The MiniDSP UMIK-1 USB Measurement Mic

The UMIK-1 Measurement Microphone

 I’ve been following MiniDSP for the last year or so.  They specialize in low-priced, programmable DSP modules – primarily for tuning home stereos and building custom active loudspeakers.  My introduction to them was by purchasing a MiniDSP 2x4, which is reminds me of a $100 miniature Meyer Galileo but with unbalanced I/O and DC power.  You choose routing, delay, filtering and parametric EQ on every in and out.  It’s a great little box (I’ll try and write about it later).

But what really caught my attention is a new MiniDSP product called the UMIK-1. It’s advertised as a omnidirectional measurement microphone but with a built-in preamp and D/A. It connects via USB and is recognized as a class-compliant (driverless) audio interface. Even more tantalizing is the price at $75 list.  The thought of being able to do transfer function (TF) measurements with nothing more than a laptop and a mic was also really appealing (that would require using the headphone jack on the computer – but for backpack studio junkies it’s really tempting).  When the mic arrived, let’s just say I was really excited!

The UMIK-1 comes with a substantial kit: microphone, windscreen, mic clamp, large-thread mic stand adaptor, miniature tripod, USB cable and a padded plastic box.  This is quite generous for a mic of any price. The mic itself is all metal, feels solid, and is about the same size as most P48 measurement mics (like the Earthworks M30).  You can look up your mic’s serial number on the MiniDSP website and download a custom correction file for trimming up the response in your measurement program.  I retrieved that file with no issues.

Testing time

The flattest mic in our arsenal is the DPA4007.  It’s standard for the Meyer SIM-3 system: with ruler-flat response and minimal phase shift. Measurement dorks come to fisticuffs when discussing the best mic – but the 4007 is my gold standard – and I chose it as the reference to do a standard mic comparison TF measurement against the UMIK.  SMAART v.7.5 and a Focusrite Scarlett 2i4 completed the test rig. 

Here is the mic compare setup.  Measurement police kitties hard at work in the background. 

For a source, I used a single JBL LSR4328P studio monitor. For a mic compare test, the only thing that matters is how broadband the speaker is, but it’s not a bad monitor (technically, it’s -10 down at 35 Hz and 25 KHz).  I fed it pink noise, launched SMAART and I was off to the race. The UMIK is in one USB port and the Focusrite in the other - and both are set to 48K. 

Then came a big letdown.  

The TF phase trace showed the UMIK sitting 180-degrees away from the DPA.  I know my workflow with SMAART and the Focusrite/DPA combo is absolute-polarity correct.  I then took a look at the UMIK impulse response (IR) trace and the spike went downward.  The UMIK is polarity reversed! With a regular analog XLR mic, this is only moderately egregious since one simple adaptor fixes it. But how do you un-flip the polarity on a USB plug? This is inexcusably bad engineering  – especially for a measurement mic.  Fortunately, polarity won’t affect single frequency response TF measurements – but the phase trace will always sit 180-degrees off across the whole band. So I set my OCD aside and continue.

Three bad thoughts.  

I won’t call the next anomaly another big letdown – mostly because it was pilot-error – but it stumped me for an hour.  As soon as I started the mic compare, I let SMAART add in the appropriate delay compensation on the reference source. The phase trace snapped to 180 (this would be zero if the damn polarity was right – but it was a nearly straight) and the coherence cleared up to >95%.  But then the phase trace slowly started to unwind!  And the coherence trace started dripping red blood all over the screen – starting in the HF and slowly cutting across the band.  I didn’t panic because I’ve seen this before.  When a rigged loudspeaker is slowly swinging you can see the same phenomena happen.  But how could my tiny home studio be collapsing?  The delay time was slowly slipping about 0.1ms of delay for each second of clock time. That would mean my monitor was sliding back 1.5” every second! 

Of course, the monitor stayed put. So my second bad thought was that there must be some stupid DSP problem in the mic that is adding delay. (To me that's plausible, given that someone designed it with wrong polarity).  So I engaged the delay tracking option in SMAART.  Sure enough, it was able to compensate, and I watched with fascination as the delay time started a slow countdown. 

Watch this video.  The first half is with no tracking – and you can see the phase trace slowly unwind as the bad coherence start to slide left.  The second half is with the delay tracking engaged and you will see the offset grow.  Sexy time!  You can download a high-res version here.

Then came the third bad thought – which was that I was just a presumptive idiot There is an inherent problem having two uncorrelated (no digital sync) digital input devices connected to the same program.  SMAART can handle as many simultaneous interfaces as you can plug into the computer – but (rightfully so) it has no method of sample-rate or sync correction.  So… how in the world can you sync two digital sources without word clock? But then I remember a stupid Avid product that never had any practical use to me... until now.  Every time you install ProTools, a rather obscure audio engine choice called “Pro Tools Aggregate I/O” shows up in your control panel.  This driver allows you to consolidate multiple interfaces into a single virtual device, which is required for ProTools 90’s-vintage input limitations. What I remembered about the aggregate device is that you can access a hidden layer that provides “drift” correction for exactly this problem.  It creates virtual digital sync.   I’m now beginning to have second thoughts about my years of Avid-bashing.  You can only access this functionality when you call up the Aggregate via the “Audio MIDI” utility in OSX (the preferences audio pane won’t do it).  I clocked both devices to the Mac internal D/A output by engaging “drift correction”.  Fortunately, this fixed the issue -- and kudos to SMAART for allowing the Aggregate choice as input.

Here are the settings that allowed Avid to fix the sync problems going into SMAART.

Finally I am up and running with a legitimate mic compare TF.  I can work around the polarity problem and now concentrate on discovering just how flat the UMIK is.   BTW, it’s not.  I ran all my TF measurements with 1/24 octave smoothing and it’s rough.  From 2k to 8k there are multiple resonant peaks – about 16 of them – upwards of +2.5dB.   My best guess is that this is the resonance of the housing or a problem with the grill. Whatever is the cause, it’s not good for a measurement mic – but it does have a tolerance of about +/- 3dB and that’s acceptable deviation and common in many popular recording microphones.

Here is the native frequency response on the UMIK-1 

I imported the correction curve provided by MiniDSP into SMAART and ran another measurement.  It made the response a bit better – but still not great.  MiniDSP claims corrected tolerance to be +/- 1dB and my measurements confirm this. 

I then decided to make my own correction curve. A correction curve is a comma delimited text file of frequency in one column and deviation in the other. SMAART is also able to export this data, which you can then paste into Excel and export as a file. 

Watch this video to see the export and creation process for my correction curve. You can download a high-res version of this video here.

The result of the correction curve was quite flat.

Here are the three curves together.  Pink = native, Blue = mfgr corrected, Yellow = custom correction 

With a reasonable correction curve, the UMIK-1 can be used as a reference mic in non-critical applications.  Impulse response (delay timing) and quick system conformity tests should be just fine with this mic.  Because I already had the JBL 4328 set up, I decided to run a final comparison by measuring an actual TF of the loudspeaker with each mic.  The results are shown below.

Pink = DPA4007, Blue = UMIK-1 

It’s not bad.  Some of the HF shift is likely due to the mics being about 2” apart with diffractive reflections stemming from being so close to the JBL waveguide.

 SOME OTHER THINGS TO NOTE

Calling this mic omnidirectional is a stretch. It’s really a “generously wide” cardioid.  It exhibits significant HF shading at 90 degrees – so much so that the mfgr. also provides a 90-degree correction curve.  You can also adjust the gain of this mic via the MacOS “Audio MIDI” control panel.  However, I could not get the sample rate to change even though MiniDSP claims it is both 44.1 and 48 – the dropdown doesn’t work in OS 10.11.

 CONCLUSION

What sells me on this mic is the convenience it provides at a very low price point.  It suffers from some bad engineering and a substandard correction curve, but it travels very easily and costs about 75% less than a decent entry-level (no correction needed) analog measurement mic.  If you can borrow an excellent mic from which to create your own correction curve, you have the means to correct for sample rate drift, and you don’t mind seeing your phase trace 180 degrees off, this is an acceptable device.  If you need it to work right out of the box, I would stay clear.

-Mike

http://www.miniDSP.com

UMIK-1 street price appx. $98 on Amazon with shipping

SIM Seminar with Bob McCarthy

UCI Sound recently hosted Bob McCarthy on campus for a seminar about SIM, Meyer Sound's advanced loudspeaker and sound system measurement tool. The seminar lasted four days, during which McCarthy filled out heads with information, demolished untruths, and taught us how to think more logically and clearly about sound systems.  Of the three faculty/staff in the sound program, I'm the only one who hadn't yet taken this seminar, so I was excited to finally be able to fix that. Bob's presentation was detailed and specific, and while there's no way that I could have retained everything he said (there were people in the class who had taken it three or more times already), I definitely have a stronger understanding about how large systems behave.  

Each of the MFA students at UCI wrote a bit about their own experience in the class. Thanks, Bob & Meyer!

-Vinnie Olivieri 

Matt Glenn:

Two years ago when I entered the MFA program at UCI, I was a stereo or 5.1 kid. I knew nothing of system design—I was a what-comes-before-the-speakers kind of guy. Through the Meyer seminars we've hosted, I've not only grasped the core concepts of speaker system design but system design has become a strong interest of mine. Bob's seminar was an incredibly engaging perspective for me—truly, it alters the way I think about sound.

Bob's seminar presented a large amount of information (and we only covered a small percentage of his book), but what stuck with me was his constant reference to his core concept of linearity in the physics of sound. In a teach-a-man-to-fish kind of way, Bob instilled these concepts so that we could derive the answer to any system design situation. One day, maybe I'll even be quick at it like Bob... but baby steps. On top of the lecture, Bob was also gracious enough to invite us to join him at the Orange County Performing Arts Center (at Segerstrom Hall) as he demonstrated his tuning methods on the [very strange-looking] hall's sound system (see the picture above). It was pretty awesome to watch Bob work, not only to see his quick problem-solving but also to learn from his inter-personal skills when completing a difficult task.

Thank you Bob, thank you Meyer, and thank you Mike, Vinnie and BC for this awesome seminar. I know at least 6dB-intellect more than I knew before.

Josh Fehrmann:

It seems that every year around a week or two before school starts, we have some sort of training seminar.  I have found these siminars to be a wonderful way to shake off the dust from the summer. SIM class was a wonderful experience and shook the hell out of any brain dust that had accumulated. In my two years at UCI, I have had the opportunity to learn a number of tips and tricks of system design and optimization from some of the best in the business.  I am so thankful for the wonderful opportunity and life long lessons I have learned from these Meyer seminars. With SIM class, I finally felt like the puzzle pieces fit together. I am so thankful to Meyer and for Bob for sharing so much wisdom and knowledge. My art can only be made better from these opportunities.

Our four days with Bob were absolutely amazing. I loved that Bob took the time to thoroughly explain his concepts for system design and optimization. It was a great learning environment. In particular, I loved his approach to combining systems. ALWAYS REMEMBER A+B= AB  and AB = “new” A . Our class also had the brilliant opportunity to watch Bob tune a large system at the nearby Segerstrom Hall. This tuning solidified the ideas we were exploring in class. Segerstrom is quite the unique space in that it is completely asymmetrical. The physical make up of the space created some unique “real world” challenges and Bob seized the opportunity to teach us ways to deal with them. I was also reminded of how important interpersonal skills are within our business. Bob is a master at collaboration and it was great to watch him interact with everyone involved. SIM class was a wonderful experience and thanks again to Meyer, Bob, and the people of Segerstrom Hall for allowing us to have had such an amazing opportunity.

Mark Caspary:

Four days with the incredibly knowledgeable Bob McCarthy was yet another spectacular once-in-a-lifetime opportunity made possible by the collaboration of Meyer sound and UCI sound design program. Bob has the ability to take the “vudu” out of sound. Bob explained all of the strange phenomena of sound with data, numbers, ratio and math. He gave us insight into far more then what was on the analyzer screen, by explaining what the sound itself was doing.  Bob's passion and upbeat antics made the drier parts of the seminars interesting and seeing and working with the SIM software and hardware has converted me to the power and specialization that that Meyer’s SIM brings to the “system tuning a optimization” playing field.  

Brian Svoboda:

We were so thankful to have spent this time with Bob courtesy of Meyer Sound.  It's not every day that you have an opportunity to hone your skills alongside one of the top sound system tuners in the world.  Bob effectively condensed several decades of experience into a 4-day seminar that covered everything from fundamentals of system design to system optimization in completely non-ideal environments.  The latter concept was fleshed out by working with Bob in Segerstrom Hall, an architecturally challenging venue with a previously non-optimized Meyer loudspeaker installation.  Observing Bob's professional and interpersonal process surrounding this optimization was fascinating and inspiring.

I was most impressed with his ability to maneuver a sound system "blind":  The data itself tells us so much about what is happening during a tuning.  Knowing how to interpret this data will give you an edge that even sophisticated speaker modeling software cannot provide.  I was equally impressed with his line array tuning process - specifically, the maximization of equal SPL coverage relying much more on positioning and relying less on level shading.

Matt Eckstein:

To say that Bob McCarty wrote the book on sound system design and optimization would be a vast understatement (although he quite literally did write the book).  Having the opportunity to soak in even a fraction of his almost-three-decades-worth of experience was the opportunity of a lifetime, an amazing start to the 2013-2014 academic year, and a perfect way to jump right into graduate school!  We all learned a lot about tuning a sound system from Bob in the classroom, but just as valuable was the experience at Segerstrom Hall, a puzzle of a hall with some very challenging tuning obstacles.

Watching Bob sculpt an optimized system (at times from scratch) using the ratios and concepts we learned in the classroom was thrilling.  Bob relied on the data from the SIM analyzer, and what he knew the sound system should be doing, to tune the hall.  On top of the practical lessons while we were tuning the Claire Trevor Theatre and the Segerstrom Hall systems, watching Bob work with our class at UCI and the union crew at Segerstrom was also a great reminder for me about the importance of communication, teamwork, and humility.  Thanks so much to Bob, Meyer Sound, and UCI for a really inspiring start to graduate studies here at UCI!!

Kelsi Halverson:

As my first activity at UCI, Bob McCarthy's SIM Training class might have been the most intimidating I could have been a part of. My initial reaction: “WHERE AM I? WHAT AM I DOING HERE? CAN I QUIT?”

Let’s be honest: Bob is a certifiable genius. His knowledge regarding all things audio is astounding and inspiring. He answered questions in ways that would make Alex Trebek weep with happiness. His description of proper line array arrangements was one of the most memorable discussions. 

In reality, minds like Mr. McCarthy’s are rare. Coming into graduate school, I know I have a ton to learn amongst people just as smart as Bob. This class helped affirm that I made the right decision coming to UCI. I am so incredibly excited to begin my three-year adventure with this incredible group of artists, friends and support system.  

BC Keller:

This is the 3rd time I've taken the SIM class with Bob McCarthy. Each time I take it, I learn more and more. It's decades of life lessons, condensed into 4 days. It's a lot to absorb. I've been asked, "why keep taking it?"

 Two reasons. 

1) Because I'm still learning new tricks from him. 

2) I want to hear what the students are being taught, so when we run into a situation, I can say, "remember when Bob was talking about...". Reinforcing the class with real world magnifies the learning experience for our students.

This year, we had the added bonus, of a field trip to Segerstrom Hall in Costa Mesa! It's one thing to see Bob tune a couple of UPJ's in the seminar. It's quite another to see how he puts system after system together in a large, complex venue! At first glance, it seems immense! But watching Bob follow his basic math equation of "A+B=AB, which is now the new A. New A + B = AB, which is the newer A..." Repeat as needed. A big thank you to the folks at Segerstrom Hall for letting us in to observe!

My favorite part of the seminar this year actually happened the week after. Matt G came to me with his slightly re-vamped design for BBAJ. Clearly the lessons hit home. As we learn in the seminar, first part of tuning the system, is picking the right speakers, and putting them in the right places. That way, you aren't wasting time in the space when you actually get to tuning the room. After the SIM Seminar, Matt had a much better understanding of how speakers interact with each other. And I hope, the front fill system will be the better for it!

Thanks again to everyone at Meyer Sound Labs! For the SIM Seminar, for the R&D that went into the development of SIM, for helping to make us better Sound Professionals. Special kudos to Gavin Canaan and Tom Cavnar for all their help. Obviously, to Bob McCarthy, for sharing his knowledge with us. And to John & Helen Meyer, for having an educational branch. And thanks to our UCI folks, who help make it happen as well: Keith Bangs, Ron Cargile, Toby Weiner. And of course, our fabulous Sound Professors, Mike Hooker & Vinnie Olivieri!