Supersimple superficial room check - a waste of time?

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Kalle Rantaaho
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2012/03/29 08:02:59 (permalink)

Supersimple superficial room check - a waste of time?

Just popped in my mind.
Would it be ridicilous to record white noise (was it white or red or green that is used for this purpose ??) from my monitors and record it with Zoom2 and analyze the frequency curve in order to do some EQing at E-MUs output.
 
The mics of Zoom are not that bad, but how good do you need to get results that make any sense.

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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 08:23:56 (permalink)

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    ChuckC
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 08:24:32 (permalink)
    Sounds like you are looking for something along the lines Of the ARC system, or the KRK Ergo to help correct deficiencies in you room.    

    ADK built DAW, W7, X3 Producer, Studio One Pro,Yamaha HS8's & HS8S  Presonus Studio/Live 24.4.2, Saffire pro 40,  Ada 8000, Art TPS II, etc.....
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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 08:32:28 (permalink)

    Hi Chuck why not just start with a RTA, or Real Time Analyzer?

    "Correcting" makes for a good 2nd or 3rd step.

    A RTA will give you chance to simply observe and consider what is happening.

    I find them fascinating, as you can literally observe the difference in response at the sample position when you do things like move a couch, or place a bass trap, or adjust a diffuser panel.

    It's fun, and sometimes you learn a few things too.


    I recommenced http://www.trueaudio.com/ as a source for a nice easy to use RTA. It is about as accurate as any can be on a PC based audio I/O measuring system. I use the full package and enjoy it.


    all the best,
    mike


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    Danny Danzi
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 08:45:04 (permalink)
    mike_mccue


    Hi Chuck why not just start with a RTA, or Real Time Analyzer?

    "Correcting" makes for a good 2nd or 3rd step.

    A RTA will give you chance to simply observe and consider what is happening.

    I find them fascinating, as you can literally observe the difference in response at the sample position when you do things like move a couch, or place a bass trap, or adjust a diffuser panel.

    It's fun, and sometimes you learn a few things too.


    I recommenced http://www.trueaudio.com/ as a source for a nice easy to use RTA. It is about as accurate as any can be on a PC based audio I/O measuring system. I use the full package and enjoy it.


    all the best,
    mike

    Hey Mike, I'm curious about this....how would you perform a correction using this method and make it accurate? Like...wouldn't you need some special kind of mic that wouldn't color the sound or be too sensitive? Even the pre-amp chosen...could it somehow mess up your final results?
     
    Like...for example, if someone used the the method you put up and had a Royer or something...and then did the same correction using a Nuemann, wouldn't the results be different? And...if so, which ones do you use/trust? What mic would you use for something like this?
     
    I've had that software for quite a long time and always wanted to try my own correction. My biggest fear was possibly not doing it correctly and wasting time of course...and which mic would I choose? The other reason I wanted to try it, was to see how close ARC was to this. But in thinking about it further at the time, ARC does a bunch of correction spots, not just one...so it would probably be impossible to compare them, right? Uggh...this is the stuff I wish I had a bit more intelligence on.
     
    -Danny
    post edited by Danny Danzi - 2012/03/29 08:46:33
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    Karyn
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 09:02:04 (permalink)
    Danny,  all room correction/measuring devices work the same.  You put out either pink noise or a frequency sweep and display the result with reference to the frequency responce of the sampling mic.

    As long as you know the true response of your mic it doesn't matter what it is.

    Mekashi Futo.
    Current DAW.  i7-950, Gigabyte EX58-UD5, 12Gb RAM, 120Gb SSD, 2x2Tb HDD, nVidia GTX 260, Antec 1000W psu, Win7 64bit, FireStudio 2626, Digimax FS, KRK RP8G2,  X3e-Producer 

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    Danny Danzi
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 09:15:53 (permalink)
    Hi Karyn, thanks for that. But wouldn't you get different results if you did the correction with one mic and then did the correction with another? Or do you just not use a mic due to its frequency response? This is sort of where I get lost.

    Like for example...and maybe this has nothing to do with anything...lol....but let's say you had a cracked version of ARC and you didn't have the mic they supply. If you used one of your mic's with it, it wouldn't correct right. I've tried it and let me tell ya...it's horrible unless I use that mic they give me. LOL! Behringer has a little mic that has the same response curve as the ARC mic...but for some reason, that too fails miserably.

    I guess my thing is...if a mic picks up that pink noise and gives you a curve that may not be correct and you don't know this at the time, wouldn't you be making a mistake in trusting it? I'm probably not explaining this very well...I'm sorry. I just don't see how you could use any mic since each one is going to respond differently, won't they? If you can use any mic...how exactly do you compensate for this? Look up the frequency of that mic and factor that in or something? Thanks!

    -Danny
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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 09:30:41 (permalink)

    Hi Danny, FWIW I sent my mic to a calibration facility and had it returned with a file that TrueRTA uses internally to compensate for the mic's unique response. In all honesty, I don't use this RTA to make absolute measurements, I use it to observe changes.

    The easiest to observe is the way the bass activity calms down when I pile the bass traps in the corners or pull the speakers away from the walls.

    You can also see how diffusion comes in to play when you use it to tame erratic peaking in the upper mid band.

    Like I say, I just use it to observe and learn.


    If for example; I ever did use the ARC system, I would feel the urge to run the RTA on top of the ARC system just so that I may observe how good a job ARC is doing.


    all the best,
    mike

    post edited by mike_mccue - 2012/03/29 09:32:35

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    Danny Danzi
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 09:33:58 (permalink)
    Ok, thanks for the reply Mike. See this is what I'm talking about....see how you had your mic calibrated? If someone didn't have that done and just threw up any old mic, chances are, they may not have accurate results...correct? I'm just trying to find out how accurate or inaccurate just tossing up any mic would be. I'll get an education on this stuff yet I tell ya! :) Thanks!

    -Danny
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    Karyn
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 09:48:19 (permalink)
    It's all down to the response of the mic.

    ARC will have the response curve of their custom mic pre-programmed into the software. If you use a different mic it won't work as expected.

    As you know, the reason that multi-thousand dollar LDC mics sound beautifull on vox and accoustic guitars is because of the subtle lifts in the high mids of their response which complement the human voice.  The same for the good ol' SM57.

    Cheap chinese LDCs tend to have a flat(er) response and sound "dull" because of it.

    But, for room correction, all you're interested in is knowing the actual response.  Pink noise contains all frequencies at equal volume (as opposed to white noise which is high end biased).  You set up your mic at your listening position (nowhere else matters) and adjust the EQ of your playback amp untill the graph on the screen matches the response graph of the mic you're using.

    If you change mics, you need to know the resonse graph for that mic.


    In this case, the cheap chinese mics are actually a good choice, being "flat" to start with.

    I should also point out that you must use an omni pattern mic, so an SM57 is out of the question...


    The only thing that ARC does is adjust the EQ automagically.  You get exactly the same effect using "Span" and a good EQ plug.


    With regard to the EQ, it must be on your speaker output ONLY. You don't want all your masters coloured with your room correction EQ.
    The best way is obviously and external hardware EQ before your amp/powered speakers.
    Failing that (and what I do), create two stereo busses called "Phones" and "Speakers". Route them to the respective outputs of your sound card.  On the normal "Master" buss, create two post-fade sends that go to the Phones bus and Speaker bus. Put the room EQ on the speaker bus.

    This lets you EQ the speakers without affecting your master, and you can monitor on headphones without hearing the room EQ, and you can play with the phones or speaker volumes on screen without affecting the Master.   You could even set up a seperate EQ on the phones channel to correct them....

    Mekashi Futo.
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    Danny Danzi
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 10:01:49 (permalink)
    Gotcha...I got it now. Thanks for the detailed response Karyn. :)

    -Danny
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    SCorey
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 10:48:16 (permalink)
    That's one of the things that I've never seen adequately explained about ARC. You choose between two models of mic and run your analysis. But you don't choose a specific serial number of a mic so I doubt that ARC knows the exact response of the particular mic you got in your ARC package. It doesn't inspire much confidence in me.

    -Steve Corey
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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 11:05:10 (permalink)
    Hi Danny,
     I'd like to point out 2 things to think about.

    1) My mic went to a certified facility with an anechoic chamber that certifies forensic mics for use in laboratories and criminal court and came back with a highly detailed database that describes the response, but as I say, we don't need that info just to observe changes, we only need that info to measure absolute levels. I sent it off because it was easy to do.

    2) Here's an obvious question; Where does IK Multimedia have the mics that are included with ARC calibrated*?

    2a) Is there some place within the ARC app where I load the calibration correction info as unique to the exact microphone supplied by IK?

    2b) Is there a way to use some other mic, maybe an official IK replacement, that has a different and unique calibration correction file? Is there a place in ARC where I load in the specific mic's calibration correction information?

    Questions 2a and 2b are ideas I've always wondered when I read the description of the "calibrated* mic" in the ARC literature.




    I recall a story told by David Bock of his visit to a manufacturing plant in China that makes microphones for lots of big name vendors. He saw a table where employees sat and hand drew response curves on official mic calibration sheets. They drew just what the vendor ordered in nice fresh ink so it looked like each one was unique and then placed a sheet in the box with each mic they sold. It so happened that they didn't actually test the mics... they just drew in the intended response and said they did.


    Have you ever asked IK Multimedia what their calibration process is? Maybe you already know all these answers. I haven't used ARC so I have wondered about it.

    A) I'd ask if the mic response testing is done in an anechoic chamber.

    B) Mics can only be certified for short periods of time and then require re certification. I'd ask if the calibration process used by IK is capable of providing info that meets certification standards so that the mic may be found to perform as described if/when tested in yet another anechoic chamber within the specified time range. In other words, is the testing detailed and uniformly accurate or is the test simplified in some way?

    C) I'd ask to confirm if the IK certification process results in a "calibration correction file" that is specifically and uniquely applied withing the ARC application to "calibrate*" the specific mic's measured output, or if the term "calibrated*" is some sort of misnomer employed by IK Multimedia to make the accuracy of the ARC system seem impressive.


    *calibrate(d): It's important to note that you can not calibrate a microphone. You can only calibrate the output of a microphone by using the information supplied in the calibration correction file with a application that performs the correction. The point is, the application has to specifically apply the correction by using unique information associated with a particular mic, or it can just sort of generically calibrate the mics output with generic correction information.



     best regards,
    mike



    edited some spelling and grammar
    post edited by mike_mccue - 2012/03/29 12:31:00

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    SCorey
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 11:17:13 (permalink)
    Exactly, Mike. That's what I was trying to get at.
     
    Cheap chinese "calibration" mics are anything but flat, unless you get lucky. http://www.cross-spectrum.com/weblog/2009/07/ Be sure to check out the bottom of the page, the "Update, April 5, 2010" section. That page also links to a German site with the same sort of info, but with a broader range of mics.
     
    IK tells you nothing about how flat their mics actually are, or what sort of calibration they use and how they deal with the consistency problem. What's their QC tolerance? How many mics to they reject before getting one that is ARC "worthy"? Do they reject any at all? Maybe that's why I don't like ARC--maybe I got a bad mic. I have it, I've tried it (including taking probably hundreds of measurements), I don't use it.
     
     
    post edited by SCorey - 2012/03/29 11:23:29

    -Steve Corey
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    drewfx1
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 11:32:16 (permalink)
    I guess the question that should be asked is:

    How much does the response differ in a reasonably flat uncalibrated (omni) mic vs. differences in the room?

    [EDIT: Here's some testing from Ethan Winer's Realtraps site that compares cheap and expensive "measurement" mics: http://www.realtraps.com/art_microphones.htm. Note from the graphs at the bottom how the differences between mics compares to the low frequency response differences in the room]


    And if you move the mic around, including close to the speaker, the room response will change to varying degrees, but the mic's response will stay the same.
    post edited by drewfx1 - 2012/03/29 12:21:21

      "The original X1"
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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 15:57:04 (permalink)

    Hi Corey,
     The link you posted to has this rather revealing graph of the measured response of 85 presumably identical mics.

     

     My guess is that IK Multimedia gets their mics from the very same place that Behringer and DBX does.

     This illustrates why it is sort of preferred to use an actual and specific correction file when attempting to make absolute measurements. Apparently ARC just fudges a few things here, yet still offers good benefits to many users who aren't worrying about that sort of accuracy. Personally I'm not worried about that kind of accuracy. I wonder how many people who are interested in the accuracy of the readout of their RTA or room correction system know how that works?


     Hi Drew,
     The link you posted to shows that if you are mainly interested in observing difference after some change that just about any mic will do and prove to be very helpful As long as you don't pretend to have actually measured an absolute value you can get plenty of good work done with just about any good omni mic. (hint, don't mistake a figure 8 for an omni)

     


    I posted the synopsis just in case the actual articles seemed to tedious for people interested.


    all the best,
    mike

    post edited by mike_mccue - 2012/03/29 15:58:25

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    bitflipper
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 16:17:04 (permalink)
    I guess the question that should be asked is: How much does the response differ in a reasonably flat uncalibrated (omni) mic vs. differences in the room?

    Thank you, Drew! Allow me to amplify...


    When we're talking about room resonances and other acoustical distortions, the frequency response of the microphone is almost irrelevant. Keep in mind that variations in the room can be 30 decibels or more. The crappiest Radio Shack microphone is far flatter than that.


    To answer the original question: yes, you can glean useful information from such a test. While you're doing it, take snapshots at different microphone positions around the mix position and note how much they vary. This will underscore the concept that there is no single frequency response for any room - it varies greatly throughout the room in all three dimensions.


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

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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 18:04:15 (permalink)

    I had avoided focusing on the phrase: "a reasonably flat uncalibrated (omni) mic" because I had trouble defining "reasonably" for myself.

    For example; I do not consider the graphed results of the 85 Behringer mics shown above to seem all that flat, but they seem to sneak in at +/-3dB 20Hz through 10kHz so I guess that's sort of flat.

    I agree that typically, room resonances and nulls, as illustrated in the 2nd illustration, are even greater considerations. The graph of the room shows a 30dB peak to dip no matter what mic used.


    best regards,
    mike


    post edited by mike_mccue - 2012/03/29 18:05:39

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    drewfx1
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 18:31:56 (permalink)
    mike_mccue


    I had avoided focusing on the phrase: "a reasonably flat uncalibrated (omni) mic" because I had trouble defining "reasonably" for myself.

    For example; I do not consider the graphed results of the 85 Behringer mics shown above to seem all that flat, but they seem to sneak in at +/-3dB 20Hz through 10kHz so I guess that's sort of flat.

    Hard to tell from that graph how many of the mics vary how much from "flat". It's a fairly large number of mics and the lines are needlessly thick and all the same color (which makes me su****ious, but you know I'm like that). So you can't really tell exactly how many of the mics fall where. Do they post the data in a different format?

      "The original X1"
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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 18:55:00 (permalink)
    I didn't look for an individual graph, and I agree with you assessment about being hard to tell, but I tried to take all that into account with my estimation of +/- 3dB from 20Hz-10kHz.

    It seems like +/-3dB describes 2 points right in the center of the range of levels depicted by the red jumble at 20Hz and at 10kHz. A statement of +/-6dB would be more descriptive of a worse case scenario.

    That's all I was thinking... it wasn't very scientific. :-)


    best,
    mike

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    mike_mccue
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 19:04:25 (permalink)
    Here's the Behringer with skinny lines from a link found at the link Corey posted to:



    http://translate.google.c...temid%3D66&prev=hp






    OK: There are individual graphs at the bottom of the link Corey posted to. These seem to be suitable as direct response to your inquiry but I can't get the images to show. The blog server seems to shut them off for remote loading.


    best regards,
    mike

    post edited by mike_mccue - 2012/03/29 19:10:35

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    drewfx1
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    Re:Supersimple superficial room check - a waste of time? 2012/03/29 19:27:44 (permalink)
    Thanks! That looks closer to the sort of bell curve distribution I would expect.

    But of course if you don't do some sort of calibration, you'd have no way of know if you happen to have one of the really inaccurate mics.

    But generally things only seem to really get inaccurate at higher frequencies, regardless.

      "The original X1"
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