• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

UMIK-1 or any USB MIC unsuitable for timing measurements?

Keith_W

Major Contributor
Joined
Jun 26, 2016
Messages
2,759
Likes
6,373
Location
Melbourne, Australia
@UliBru pointed out to me that some microphone calibration files may be supplied as inverted, and some are not inverted. The non-inverted files require inversion before they can be used to correct your microphone's calibration. The way to recognize which is which is to examine your mic calibration file and look for a peak at 10kHz. If the peak is negative, then it has already been inverted. Otherwise, check with your mic manufacturer whether the files are supplied as inverted or not.

Acourate forces you to examine the mic calibration file and decide if you wish to perform the inversion. I have never seen any other package even mention this as a problem.
 

andyc56

Active Member
Joined
May 14, 2016
Messages
122
Likes
170
I have been happily using a UMIK-1 and REW for DIY speaker tuning and room EQ and it seemed like it was working OK. I am starting on a new speaker project and decided to get a little more serious and look at CAD help. When reading through the documents for VituixCAD I came across this in the "how to measure using REW section".

VituixCAD documentation said:
Note! Single channel measurement systems such as USB microphones (with latency variations by default) are not recommended for speaker engineering due to timing and phase variations and normalizations. REW should NOT be used without electrical loopback as timing reference or cal and timing reference for acoustical measurements to avoid timing manipulation by the program.

This reminds me of a similar mistake I made years ago when MSO was very new. The MSO docs at the time said that USB mics were not usable for gathering MSO measurements. This was correct back then, as REW did not yet have the acoustic timing reference feature.

A miniDSP applications guy found out about MSO and contacted me, saying that John was going to add the acoustic timing reference feature to REW. After hearing that, I remember thinking something like, "This can't possibly work. MSO uses measurements at multiple positions. With an acoustic timing reference, a different measurement position means the timing reference changes, because the distance between the reference speaker and the mic changes with mic position."

But then I realized that assumption was wrong, for a subtle reason.

Here's a summary of what is required for two timing references to be the same.
  • With a loopback timing reference and XLR mic, the timing reference is always the same for all measurements
  • For two measurements using an acoustic timing reference to have the same reference, these two conditions must be met:
    • For both measurements, the speaker producing the acoustic reference must be the same
    • For both measurements, the mic position must be the same
For complex summations of measurements to give the correct result, all the measurement quantities to be summed must have been taken with the same timing reference. So if the measuements were taken with an acoustic timing reference, they must meet the two criteria above for the complex summation to be valid (same reference speaker, same mic position).

In MSO, all complex summations are performed with data taken at the same listening position. There are no "cross-position" complex summations in MSO. That's why the REW acoustic timing reference works with MSO. The summations consist of all the contributions of a set of subs at a given listening position. At a different position, the timing reference is different, but all those measurements have the same timing reference according to the above criteria.

Let's take an example where a USB mic with acoustic timing reference won't work.

There's an ambitious DIY project I've noticed: making a DIY version of the Klippel loudspeaker measurement system. The whole point of the Klippel system is to characterize the behavior of a single source at multiple positions. So if there is complex arithmetic involved, it's hard to see how it would not involve cross-position calculations. That won't work for a USB mic with an acoustic timing reference at all.

If one were working on such a project and the USB mic gave bad results (which it will), it would be throwing out the baby with the bathwater to say that USB mics are unsuitable for all phase-sensitive applications. They're only a problem when cross-position complex math needs to be done on the results.
 

Dave Bullet

Member
Joined
Oct 30, 2022
Messages
70
Likes
100
Just so we are clear about inversion or not on MIC calibration files. Here's my UMIK-1 supplied calibration file:
1712712430231.png

Here is the measured response of a waveguided tweeter (SB26ADC in VIsaton WG148R waveguide with felt throat adapter):

Purple is the "no calibration supplied" measurement. Green is after applying the above calibration. As such I think calibration is correct when using REW. I can't recall any requirement to invert the calibration in the REW manual.
1712712502148.png
 

Balle Clorin

Major Contributor
Joined
Dec 26, 2017
Messages
1,395
Likes
1,264
A Dayton xlr mic and a Scarlett solo or 2i2 works very well and is a cheap entry
My Scarlet Solo is crap, inconsistent and variable and wobbly frequency response.Results are misleading and incorrect.
 
Last edited:

johny_2000

Active Member
Joined
Feb 24, 2024
Messages
142
Likes
65
Location
Suburb of Seattle
Acoustic ref with a USB mic using a separate speaker to the one being measured can provide a stable reference even for off-axis measurements within the limits of the mic, but an analog mic and a loopback connection are better.
Does anyone know what calibration methods for Genelec and Neumann monitors they use?
An analog microphone connected via an ADC to the Ethernet port of the PC on which the software is installed?

I've heard that Genelec uses a modified DIRAC method for room EQ.
 

staticV3

Master Contributor
Joined
Aug 29, 2019
Messages
8,373
Likes
13,529
Does anyone know what calibration methods for Genelec and Neumann monitors they use?
An analog microphone connected via an ADC to the Ethernet port of the PC on which the software is installed?

I've heard that Genelec uses a modified DIRAC method for room EQ.
Neumann MA 1:
Blank diagram (27).png

Audio interface and Switch need to be purchased separately. Neumann only provide the software and mic.

Genelec GLM:
Blank diagram (28).png
 
Last edited:

doalt

Member
Joined
Feb 22, 2023
Messages
36
Likes
22
@UliBru pointed out to me that some microphone calibration files may be supplied as inverted, and some are not inverted. The non-inverted files require inversion before they can be used to correct your microphone's calibration. The way to recognize which is which is to examine your mic calibration file and look for a peak at 10kHz. If the peak is negative, then it has already been inverted. Otherwise, check with your mic manufacturer whether the files are supplied as inverted or not.
Does anyone know if the calibration file for Dayton Audio UMM-6 mic is inverted or not? I see it's a downward slope.

I just use it as is in REW. Is it possible that all my measurements are wrong?:facepalm:

屏幕截图 2024-05-16 235059.png
 

johny_2000

Active Member
Joined
Feb 24, 2024
Messages
142
Likes
65
Location
Suburb of Seattle
Neumann MA 1:
View attachment 369840

Audio interface and Switch need to be purchased separately. Neumann only provide the software and mic.

Genelec GLM:
View attachment 369839
Thanks for the block diagrams.

Does the Neumann MA-1 XLR microphone need to be connected to the USB audio input on a PC?
If this doesn't come with the MA-1, is it possible to use something like a Focusrite Scarlett Solo with a XLR mic preamp?

In this comparison, Genelec offers a USB GLM Controller that digitizes the input microphone signal and transmits the results to a computer program via USB.

Judging by the fact that the microphone in both cases is analog, the issue with their calibrations is interesting. Genelec may have integrated calibration data into the GLM Controller or PC software to correct the nonlinearity of analog microphone capsules. But Neumann is unclear how it solves the issues of calibrating microphone nonlinearity.
 

staticV3

Master Contributor
Joined
Aug 29, 2019
Messages
8,373
Likes
13,529
Does the Neumann MA-1 XLR microphone need to be connected to the USB audio input on a PC?
Yes.

If this doesn't come with the MA-1, is it possible to use something like a Focusrite Scarlett Solo with a XLR mic preamp?
Yes.

But Neumann is unclear how it solves the issues of calibrating microphone nonlinearity.
Each MA 1 microphone is calibrated at the factory. When you run the MA 1 software, you type in your mic's S/N and it loads the appropriate mic calibration file from Neumann's servers.
 
Top Bottom