The poor man's RTA

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bitflipper
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RE: The poor man's RTA 2009/06/19 17:58:45 (permalink)
And who knew THIS was possible:

TrueRTA Quick Sweep WITH Sound Card Calibration
post edited by bitflipper - 2009/06/19 18:09:41


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The Maillard Reaction
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RE: The poor man's RTA 2009/06/19 18:30:12 (permalink)
LOL


If you consider that you can use a mic with a calibration data sheet and the best converters you an afford it actually seems liker a bargain.

I think the next price point for that feature set is a bit of a jump after that.

FWIW I bought the $99 license several years ago and have been well pleased.

best regards,
mike


#62
Beagle
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RE: The poor man's RTA 2009/06/19 18:51:03 (permalink)
yes, no doubt - but you probably need to use it in a lot of different locations, right? I probably will only use this in my home and MAYBE another guy's house. hardly worth $100 for 2 uses!

for YOUR purpose it would be well worth the money, IMO, but not mine (and very likely not for MOST people reading this thread!)

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marcos69
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RE: The poor man's RTA 2009/06/20 00:22:28 (permalink)


I don't have an omnidirectional mic. Top pic is sm57 and bottom pic is AKG Perception 100 small diaphram. Am I screwed or can I use one of these?
post edited by marcos69 - 2009/06/20 00:42:31

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#64
The Maillard Reaction
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RE: The poor man's RTA 2009/06/20 07:43:47 (permalink)
Beagle,
You are correct, but bare in mind that I rarely suggest someone buy something.

I am frequently vocal about what I'd avoid buying. Its also sometimes obvious that I personally budget for expensive gear... but I'm not often seen recommending that others buy something.

When I selected TrueRTA for my needs I went to the trouble of spending 3 days demoing everything I cold find. True RTA has several price points and you can upgrade when you wish. I personally found it to be an honest value.

The $99 version seemed to work as well as the fancy gui $4,000 RTAs I looked into and it certainly outperforms a hardware RTA at many many times the cost.

I heartily recommend that one experience at least the free download version so as to provide an opportunity to see how it works... especially the actual calibration routines that provide for better consistency in your measurements.

best regards,
mike



post edited by mike_mccue - 2009/06/20 07:44:43


#65
Beagle
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RE: The poor man's RTA 2009/06/20 10:04:28 (permalink)
Mark - bitflipper or someone more experienced at this might be a better one to answer you, but I would *think* that the AKG would be a more accurate mic to use since it's a condensor and that's what bit recommended earlier in the thread.
ref:
To summarize the microphone considerations:
- Use the best condenser mic you have access to
- Use omni mode
- Switch off the pad
- Switch off the HP filter
- Bypass EQ and compression on the mic pre
- Position the mic at the mix position, at ear level

I would also think that NOT using an omni directional would not "screw you" but it will be BETTER results if you have an omni.

Mike: completely understandable and I respect your advice. I may try the free one anyone in addition to this test that bit has given us. thanks for the suggestion.
post edited by Beagle - 2009/06/20 10:11:43

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Beagle
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RE: The poor man's RTA 2009/06/20 10:09:56 (permalink)
Ok - I've finished 1/2 of my bass traps, so I'm not quite ready to install everything and run the "AFTER" test. but here's my BEFORE test:



so if I'm reading it correctly, it looks like I need some absorption between 100Hz and 500Hz, but mostly at about 110Hz to 130Hz.

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#67
The Maillard Reaction
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RE: The poor man's RTA 2009/06/20 10:26:34 (permalink)
Yes and no... adding bass absorption will likely also boost the drop off below 100 and help flatten it out as the hump you are speaking off comes down.

The drop off below 100 is probably a combination low output from your speakers and nulling from room flutter.

Controlling the flutter will, probably, enhance the character of the bass that is coming out of your speakers.

Have you tried running Span at higher res? a.k.a Block size?

Even at full res it's hard to get satisfactory detail in the low frequency measurements.

I think if you switch to hi res block and keep a fast response you'll see there is a lot of fluttering going on down there.

Then as you add bass absorption you'll notice the fluttering subside.

best regards,
mike


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Beagle
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RE: The poor man's RTA 2009/06/20 11:16:04 (permalink)
Increasing the block size yields this:



which shows higher activity at 50Hz and below.

but if I increase the SPEED, regardless of the block size, I see a lot of "fluttering" activity below 500Hz - mainly in the 100Hz and below area and most of the fluttering is 3dB-6dB in variation.

Ok - now here's the real question. I said I haven't finished building ALL of the traps I plan to put in my room, but I have finished FOUR of them. they are 2'x4'x6" with 2" 703 covered in burlap. I see a difference in the test before and after putting these 4 traps in, but it seems to have INCREASED in areas.

My room is strange - it's actually a formal dining room. I have one large 6' wide opening at the back of the room, the width is approximately 10' and the length is approximately 14' and it's 8' tall (with a vaulted ceiling and a skylight).

I have 3 of them in front of me (behind the speakers) and one in the rear of the room. I know it is probably more optimal to put more in the rear of the room, but it's also more difficult because of the large opening. the other 3 units will be going in the rear of the room. I didn't expect dramatic improvement with only these 4 units and the way they're positioned, but I did expect SOME.

with the settings back to the original, here's the test with the 4 units in the room:



and here's the original before the 4 traps:



it's actually INCREASED between 200-300Hz and there's now a spike at the 3kHz. what have I done wrong?
post edited by Beagle - 2009/06/20 11:18:31

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#69
Dave King
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RE: The poor man's RTA 2009/06/20 12:02:07 (permalink)
Check your db scale settings. To compare apples to apples with bit's results, it should be: -20 130

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#70
The Maillard Reaction
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RE: The poor man's RTA 2009/06/20 12:03:32 (permalink)
You haven't moved the traps around enough... just keep moving them and observing.

Your results are predictable... by settling the nulls the "apparent" bass has become more defined and measurable.

And PLEASE PLEASE PLEASE start running the SPAN at a higher res so you can actually see what's going on down in the lows.

best,
mike


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bitflipper
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RE: The poor man's RTA 2009/06/20 12:13:45 (permalink)
Beagle's right, Mark. Use the condenser. It'll have a much flatter response than the 57 and although it's also cardioid it's pattern is not as narrow as the 57. Condensers also tend to have smoother off-axis response than dynamics, which is important in this scenario.


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

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#72
marcos69
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RE: The poor man's RTA 2009/06/20 12:19:33 (permalink)

ORIGINAL: bitflipper

Beagle's right, Mark. Use the condenser. It'll have a much flatter response than the 57 and although it's also cardioid it's pattern is not as narrow as the 57. Condensers also tend to have smoother off-axis response than dynamics, which is important in this scenario.


Thanks!

Mark Wessels

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#73
bitflipper
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RE: The poor man's RTA 2009/06/20 12:28:30 (permalink)
it's actually INCREASED between 200-300Hz and there's now a spike at the 3kHz. what have I done wrong?


Yes, some frequencies will increase when you trap them! Room resonances don't just cause peaks, they also cause nulls and partial nulls. Dampening resonances will lower some frequencies and raise others - the goal is an overall flattening.

Your screenshots suggest that your traps are not effective in the 100-200Hz range, which is not surprising. To be effective in that lower range, the traps have to be really thick, placed and spaced just right. You might start thinking about a Helmholtz resonator tuned to 150Hz.

You're going to have unavoidable inconsistencies between measurements. They will be most obvious at the higher end of the scale, where shorter wavelengths mean that moving the mic just an inch or two will result in different levels. The increase at about 15KHz can probably be so explained (the wavelength at 15KHz is less than an inch).



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

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#74
Beagle
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RE: The poor man's RTA 2009/06/20 12:33:01 (permalink)
ORIGINAL: mike_mccue

You haven't moved the traps around enough... just keep moving them and observing.

Your results are predictable... by settling the nulls the "apparent" bass has become more defined and measurable.

And PLEASE PLEASE PLEASE start running the SPAN at a higher res so you can actually see what's going on down in the lows.

best,
mike

Oh - ok. I'll move them around and keep running tests (after I've finished the other traps, actually). I've set the block size to maximum, now and left it there.

Dave King - I did change it, but I didn't think that mattered according to what bit said earlier.


I'll post some more when I find a good fit of moving them around, but I think if that's the case I'll wait until I get them all done since moving 4 around will be a different scenerio than moving 7 around.

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Beagle
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RE: The poor man's RTA 2009/06/20 12:37:31 (permalink)
ORIGINAL: bitflipper

it's actually INCREASED between 200-300Hz and there's now a spike at the 3kHz. what have I done wrong?


Yes, some frequencies will increase when you trap them! Room resonances don't just cause peaks, they also cause nulls and partial nulls. Dampening resonances will lower some frequencies and raise others - the goal is an overall flattening.

Your screenshots suggest that your traps are not effective in the 100-200Hz range, which is not surprising. To be effective in that lower range, the traps have to be really thick, placed and spaced just right. You might start thinking about a Helmholtz resonator tuned to 150Hz.

hmm. ok - I've heard of them before but haven't researched them. I'll look into that.

You're going to have unavoidable inconsistencies between measurements. They will be most obvious at the higher end of the scale, where shorter wavelengths mean that moving the mic just an inch or two will result in different levels. The increase at about 15KHz can probably be so explained (the wavelength at 15KHz is less than an inch).

yeah - i'm aware of that - I'm an EE - although I'm sure many people reading this need to know it as well.

thanks, dave.

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#76
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RE: The poor man's RTA 2009/06/21 12:03:25 (permalink)
Thought some folks here might enjoy this:

http://www.sonicvisualiser.org/
post edited by forumuser - 2009/06/21 12:14:53
#77
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RE: The poor man's RTA 2009/06/21 14:00:23 (permalink)
ok, thanks, but what does it have to do with analyzing your room?

the description for this software you linked to says this:
Sonic Visualiser is an application for viewing and analysing the contents of music audio files.


so I don't know how that applies to analyzing the room.

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RE: The poor man's RTA 2009/07/19 16:24:06 (permalink)


Ok, here is my analysis after room treatment. How does it look? I used 4" of Owen's 705 for corner bass traps and 2" 703 on the walls for reflections.

post edited by marcos69 - 2009/07/19 17:00:07

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Dave King
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RE: The poor man's RTA 2009/07/19 17:32:19 (permalink)
I;m no expert, but I think it looks pretty good. bit?

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bitflipper
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RE: The poor man's RTA 2009/07/19 21:16:45 (permalink)
Yeh, if you can get it down to about a 6db variance, you're doing as well as most professionally-treated rooms.


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

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marcos69
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RE: The poor man's RTA 2009/07/19 21:48:50 (permalink)
My first impressions on using the room now, I get bass in the listening position. I never had bass before, I would have to sit against the back wall to hear any. I also hear highs that I never heard. I wonder what effect the room rolling off over 10k will have on me though.

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Dave King
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RE: The poor man's RTA 2009/07/19 21:54:28 (permalink)
My first impressions on using the room now, I get bass in the listening position. I never had bass before, I would have to sit against the back wall to hear any. I also hear highs that I never heard. I wonder what effect the room rolling off over 10k will have on me though.


When I installed my room treatment, I didn't notice much difference in the low freqs specifically, but I did notice that everything sounded much more focused.

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#83
bitflipper
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RE: The poor man's RTA 2009/07/19 22:09:48 (permalink)
I wonder what effect the room rolling off over 10k will have on me though.

That's the downside of all that absorption. Two things you have to be careful of after you've added a lot of absorption: overcompensating the high frequencies over 10KHz, and using too much reverb in your mixes.


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

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marcos69
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RE: The poor man's RTA 2009/07/19 23:17:14 (permalink)

ORIGINAL: bitflipper

I wonder what effect the room rolling off over 10k will have on me though.

That's the downside of all that absorption. Two things you have to be careful of after you've added a lot of absorption: overcompensating the high frequencies over 10KHz, and using too much reverb in your mixes.


Yeah, the room is essentially dead now. I'll have to really watch the reverb.

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craigt
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Re: RE: The poor man's RTA 2009/07/22 14:48:30 (permalink)
For some reason SPAN does not freeze when I click the echo button to turn it off (using S8PE).  I believe I am using all of bit's settings.  Any suggestions?
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bitflipper
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Re: RE: The poor man's RTA 2009/07/22 15:01:29 (permalink)
No idea. Do you have "Peak Hold" set to "Infinite"?


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

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Re: RE: The poor man's RTA 2009/07/22 15:14:45 (permalink)
Thanks bit, I hoped you would think of somthing I might have missed.  I'll check when I get home this evening.
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Re: RE: The poor man's RTA 2009/07/22 15:40:11 (permalink)
You could do a screen capture.  Alt+Prc Scr and paste into image editor.

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Re: RE: The poor man's RTA 2009/11/11 11:37:36 (permalink)
This deserves a bump as it's so cool.  I'll be testing tonight or tomorrow.  Can't wait to see them!

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