rock in the trade,
but you can do a lot with a sharp rock.


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## museav (Jul 17, 2007)

A couple of points. Yes, the measurement microphone will affect the results and not just from the frequency response perspective, but also potentially from the polar and phase responses. For example, using a mic that is not perfectly omnidirectional at all frequencies could introduce non-linearities for any off-axis sounds.

Second, when making any measurements of system response you need to make them at several locations. Making things better at one location can make it worse at others.

Finally, measurement systems such as RTA, FFT, TDS, MLS or SIM are indeed just tools. They cannot tell you what sounds 'good' or 'right'. However, they can be very valuable in helping you see the problems, assesing what affect any changes made and determining what can or cannot be fixed via EQ. This last is where RTA systems have problems, they are indeed 'time blind' and display finite bandwidths so they are of limited use in assessing the causes of the problems and whether they can be addressed with EQ. Factors such as combfiltering, driver/speaker time alignment and room modes cannot be fixed with EQ and an RTA will not identify if what you are trying to fix is a basic frequency response issue or one of these issues than cannot be fixed with EQ.

RTAs are a great way to get some understanding of the relationships between frequency and sound and to identify gross problems such as feedback, but they will not keep you from spending hours trying to fix a problem that potentially cannot be addressed with EQ.


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## kesowul (Jul 24, 2007)

Unless you have the right tools to go about flattening a room, I wouldn't mess with it too much. Like everyone has said if you don't know what exactly you are doing, just use your ears. Theaters are usually reverberant reflective spaces which we try to mask with absorption (in the right places), time alignment, etc. Even if you have an RTA to see which frequencies are boosted or attenuated you're only looking at one spot. Most likely if you move just a foot or two away (if the room has bad reflections) you'll hear something totally different. You cannot help this with any amount of EQ because it has to do with the sound reflecting off of the different surfaces and reaching you at different times causing comb filtering. You have to find where and when the reflections in the room are happening from impulse responses. Have a specialist test the system SIM, SMAART, and TEF are great tools, but if you have no idea what to do with them they are no use. And when you do EQ a room try to use a parametric EQ instead of a graphic...what if you have a 1/3 octave GEQ with say 2.5K and 3.15K filters what happens when you get feedback at 2.8K? You might kill it by pulling down both of those sliders, but you are also killing a huge chunk of your frequency range.


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