# Using USB mics and HDMI--several questions



## AustinJerry (Apr 2, 2010)

A small group over on the AVR Forum is collectively developing our REW skills using the new USB microphone support, and HDMI connectivity. Several questions keep popping up, and we would like to see if someone here can provide guidance.

Two of the popular microphones being used are the UMIK1 and the UMM-6. The UMM-6, when ordered from Cross-Spectrum labs, comes with custom calibration files. We use the “narrow_band_response_90_degree.cal” file, since we orient the microphone towards the ceiling during most measurements. The UMIK1, as I understand it, only has one calibration file, taken at a zero degree angle. How much difference will it make for REW measurements if the UMIK1 and its 0-degree calibration file is used? Are the measurements still reasonably valid?

When using the USB microphone and an HDMI connection, it has been said that the sound card calibration step is no longer required. Is this true? (Not sure how one would calibrate the sound card using this configuration.)

And finally, my understanding is that the microphone calibration step is still a requirement for the USB microphone, and that having a SPL to conduct this step is a requirement. Please confirm.

Thanks in advance for the feedback!

Edit: I am getting some pushback from thread participants. They see no reason for calibrating the mic at all. Why is mic calibration an important step?


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## stevekale (Jan 19, 2013)

JerryMeeker said:


> Why is mic calibration an important step?


Because variances from mic to mic are such that you don't have a reference point without a calibration. 










You are sending stimuli (sweep) and measuring responses. How do you know if your results aren't simply due to the response profile of your mic? Without a calibrated mic, you simply don't.


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## AustinJerry (Apr 2, 2010)

I am not sure we are talking about the same thing. It sounds like you are talking about calibrating the microphone against a known standard, generating a calibration file to correct the microphone's response characteristics, and then loading that calibration file into REW. I agree completely that this is very important, but this was to my question.

I am talking about the "SPL Meter" tool, where a signal is generated, the level of the signal is read using an SPL, and the value is entered into the mic calibration screen to set the absolute sound level for subsequent measurements. This is an entirely different question, and I am getting pushback from some who think this step is unnecessary.

Just to be clear, here is waht I am talking about:


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## stevekale (Jan 19, 2013)

My bad. The SPL meter in REW has no idea what mic and sound card you are using and is designed to work with a wide range of devices. In order to be useful it needs a reference point for your particular setup. Of course, if you have a calibrated mic and have entered that calibration file then you've given REW a reference point (at all frequencies in the calibration file) and hence you do not need to provide another.


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## JohnM (Apr 11, 2006)

The UMIK-1 cal file includes a sensitivity figure which REW can use, along with the Windows mic volume setting, to know what the actual SPL in the room is. For other mics the SPL Level Calibration is needed to tell REW how the signal level it sees relates to actual SPL, and that calibration remains valid only if the input path gain remains the same (i.e. input volume setting is not altered, preamp gain not altered if using a preamp).


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## AustinJerry (Apr 2, 2010)

John, thank you for confirming. I know that support for the UMIK-1 has been added to REW. Are there plans for adding support for the UMM-6, which is an equally popular USB mic?


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## JohnM (Apr 11, 2006)

To get REW to recognise the UMM-6 as a USB mic I would need to know how the mic identifies itself to the OS, i.e. exactly what appears in the REW input device and input selectors when a UMM-6 is connected (ideally a copy of REW's soundcard debug file generated after connecting a UMM-6). 

The UMIK cal data includes a sensitivity calibration figure in a format REW can understand, so with UMIK REW also can skip SPL calibration - I don't know whether there is any corresponding information in UMM-6 cal data. 

I would also need to know how the Windows input volume setting affects the levels coming from the mic, which may be different for Windows XP, Windows 7 and Windows 8. That involves:

- Setting up the mic pointing at and very close to (within a few inches) the midrange unit on a speaker, needs to be on a stand or supported so that it doesn't move during the test
- Opening the Windows Levels control for the mic (e.g. on Win 7/8 Control Panel -> Manage Audio Devices -> Recording Tab -> select Omnimic -> properties -> Levels tab)
- Opening the REW signal generator and start it generating a 1kHz sine wave
- Adjusting the AVR and/or REW's signal generator level so that the tone is at a decent level, shouldn't be loud in the room (since the mic is very close to the speaker) but a good level will give a more accurate result for the next part
- Opening the REW SPL meter
- Recording the REW SPL meter dB FS readings from the small figure above the horizontal bar, just below the A/C/Z weighting selector buttons, for as many Windows Level settings as one has the patience to collect, but as a minimum the levels at 100, 90, 80, 70, 60, 50, 40, 30, 20, 10 and 0.
- The final step is to place an SPL meter exactly where the mic was and record what SPL reading it shows with the sine wave playing from REW at the level used when noting the figures


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## AustinJerry (Apr 2, 2010)

John, thank you for the detailed response. Unfortunately, if you were soliciting my assistance, the procedure you have outlined is too complex for me. I believe AVS user Jevansoh has already approached you with an offer to assist in qualifying the UMM-6, so I will defer to him and wish him luck. In the meantime, I have no issue with manually calibrating the UMM-6, and am already using it successfully in REW.


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## amirm (Apr 13, 2012)

Hi John. I am due to receive my UMM-6 this week and would be happy to run the tests this weekend and report back.

Amir


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## Wayne A. Pflughaupt (Apr 13, 2006)

JerryMeeker said:


> When using the USB microphone and an HDMI connection, it has been said that the sound card calibration step is no longer required. Is this true?


John as indicated as much is previous posts.




> Two of the popular microphones being used are the UMIK1 and the UMM-6. The UMM-6, when ordered from Cross-Spectrum labs, comes with custom calibration files. We use the “narrow_band_response_90_degree.cal” file, since we orient the microphone towards the ceiling during most measurements. The UMIK1, as I understand it, only has one calibration file, taken at a zero degree angle. How much difference will it make for REW measurements if the UMIK1 and its 0-degree calibration file is used? Are the measurements still reasonably valid?


 Measurements taken with a 0-degree file with the mic upright will show a sag in response above ~1-2 kHz, or possibly other abnormalities depending things like the room’s ceiling.

Honestly, I never “got” the 90-degree orientation thing, at least for full-range measurement of the main-channel speakers. Everything I’ve ever seen in the manuals of hardware RTAs from various pro audio manufacturers (back before the days of software-based measurement) indicates that upright orientation was traditionally only used in highly-reverberant, diffuse-field environments. That certainly is not the typical home theater, even with nothing but a sofa for acoustical treatment. Basically, if you are able to localize your speakers you don't have a diffuse-field room.

Here is some more reading on the subject.

Regards, 
Wayne


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## Mike2001 (May 10, 2011)

My UMM-6 is awaiting Customs Clearance (in UK), so I hope to receive it within about a week.
I will be happy to attempt to gather the information requested by JohnM.
If all goes well I should be able to use two laptops, one running Windows XP SP3, the other running Windows 7 - both have been used in the past to run REW.
Hope this helps in getting the UMM-6 fully supported.
Regards, Mike.

Edit:-
With regards to the mic orientation debate - isn't the 90 Deg (upright) better for capturing 'room' responses, as it treats sound from speakers and reflections from room boundaries more equally. Obviously the floor & ceiling reflections will some what affected, but fully omni-directional is beyond us mere mortals.


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## WestSideVB (May 14, 2012)

Mike2001 said:


> Edit:-
> With regards to the mic orientation debate - isn't the 90 Deg (upright) better for capturing 'room' responses, as it treats sound from speakers and reflections from room boundaries more equally. Obviously the floor & ceiling reflections will some what affected, but fully omni-directional is beyond us mere mortals.


Another point on the 90vs0 degree orientation is that when we are measuring multiple speakers with a 0 degree orientation file, where do you point the mic? 90degrees always made more sense to me but that's likely because that's how I learned it for my first measurements. I agree with the room interaction point above.

Interested to hear what Wayne (and others) have to say on the topic and appreciate the information concerning the impact of using a 0 degree cal file with a 90 degree orientation.

This point is why I lean toward the Dayton over the minidsp USB mic.


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## WestSideVB (May 14, 2012)

JohnM said:


> To get REW to recognise the UMM-6 as a USB mic I would need to know how the mic identifies itself to the OS, i.e. exactly what appears in the REW input device and input selectors when a UMM-6 is connected (ideally a copy of REW's soundcard debug file generated after connecting a UMM-6).
> 
> The UMIK cal data includes a sensitivity calibration figure in a format REW can understand, so with UMIK REW also can skip SPL calibration - I don't know whether there is any corresponding information in UMM-6 cal data.


Has anyone verified if the Dayton cal files contain a sensitivity figure?


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## Wayne A. Pflughaupt (Apr 13, 2006)

Mike2001 said:


> Edit:-
> With regards to the mic orientation debate - isn't the 90 Deg (upright) better for capturing 'room' responses, as it treats sound from speakers and reflections from room boundaries more equally.


Why would you want to equalize your speakers based on reflections from boundaries? If you close your eyes and play a single speaker, can you point to where it is? If so, then that’s primarily what you’re hearing, not what’s coming from all the reflections. 




WestSideVB said:


> Another point on the 90vs0 degree orientation is that when we are measuring multiple speakers with a 0 degree orientation file, where do you point the mic? 90degrees always made more sense to me...


How much faith do you want to put in a measurement like that? Running all the speakers at the same time, you’re quadrupling the amount of reflections in the room that are being generated by four additional discrete sound sources (assuming a five-channel system). That’s a pretty messy proposition, sonically speaking, especially in an asymmetrical room like most people have.

I guess it’s an okay technique if you merely want an “FYI” reading on what all the speakers playing at once are doing, but you surely would not want to do any per-channel equalizing based on such a measurement. If you notice an abnormality in combined response, you need to figure out if it’s coming from a particular speaker(s) and deal with it (them) specifically, especially if you have non-matching speakers around the room and/or asymmetrical placement.

As we all know, most of the auto-EQ systems out there these days work from a vertical mic orientation. If you look at the links in my previous post you’ll find this one that talks about how a measurement with 90-degree orientation could easily be skewed by reflections, even with the correct calibration file. If we added a second identical speaker at the back of the “room” in the picture, it’s much closer to the mic than the front one, so its first reflections from the ceiling would not even “hit” the mic element. So an auto EQ system would equalize the two speakers differently.

We also know that there are people who claim they haven’t been happy with the results of their receivers’ auto-EQ systems. Sure, at least some of that can be because some of those systems are more effective than others. But putting that aside for a moment and assuming equal capability - I can’t prove this (one would have to actually be there to study each situation specifically), but I’m fairly certainly the problem much of time is something with their particular room that is enhanced (made worse) by the vertical mic orientation. This is what can happen when the measurement technique “accumulates” too much information from reflected signals, to the detriment of the primary signal (that being the speaker itself).

Regards, 
Wayne


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## WestSideVB (May 14, 2012)

I listen to my speakers, usually more than one at a time, inside a room which is not anechoic. Also my ears are on the side of my head.

Wayne, I understand what your saying and yes I do individual speaker measurements but when I'm optimizing the transition range between mains and subs or trying to figure out if my mains positioning are good and audyssey behaved as intended I am wanting to be able to compare individual speaker measurements to multiple speaker measurements to see the speaker-speaker interaction. And I want all these measurements to take into account the room as closely as possible to the impact the room has on what I perceive I hear. Also If I were pointing at particular speakers I would have to move that mic around all the time during an REW session and we know how much minor mic positional differences impact the results. What about when working on my multiple subs, where do I point it then?

To each his own but I'm not reading anything to sway my thought process thus far. I appreciate your thoughts on the subject though.


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## mogorf (May 27, 2009)

Hi,

Of course, I do agree that the best is to have a set of calibration files with different orientations prepared by specialists, but I’d like to talk a bit about the UMIK-1 (or any other mic with only 1 cal file) as an example with an idea to discuss how a self-generated cal file can be produced for 90 degrees when only the 0 degree file is provided by the maker and how the UMIK-1 owners or wannabee owners can regain their self-esteem and feel like half a man no more before cancelling their orders or shipping back/selling out their stock. 

Before going into details, let’s review again some aspects of measuring mics:

1. I think we can easily agree that the directionality of the mic is only relevant at the high frequency end of the audio spectrum, while the lower we go down the importance becomes less important in view of sensitivity. Finally, down at the Bass Department the orientation makes no difference, for such large wavelenghts the mic can be in any position, up or down or on-axis or even showing it’s back side to the sub.

2. Most of the commercially available test mics use a Panasonic capsule, therefore the basic characteristics will be more or less similar, while some deviation may be attributed to the housing. Namely they will have a pretty flat response up to about 3-4 kHz and the curve will have a peak around 13 kHz, from thereon it will start to rolloff. This 13 kHz peak will be somewhat higher for on-axis and somewhat lower for grazing incidence.

3. The range above 10 kHz will be of less importance when it comes to measurements of seating positions because that range is less sensitive to in-room speaker placement. Although a non-calibrated mic position may show HF roll-off, it won’t (shouldn’t) inlfuence waterfalls and spectrograms, it will just not look right on the SLP charts.

4. Nonetheless, in order not to worry about the HF rolloff (seen on the charts but not present in reality) caused by non-calibration it’s advisable to load the relevant mic file into REW.

OK, not let’s take the UMM-6 mic with two response curves ( 0 and 90 dgerees) as an example and let’s have a closer look at this graph:










We can see that the lower end below 3-4 kHz is pretty much the same regardless of mic orientation, while the 0 degree curve (red) will need more compensation than the 90 degree curve (blue). (For the time being we may omit the 45 degree curve from our discussion.)

Here’s the table from CLS site for 0 degrees of the above chart with numbers:










Since the UMIK-1 usb mic is shipped with only 1 cal file for 0 degrees (on-axis) and more or less will show the same or similar characteristics on the occasion of being another Panasonic capsule type mic, my idea would be to modify the supplied table starting from 2.5 kHz and up by simply reducing the dB values by approx. 50%.

When done, the new figures can be copied/pasted into a notepad file which will be saved with a .txt extention. This .txt file will be the new cal file for the UMIK-1 for grazing incidence and can simply be loaded into REW. Job done.

Let me know what you think, please. Good or bad, all.

Thank you for your attention.

Cheers, Feri


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## Wayne A. Pflughaupt (Apr 13, 2006)

Hey WestSide,

I understand what you’re doing, and it really has nothing to do with what I was writing about, which was per-channel equalization of the main speakers (just in case that wasn’t obvious in the first and third paragraphs of my post  ). The issue there is that the mic is increasingly directional at the upper frequencies, so for accurate upper-frequency readings mic orientation is critical. 

Again, this is for the purposes of equalizing. With what you’re doing - optimizing the transition between subs and mains and a general comparison between the speakers or combinations of speakers - mic orientation doesn’t matter at all: Any measureable (or audible) speaker-speaker or sub-speaker interactions will be happening well below the frequency point where the mic becomes omnidirectional. In that range there is no escaping “the impact the room has on what you perceive and hear” even if you wanted to. 

My problem, it seems, is too often jumping to the conclusion that people are taking frequency response measurements because they want to equalize, since that’s about the only thing I personally use REW for. My apologies! :hide:

Regards, 
Wayne


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## WestSideVB (May 14, 2012)

Wayne A. Pflughaupt said:


> Hey WestSide,
> 
> I understand what you’re doing, and it really has nothing to do with what I was writing about, which was per-channel equalization of the main speakers (just in case that wasn’t obvious in the first and third paragraphs of my post  ). The issue there is that the mic is increasingly directional at the upper frequencies, so for accurate upper-frequency readings mic orientation is critical.
> 
> ...


Roger that, I'm learning and appreciate your thoughts. I don't even have EQ for my mains (other than Audyssey XT32). I have nothing manual up there. I do look at the FR of the mains and tweak what I can. So as I am now figuring out this positioning thought process I think so much about and am so tedious about has absolutely no impact on what I am using REW+the mics for.

Seriously if my wife watched me do an REW and Audyssey re-run session she'd definitely think I was so crazy she'd move back to Germany. LOL

Thanks for your time


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## amirm (Apr 13, 2012)

WestSideVB said:


> Has anyone verified if the Dayton cal files contain a sensitivity figure?


I just got mine and yes it does have that.


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## WestSideVB (May 14, 2012)

amirm said:


> I just got mine and yes it does have that.


schweeet, thanks


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## baniels (Nov 9, 2006)

That's good to hear. I wonder if that means it is just a matter of time before the UMM-6 can have the same SPL-meter-free support as the UMIK-1. 



amirm said:


> I just got mine and yes it does have that.


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## WestSideVB (May 14, 2012)

baniels said:


> That's good to hear. I wonder if that means it is just a matter of time before the UMM-6 can have the same SPL-meter-free support as the UMIK-1.


It means it is possible for the UMM6 to have the same support built into REW as the UMIK1 with respect to the SPL meter not needing the calibration step. We are asking and hoping JohnM will build that. He asked for the input so it looks promising, but I don't want to put words in the man's mouth.


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## JohnM (Apr 11, 2006)

amirm said:


> I just got mine and yes it does have that.


Could you post the cal file here for me to take a look at?


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## sonic_blue (Jan 24, 2013)

JohnM said:


> The UMIK-1 cal file includes a sensitivity figure which REW can use, along with the Windows mic volume setting, to know what the actual SPL in the room is.


Does this mean SPL calibration in REW is not required for the UMIK-1 even when using analogue output from my laptop's soundcard? Or is this for HDMI only? 

Thanks


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## AustinJerry (Apr 2, 2010)

JohnM said:


> Could you post the cal file here for me to take a look at?


I have attached the files I received with the UMM-6.
View attachment UMM-6 Calibration Files.zip


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## baniels (Nov 9, 2006)

Attached is the txt file from Dayton for your mic. It lists the sensitivity as -23.555dB. I downloaded it from here after seeing the serial number in your CSL zip. I've been waiting for someone to post one of these, so thanks. :T

Here is how the Dayton supplied cal compares to the CSL 0 and 90 degree narrow band cal files. I assume the Dayton file is for 0 degrees, but I'm not sure. 

Note the scaling. I wasn't sure the appropriate way to show these. I attached the mdat file.


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## WestSideVB (May 14, 2012)

Progress is happening ITT, I like the way you fellas roll.




sonic_blue said:


> Does this mean SPL calibration in REW is not required for the UMIK-1 even when using analogue output from my laptop's soundcard? Or is this for HDMI only?
> 
> Thanks


The latest versions of REW utilizes a sensitivity value from the UMIK-1 cal file so the SPL meter calibration step is not required. The way you output to your AVR is irrelevant. 

I don't think the minidsp mics are individually calibrated though so you could be like .5db off. If you get that close you are far past good enough.


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## sonic_blue (Jan 24, 2013)

WestSideVB said:


> The latest versions of REW utilizes a sensitivity value from the UMIK-1 cal file so the SPL meter calibration step is not required. The way you output to your AVR is irrelevant.
> 
> I don't think the minidsp mics are individually calibrated though so you could be like .5db off. If you get that close you are far past good enough.



Thanks. I guess I'm still a bit concerned that my laptop's analogue audio out is not actually producing the level that REW has told it to throughout the whole frequency range, whereas with a HDMI or digital audio out you can be pretty much guaranteed that it is outputting a discrete and accurate signal level (or maybe not?). I notice they sell USB -> HDMI adaptor (with audio) for around $50 which could be useful.


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## AudiocRaver (Jun 6, 2012)

> I don't think the minidsp mics are individually calibrated though so you could be like .5db off. If you get that close you are far past good enough.


Every UMIK-1 is individually calibrated, with a unique calibration file for each microphone by serial number.



> Thanks. I guess I'm still a bit concerned that my laptop's analogue audio out is not actually producing the level that REW has told it to throughout the whole frequency range


There are going to be HF and LF rolloffs, and unfortunately with a USB mic there is no way to calibrate the PC output alone to know how much they are or compensate for them.



> whereas with a HDMI or digital audio out you can be pretty much guaranteed that it is outputting a discrete and accurate signal level (or maybe not?). I notice they sell USB -> HDMI adaptor (with audio) for around $50 which could be useful.


With a USB mic, HDMI out is the most accurate way to go, the measurement PC is not introducing any analog inaccuracies.


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## Chad B (Oct 7, 2011)

baniels said:


> Attached is the txt file from Dayton for your mic. It lists the sensitivity as -23.555dB. I downloaded it from here after seeing the serial number in your CSL zip. I've been waiting for someone to post one of these, so thanks. :T
> 
> Here is how the Dayton supplied cal compares to the CSL 0 and 90 degree narrow band cal files. I assume the Dayton file is for 0 degrees, but I'm not sure.
> 
> Note the scaling. I wasn't sure the appropriate way to show these. I attached the mdat file.


Are these cal files for the same mic? If so, does it mean Dayton's cal file is much less accurate and precise than the cal file from CSL? I was thinking about getting one of these mics from Parts Express, but unless I'm misunderstanding your post I may reconsider.


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## baniels (Nov 9, 2006)

Yes, they are for the same mic. I guess that is the conclusion to draw. The cost is the same or very close to buy it from CSL. No reason not to have the security of knowing it was calibrated by a trusted person with good equipment. 

Here is mine. All the comparisons I've seen have been similar to this.





Chad B said:


> Are these cal files for the same mic? If so, does it mean Dayton's cal file is much less accurate and precise than the cal file from CSL? I was thinking about getting one of these mics from Parts Express, but unless I'm misunderstanding your post I may reconsider.


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## Chad B (Oct 7, 2011)

baniels said:


> Yes, they are for the same mic. I guess that is the conclusion to draw. The cost is the same or very close to buy it from CSL. No reason not to have the security of knowing it was calibrated by a trusted person with good equipment.
> 
> Here is mine. All the comparisons I've seen have been similar to this.


Thanks for the explanation and for posting yours. 

I agree, no reason not to buy it from CSL except that Parts Express is local to me and they are my favorite store. I get more excited about their annual tent sale than my own birthday.:hissyfit:


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