# UCA202 Confusion!!



## Big Red Machine (Jan 29, 2010)

Trying to calibrate a Vista Dell Laptop. Cannot find any audio mixer controls. I get this graph and lots of errors. The RS meter is not connected at all. Is that correct?

Frustrated I cannot figure this out after reading the UCA thread.


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## Big Red Machine (Jan 29, 2010)

I am assuming this is the same thing but this instruction means nothing to me. I assumed somebody would have given me some advice by now?

"If the measurement looks like this:
Bad soundcard calibration result

it is probably due to a feedback loop from the Line In to the output. This can happen if the soundcard has some feature for record monitoring - for example, on the Soundblaster Live 24-bit External there is a "Monitor" feature for the Line In that must be turned off to get correct results, on some other Creative soundcards (e.g. Audigy 2 ZS) there is a Record Advanced Controls setting for "Record without monitoring" that must be selected. It can also happen if "Line In" is not muted in the Playback mixer for the soundcard."


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## Big Red Machine (Jan 29, 2010)

This instruction seems contradictory. Do I loop the right to right when checking the Loopback button or left to left?

"Input Channel
REW only uses one soundcard channel to capture the output of your SPL meter or mic preamp, the Input Channel control tells REW which channel you have connected to. The default is the Right channel. *If Use Loopback as Timing Reference has been selected in the Analysis Preferences the other channel will be used a reference to eliminate time delays within the computer and soundcard, this requires a loopback connection on the reference channel.* If the soundcard (or something else in the input chain) inverts its input select the Invert checkbox to restore correct polarity. If the input has a DC offset check the High Pass box to have REW automatically apply a 2Hz high pass filter. "


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## Big Red Machine (Jan 29, 2010)

Do I click this box for my old RS meter when doing the calibration? Or after the calibration is finished?

"Mic/Meter Preferences

The Mic/Meter Preferences allow selection of the Mic/Meter type, loading/clearing of a mic/meter calibration file to use for new measurements and calibrating the REW SPL meter's SPL reading.

Mic/Meter Preferences

Type

Select the C Weighted SPL Meter check box if you are using a C weighted SPL meter as the input to REW, subsequent measurements will then be corrected to remove the low and high frequency roll-offs of the C weighting characteristic. If a cal file is loaded the correction will only be applied outside the frequency range covered by the cal file. "


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## JohnM (Apr 11, 2006)

The graph you posted is the Scope plot, it shows the time signal that was captured so it is correct for it to have roughly that appearance. To examine the response use the SPL & Phase plot.


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## JohnM (Apr 11, 2006)

Big Red Machine said:


> This instruction seems contradictory. Do I loop the right to right when checking the Loopback button or left to left?


You are calibrating the channel you will be measuring with, normally that is the Right channel.


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## JohnM (Apr 11, 2006)

Big Red Machine said:


> Do I click this box for my old RS meter when doing the calibration? Or after the calibration is finished?


After the soundcard calibration is finished, it is not needed until you connect the RS meter.


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## Big Red Machine (Jan 29, 2010)

I have the right input and right output connected and no other connections except the USB to the laptop. The Monitor switch is off and the green light is on.

I get this when calibrating:


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## Big Red Machine (Jan 29, 2010)

See anything wacky here?


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## Big Red Machine (Jan 29, 2010)

I changed the buffer to 64k and looky-here. Now what the do I do?


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## EarlK (Jan 1, 2010)

> See anything wacky here?


> Yes ! ( You have the wrong input channel selected >> Right input , instead of Left, which would match to where you have signal showing ) .

> Now that you have just completed a good soundcard calibration ( obviously ), how about showing a screen shot of the preferences page as it now exists ( you must have changed more than just the buffer size ) .

<> :sn:


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## Big Red Machine (Jan 29, 2010)

It is exactly the same. The instructions said to connect right to right and select right. Why would I select left when no cables were ever mentioned to be connected at left to left?


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## EarlK (Jan 1, 2010)

Ahhh , Okay !

My mistake, since I see input showing on the left meter, I assumed that was the channel you'd decided to create your loop-back/calibration from . 

<> :sn:


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## Big Red Machine (Jan 29, 2010)

I am not sure what, if any smoothing to apply. What is reasonable to not make it look too sexy?


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## Big Red Machine (Jan 29, 2010)

BTW, that is both stereo channels running at one time. I have dual volume controls and I should run each independently to see how each channel looks. I was in a hurry to see if I could get "something"!!!


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## Big Red Machine (Jan 29, 2010)

Waterfall of left and right overlayed:


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## aackthpt (Jan 24, 2011)

Big Red Machine said:


> I am not sure what, if any smoothing to apply. What is reasonable to not make it look too appealing?


Standards for sound rooms generally suggest 1/3-octave smoothing for full range sweeps as acceptance criteria. I generally use that level when I am looking a roughly 500 Hz and above.

For a range of 200-500 Hz, I will look at a range of values. 1/48 and 1/24 are about right to look at comb filtering effects that might be mitigated by speaker placement changes.

For below 200 Hz you would want to use unsmoothed, 1/48 or 1/24 to look at features you might be able to change with EQ and see the effects of room modes.


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## Big Red Machine (Jan 29, 2010)

Is there a way to smooth separate frequency ranges with the tool? Not sure how to grab certain ranges and apply smoothing levels you suggest.

This is a 2 channel set-up so no subwoofers and no EQ'ing. This is a mature room that sounds great but I want to tweak a little.

I made my own Prime 53 diffusors for the walls last year.


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## aackthpt (Jan 24, 2011)

Big Red Machine said:


> Is there a way to smooth separate frequency ranges with the tool? Not sure how to grab certain ranges and apply smoothing levels you suggest.
> 
> This is a 2 channel set-up so no subwoofers and no EQ'ing. This is a mature room that sounds great but I want to tweak a little.


Yeah, I think I saw that room a couple weeks ago. :heehee: Good to see you here.  That room sounded pretty fantastic, BTW, I wish I'd spent more time in there, maybe brought my own CDs, spent some time fiddling with the equipment. I'd also love to test your diffusers vs. the same design finned - unfinned is so much easier to build but theoretically not performing as well - though unfinned may have a few advantages too. But I digress!

I do a few different things. One is that I just smooth the curve different ways serially and sort out the effects and frequency ranges I'm looking for in my brain. Since the smoothing changes the curves so much and I don't really "apply X smoothing for X frequency range" by recipe, and I like to see it at different smoothing at most of the ranges, it's just faster to do it that way. But one thing I occasionally do is run a sweep 0-200 Hz and a sweep from 0-20 kHz. Note that in the "All SPL" tab, when you apply the smoothing it only gets applied to the currently selected curve. So I just turn on only the full range sweep, apply 1/3 smoothing, switch to only the LF curve and apply 1/48 smoothing, then turn them both on together. This gives you a very smoothed full range curve with a relatively unsmoothed LF curve overlayed on it. I rather like the effect, and it's convenient for posting in forums.

So, you could do that but in three ranges (like 0-200, 0-500, 0-20k) which would give you three curves in the LF region. You could also do sweeps 0-200, 200-500, and a 500-20k and smooth each of them separately as desired, but I have heard it is better to start and stop test sweeps with some margin beyond the range. With that in mind you might want to provide 1/3 octave overlap at the ends of your test ranges... or at least try it both ways and see if it's any different. If the SPL and phase graphs come out the same, then good enough, no overlaps are required.

I should add that the frequency ranges I look at for different effects are not necessarily fixed. The ranges you need to consider for each type of effect are a combination of Schroeder frequency (for modal range) and room size/treatment (SBIR/comb filtering effects are dominated by reflection strength and timing). For the Schroeder frequency/acoustical ranges I like to use Bob Golds Room Mode Calculator. For example, for my room the relevant section says:

```
Frequency Regions:
 - No modal boost: 1hz to 29hz
 - Room Modes dominate: 29hz to 125hz
 - Diffraction and Diffusion dominate: 125hz to 500hz
 - Specular reflections and ray accoustics prevail: 500hz to 20000hz
```
The SBIR is not quite so simple, but you are mostly concerned with the first notch frequency which can be easily found with this calculator. Note that the calculator works the same way for floor/ceiling/sidewalls. You could do front/rear walls with it and some geometric thought, but with REW you mostly just skip this all anyway - once you learn to recognize the distinctive deep/narrow null you can just read them from your sweep results to figure out the frequency range in which you are most concerned about the effect.

The more sophisticated way to analyze all of this is using time response data; for above LF the ETC (a type of impulse response graph) thread started by mtbdudex on AVS is a pretty good start for that (and make sure you know the usable upper limit of the RS meter since I think you are using that for a mic). For LF room mode analysis the better tools are decay/waterfall/spectrogram. It's unfortunate that most never go beyond frequency response. The time response data generally shows data that guides you much more directly to solutions.


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## Big Red Machine (Jan 29, 2010)

I received a Dayton mic and 802 preamp Saturday. As requested (but I measured on stereo mode vs. individual channels):


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## aackthpt (Jan 24, 2011)

Congrats on going to better equipment! Looks like a good sweep, and actually a pretty good overall response. No way to know if the comb filtering evident between 70 and 300 is between the speakers or due to in-room reflections, though I also wonder if your dip at 70 is due to being in the null of the first vertical axial mode.


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## Big Red Machine (Jan 29, 2010)

Bob Gold output: room is 8 foot high, 13' 8" wide, and both 16' 4" deep with another alcove adding another 40". I am sitting 6 inches off-center to the right. I am wondering if since the 70hz is due to the height I may not be able to squelch this.

Freq % Wavelength, 1/2, 1/4 p,q,r Mode Group Weighting 
28.7 hz 39'4", 19'8", 9'10" (1,0,0 Axial) Start iso, End iso 
41.3 hz 30.5% 27'4", 13'8", 6'10" (0,1,0 Axial) Start iso, End iso 
50.3 hz 17.8% 22'6", 11'3", 5'7" (1,1,0 Tangential) Start iso, End iso 
57.4 hz 12.3% 19'8", 9'10", 4'11" (2,0,0 Axial) Start iso, End iso 
70.6 hz 18.6% 16'0", 8'0", 4'0" (0,0,1 Axial) 
70.8 hz 0.2% 15'12", 7'12", 3'12" (2,1,0 Tangential) Start iso, Near 
76.2 hz 7% 14'10", 7'5", 3'8" (1,0,1 Tangential) 
81.8 hz 6.8% 13'10", 6'11", 3'5" (0,1,1 Tangential)


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## aackthpt (Jan 24, 2011)

I would run your room with both depth dimensions in Bob Golds calculator, as the modal behavior would be somewhere between the two. I was thinking about that in context of your L-shaped room before, but I forgot to mention it. My room, actually, acts like a combination of the the room at its natural length, and that plus the depth of the closet in the rear so while it's not as obvious I have a somewhat similar situation, though with a lot less of a dimension difference. Anyway, I knew the first mode of 8 feet is always 70 Hz; it's a very common issue. :bigsmile: I've seen some companies specifically selling corner panel absorbers specifically tuned to that frequency even.

What you need to do is figure out if it is a mode or a reflection issue. One way I'd do this is to use the signal generator in REW to play sine waves at 69/70/71/72 Hz, and while it is dwelling on an individual frequency to move the SPL meter (or the REW mic using the REW SPL meter) around the room - into the corners, up/down/left/right from the listening position, etc. If you see and hear large variations in SPL characteristic of room modes, you have a modal issue at that frequency on your hands.

The way to find out all the frequencies at which you are likely to have modal problems I got from some guys on gearslutz: drive a small sealed subwoofer into a corner, and into another corner put the microphone. Or do the best you can anyway... at least just put the mic in a corner. Since pressure maxima of all modes appear in corners (at least in rectangular spaces, I'm not 100% sure this rule applies for irregular spaces), the waterfall/decay/spectrogram of a sweep done with this measurement position will show you all frequencies at which the room has modal energy storage, independent of listening position. Then you can correlate that information to listening position results.

Given the acoustical lengths you've gone to so far, I don't think controlling a 70 Hz mode is likely impossible. There are a number of acoustical devices you can use for damping at that frequency.


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