The poor man's RTA

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batsbrew
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RE: The poor man's RTA 2008/09/29 16:30:16 (permalink)
so, 2 questions:

if i have a space that i cannot aggressively treat, is the answer a 31 band eq, and eq for the flattest sound possible in whatever environment you happen to be in?

or is it to simply know where the bumps/valleys are, and eq (in the head) accordingly?


i did this for years, in a live sound reinforcment situation...
where the rooms constantly changed, and the equipment did not....

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#31
bitflipper
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RE: The poor man's RTA 2008/09/29 19:29:55 (permalink)
It is possible to smooth out some anomalies using equalization, despite popular opinion to the contrary. That's the principle behind "room correcting" monitors and the IK Multimedia ARC system.

Yes, it's essentially the same concept as the time-tested method of pairing a realtime analyzer with a 31-band graphic equalizer for setting up PA systems. I did that for years, too. But if you've done that you also know that it's still hit-and-miss, and the room's characteristics will always change drastically once it fills with sound-absorbing human bodies, requiring further tweaks as the night wears on.

Equalization cannot address nulls, however. If you cannot install bass traps the only workaround is to identify where they are and try to avoid compensating for them when you EQ your music.

I recently did an experiment wherein I applied a (software) parametric equalizer and adjusted it based on my readings from Ethan Winer's stepped sine test. There was a measurable and audible improvement. However, the worst anomaly in my room's frequency response could not be helped, as it was caused by a null at the mix position.




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#32
bitflipper
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RE: The poor man's RTA 2008/09/29 19:38:48 (permalink)
What happens if there is a mosquito in the room? Do I need to change things to compensate?
What if it's humid, or if I am wearing cotten instead of nylon?
I don't think I am ready for this level of detail.


No, mosquitos can be ignored. Sonically, at least.

Cotton versus nylon might have more effect than you realize. Simple things like wearing a hat will affect your perception of certain frequencies. It definitely makes a difference how many people are in the room with you.

But these are fairly minor influences. As long as you always sit in the same position, and don't invite a crowd over for your sessions, you'll do all right.

What we're talking about here are much more dramatic than mosquitos and hats. We're talking about 20 or 30db fluctuations in perceived levels. That's huge. Imagine someone trying to sell you a set of speakers whose frequency response was followed by "plus or minus 30db". No way you'd buy such a crappy product. But that's exactly what an untreated room does to your expensive calibrated kevlar/molybdenum/kryptonite reference monitors!


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#33
alxi
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RE: The poor man's RTA 2009/01/14 13:46:24 (permalink)
Thanks BF... very usefull.... I have tried with 2 different mic and i have played with the eq settings on my speakers ( hs-50 ) i am now more confident about what i ear. Surprinsingly enough, i had a pretty good response... a bit too much absorbtion in the highs so i know i have to go easy in that area.

Could this technique be use to mesure SPL ??

thanks

-Alxi-
post edited by alxi - 2009/01/14 13:50:58

For ever learning
#34
The Maillard Reaction
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RE: The poor man's RTA 2009/01/14 14:07:16 (permalink)
It's true, I wear straw for country and felt for western.


#35
jacktheexcynic
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RE: The poor man's RTA 2009/01/14 19:51:34 (permalink)
thanks bit! this thread went in my list of must-keep threads...

- jack the ex-cynic
#36
The Maillard Reaction
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RE: The poor man's RTA 2009/01/14 19:59:28 (permalink)
Bit, isn't a resonant peak just a negative null?

Doesn't the EQ just allow you to reduce the source so as not to excite some portion of the spectrum into resonance?



#37
bitflipper
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RE: The poor man's RTA 2009/01/14 22:24:46 (permalink)
Bit, isn't a resonant peak just a negative null?


That's one way to describe it, although technically "null" only applies when reflections are 180 degrees out of phase with the source. But yes, peaks are caused by the same physical phenomenon as nulls. And yes, dampening reflections with absorbers helps with both peaks and nulls, which is why you always try to treat anomalies acoustically before resorting to equalization.

From a practical standpoint, peaks differ from nulls in that peaks can be mitigated through equalization *, whereas nulls really can't. However, every peak has an accompanying null at a different location in the room, so if you lower a frequency that has a nasty peak at the listening position, you will also have a positive effect on a null somewhere else.

I have recently added electronic equalization in my quest for sonic nirvana. I've just about put up as much 703 as the room can accommodate, but an annoying peak at 142Hz remains at the listening position. It corresponds to half the wavelength of the room, and is the result of my chair being dead center in the room (necessary to get the speakers away from walls). The EQ has worked out quite well, and I am really enjoying listening to my reference CDs, which sound better than ever.

EDIT:
* I should point out that reducing peaks through EQ can only be done at the listening position. Any EQ you apply will almost certainly fark up the sound somewhere else in the room. However, if your intent is a flat response at that one location, equalization can be immensely effective. My monitors sound absolutely gorgeous right now - but only in the mix chair.
post edited by bitflipper - 2009/01/14 22:42:34


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#38
bitflipper
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RE: The poor man's RTA 2009/01/14 22:32:57 (permalink)
Could this technique be use to mesure SPL ??


No. At least, not with any accuracy. Your best bet is to purchase an inexpensive SPL meter, which can be had at Radio Shack for about 30 bucks. Every studio should have one, since you always want to make measurements and calibrate your system at the same SPL.

When I test my room, I always set the speaker at 85db SPL with the (omni) microphone as close to where my head normally resides when mixing. I probably should use a lower volume, closer to the level I normally mix at, but I used 85 as the standard when I first started doing this (based on Bob Katz's method) so I stick with 85 so that current measurements can be related to older measurements.


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#39
alxi
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RE: The poor man's RTA 2009/01/14 22:39:24 (permalink)
Allright Thanks again... Tomorrow... RS here i come :)

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#40
Dave King
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RE: The poor man's RTA 2009/01/15 17:31:52 (permalink)
Very interesting test. I'll have to give it a whirl this weekend.

Thanks bit!

Dave King
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#41
The Maillard Reaction
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RE: The poor man's RTA 2009/01/15 18:58:28 (permalink)
Thanks for elaborating Bit. Great food for thought.

Dave, love the new avatar.

best,
mike


#42
jimmyman
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RE: The poor man's RTA 2009/01/15 20:19:01 (permalink)

bitflipper

you have covered such an emmence range of talk about
RTA

analize the room
eq the system or not
methodes to analize

all "normal" rooms or bedroom type dementions will get
all exited at about 160 hz (in my case)

if the singer is singing an "a" note for example and the room
exites at 160 hz (whatever frequency that is) then you know
what happens,

the songs "key" can sound better in one room as oppsed to
another. my room is damped out the ying yang.

even "traps" reflect sound go figure?

I conlude to say that test and "room" treament are both
nesasary

"test are a good thing" so ill add this.

take a sine wav and and play it from 20 to 20,000 hz in
5 seconds. using the radio shack meter.

youll see little flutuation in level at any given freqeuncy.
do this with 10 seconds or 30 seconds or two minutes.

the more time you analize it the worse it gets. why?
its the truth.

its physics

How can a song sound so good even on a 3" speaker?
Im sure of this! they knew what RTA was!

jimmy

#43
Dave King
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RE: The poor man's RTA 2009/01/19 15:05:54 (permalink)
I was curious about this test especially since I put in some acoustic treatment in my studio space last fall.

I did the test according to bit's directions and even used a KSM44 in omni mode (as he did).

Here is my results:



How does it look?


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#44
Dave King
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RE: The poor man's RTA 2009/01/19 15:14:18 (permalink)
On closer inspection, I realized I was not using the same settings in SPAN as bit used. So, I ran the test again:



Those db Scale sttings do make a difference.

Dave King
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#45
Storm
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RE: The poor man's RTA 2009/01/19 15:55:28 (permalink)
sticky
#46
bitflipper
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RE: The poor man's RTA 2009/01/19 16:52:38 (permalink)
That's actually quite a good graph, Dave. Better than I've been able to achieve.

I, too have that rolloff above 8KHz, which I believe is the price of using absorbers to tame low frequencies. It's one of the reasons some people get the 703/705 with the paper backing and leave the paper on facing outward, to reduce the absorption at the high end.

This goes to show why acoustics are a) so important and b) so frustrating. That theoretical flat line we'd like to see is actually unattainable. A really good response is still plus or minus 5db. According to one acoustics reference book I read, the very best studios with million-dollar treatments are within 5db.

Just imagine if you bought a microphone with a 5db peak in its frequency response. You'd call it a cheap mic. Or a set of speakers that were only flat plus or minus 5db. You'd call those...oh I won't name names, but they're on display at your local GC if you're curious.

We spend big bucks on quality gear only to discover that the room is making our expensive amplifiers, speakers and microphones all sound like generic junk. Anybody who goes out and buys $2000 speakers - like I did - without first seriously addressing acoustics - like I didn't - is throwing money away.

EDIT:
By the way, here's the hot tip: Behringer FPQ2496.

I thought I was being clever, adapting this box to suppress resonant peaks in the mix position, since Behringer does not promote it for that purpose. But it turns out the home theater crowd has been using this unit's predecessor for years to tune subwoofers, and the excellent free acoustics software Room EQ Wizard supports it directly.

This little box features 40 (!) parametric filters (20 per side) that can be set with extremely high or extremely low Q values. You put it in line with your monitors so it has no direct effect on your mixes and zero CPU overhead like you'd incur with software-based correction.

And the best part is that it's cheap. $150 through most vendors, but I found one for $116 including shipping.

Just don't be tempted to try and make your room totally flat using an equalizer. It won't happen. Also, use only cuts, and either avoid boosts altogether or only use very gentle boosts with wide bandwidths. And keep in mind that room EQ only works in one spot, and the better you make it sound at that spot the worse it will sound in other parts of the room.

Note that many sources complain about the Behringer's noise floor. Most of those complaints refer to the earlier, less-expensive 46KHz version. The FBQ2496 does not have noise issues that I can discern.
post edited by bitflipper - 2009/01/19 17:17:20


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#47
jayhill
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RE: The poor man's RTA 2009/01/20 20:33:56 (permalink)

ORIGINAL: bitflipper

VOXENGO SPAN

The following SPAN settings are chosen to best emulate a hardware RTA.
- Slope: 0.0db (!)
- Monitor: RealT, Instant, 1/3
Of these, all are default settings except for the slope and the 1/3 octave display mode



Yikes! I can't believe I went thru this whole procedure a year ago and forgot about the slope On Voxengo SPAN.

Ok - start over.
#48
lackluster strumming
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RE: The poor man's RTA 2009/01/20 23:40:45 (permalink)
I hear that a lot of the guys in nashville use the beringer reference mic for this. they go through a lot of them and supposedly these are pretty good bang for the buck. I don't know which model but i do know it's 50 dollars.
#49
bitflipper
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RE: The poor man's RTA 2009/01/21 11:22:03 (permalink)
Yes, the ECM8000 is a good deal for fifty bucks. However, for this kind of measurement having a calibrated microphone really isn't necessary. Any quality condenser will do, because any variations in the mic's response curve are going to be trivial compared to the wild variations in your room's response.


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#50
batsbrew
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RE: The poor man's RTA 2009/05/19 11:40:31 (permalink)
bump worthy

Bats Brew music Streaming
Bats Brew albums:
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"Stay"
"The Time is Magic"
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#51
DW_Mike
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RE: The poor man's RTA 2009/05/19 12:00:47 (permalink)
I was wondering about mic placement. I use the ECM8000 for this. I place the mic at my mixing position but which way should it face, straight up and down pointing toward the ceiling or should I point it the same way that I look while sitting there, between the monitors toward the PC screen?
Does it matter?

Mike

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#52
Dave King
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RE: The poor man's RTA 2009/05/19 20:55:15 (permalink)
Point it forward towards the monitors (same direction as your ears).

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#53
DW_Mike
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RE: The poor man's RTA 2009/05/19 21:37:41 (permalink)
Thanks Dave. I've always wondered about that.
I'll have a run with it pointed the right way this time.

Mike
post edited by chefmike8888 - 2009/05/19 21:47:24

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#54
rstollen
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RE: The poor man's RTA 2009/05/20 01:03:39 (permalink)
Thanks batsbrew for bumping this - definitely worth reading again.

To bitflipper - I think cakewalk ought to recognize especially helpful forum members (maybe once a year), and it should be named after you as the first winner.

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Beagle
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RE: The poor man's RTA 2009/06/19 13:02:44 (permalink)
I plan on trying this tonite! I've been building bass traps and they're not quite finished yet, but I need to do a before/after picture of the room and Dave (bitflipper) has given such a clear and concise set of directions! thanks again, dave, you da man!

I also picked up an ECM8000 because I didn't have an omni condensor anyway, only cardioids.

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#56
marcos69
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RE: The poor man's RTA 2009/06/19 14:13:45 (permalink)
Thanks Reece for the bump too. I'm addressing my acoustics right now and timing couldn't be better. Thanks BF for this info.

Mark Wessels

At CD Baby

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#57
The Maillard Reaction
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RE: The poor man's RTA 2009/06/19 14:38:41 (permalink)
here's a suggestion:



#58
Beagle
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RE: The poor man's RTA 2009/06/19 15:27:22 (permalink)
http://www.trueaudio.com/index.htm

yeah, but the free version is only 1 octave! you have to pay for higher resolution!
1 Octave FREE!
1/3 Octave $39.95
1/6 Octave $69.95
1/24 Octave $99.95

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#59
bitflipper
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RE: The poor man's RTA 2009/06/19 17:47:41 (permalink)
But it does go to 50KHz! How else are you going use those Earthworks microphones?

The TrueRTA actually looks pretty cool, but at a hundred bucks isn't exactly a "poor man's" RTA.

Still, it's less than I paid for my hardware version which is only 1/3 octave.


All else is in doubt, so this is the truth I cling to. 

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#60
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