The moving microphone method (MMM) for Dummies using REW

[Sokel]

I don't think I understand your question now.
I entered this value, then pressed the “Play” button and then adjusted the volume on the audio interface until I reached 80 dB(Z) S in the SPL meter.
I then started the measurement.

How did you calibrated the SPL meter prior to measurements?

 

[Waldemar-Johann]

How did you calibrated the SPL meter prior to measurements?

Good evening Sokel,
thank you for your interest and help.

Now I am totally confused or have I completely misunderstood or misinterpreted something?
I used the instructions (MMM) as described in this thread to make these measurements.
I also used the "SPL Meter" app on my iPhone to check the volume for the measurement.

 

[Soniclife]

I don't think I understand your question now.
I entered this value, then pressed the “Play” button and then adjusted the volume on the audio interface until I reached 80 dB(Z) S in the SPL meter.
I then started the measurement.

That sounds right.

 

[Sokel]

Good evening Sokel,
thank you for your interest and help.

Now I am totally confused or have I completely misunderstood or misinterpreted something?
I used the instructions (MMM) as described in this thread to make these measurements.
I also used the "SPL Meter" app on my iPhone to check the volume for the measurement.

Good evening Waldemar

If I got the instructions right, they assume that SPL level on REW's side is already calibrated or they take the UMIK for granted (as it has its own cal file)
To calibrate the level shown on REW, you have to do it against a know measurement, like the iPhone you mention.

It's not difficult, just hit the SPL meter tab > press calibrate > use speakers cal signal and enter the value you see on your phone.
You can do it at a comfortable level and make sure phone and REW use the same weighing (A, C, Z, whatever) and they are both located at roughly the same spot.

 

[Waldemar-Johann]

Good evening Waldemar

If I got the instructions right, they assume that SPL level on REW's side is already calibrated or they take the UMIK for granted (as it has its own cal file)
To calibrate the level shown on REW, you have to do it against a know measurement, like the iPhone you mention.

It's not difficult, just hit the SPL meter tab > press calibrate > use speakers cal signal and enter the value you see on your phone.
You can do it at a comfortable level and make sure phone and REW use the same weighing (A, C, Z, whatever) and they are both located at roughly the same spot.

Hello Sokel,
thanks for your help!

I assumed that if I don't have a measurement microphone that is also calibrated in terms of volume, such as UMIK, I would now have to do this procedure to get more values for the next upcoming measurements.
If this is not the case, I have apparently not understood everything correctly or am not in a position to carry it out correctly.
At this point I would be prepared to order a UMIK so that I don't have to do this step now.
I will do what you have written tomorrow at my leisure.

Thanks to everyone who is helping me now, but I am very unsure from all the information where I stand now in my process?

 

[Salt]

Good evening Salt,
thank you for your interest and help.

I am willing to move the speakers for testing, but where?

Good evening Salt,
thank you for your interest and help.

I am willing to move the speakers for testing, but where?

Wherever there is a place for it to see if room modes define the dip around 80 Hz.

 

[Waldemar-Johann]

Good evening Waldemar

If I got the instructions right, they assume that SPL level on REW's side is already calibrated or they take the UMIK for granted (as it has its own cal file)
To calibrate the level shown on REW, you have to do it against a know measurement, like the iPhone you mention.

It's not difficult, just hit the SPL meter tab > press calibrate > use speakers cal signal and enter the value you see on your phone.
You can do it at a comfortable level and make sure phone and REW use the same weighing (A, C, Z, whatever) and they are both located at roughly the same spot.

Hello Sokel,
I have now done it as you said, see attachment.
The difference between the iPhone and the Mess Microphone was 1.5 dB.

All the best and a good start in the week
Waldemar

 

[Waldemar-Johann]

Wherever there is a place for it to see if room modes define the dip around 80 Hz.

Hello Salt,
I have reconsidered the situation as it stands now and have come to the conclusion that it will stay that way.

All the best and a good start in the week
Waldemar

 

[Waldemar-Johann]

Once again to everyone,
can I use it to take further measurements or are the measurements useless?
Would it be better to order a USB measure microphone like the UMIK-1?

Many thanks for your help and answers.

All the best,
Waldemar

 

[Waldemar-Johann]

Good evening everyone,
so I have completely redone the measurement, I made a mistake here.
I have now measured for the first time.
I look forward to professional feedback and help!

All the best and a great evening,
Waldemar

 

[Keith_W]

If you don't ask a question, there is nothing to answer. What do you want us to look at?

And why does this curve look so strange? (From Jul 15 L+R-1").

 

[Waldemar-Johann]

If you don't ask a question, there is nothing to answer. What do you want us to look at?

View attachment 463452

And why does this curve look so strange? (From Jul 15 L+R-1").

Hello Keith,

thank you for coming back.

My question now is, which treatment should I start first to get an improvement here?

And why does this curve look so strange? (From Jul 15 L+R-1").

I can't understand that right now.
The file is from Jul_15_75dB.mdat.
Then I read again that you should be at least between 80-85dB and that's why I did the measurement with 80dB again, where it doesn't look like that?
To be honest, I still haven't really understood the correlations.
I'm just glad that I've hopefully measured properly now.

All the best,
Waldemar

 

[RandomEar]

@Waldemar-Johann Could you please open a new thread for your troubleshooting? Upload your latest measurements there, describe your problem and feel free to post the link to the new thread here.

 

[Waldemar-Johann]

@Waldemar-Johann Could you please open a new thread for your troubleshooting? Upload your latest measurements there, describe your problem and feel free to post the link to the new thread here.

I will do, no problem.

 

[JD1]

Hello everyone, 3 questions please, but mostly interested in question nr.1:

Setup: I'm using asio driver of focusrite 2i2 gen 3 with output 2 selected as output and timing reference output as output 2 and loopback input as input 2
And input 1 for microphone, when I go to measure or generator I can only select output 2 or 1 (output 2 is right channel and output 1 is left channel) output 1 I don't use, and I have soldered/made a loopback cable from a TRS and another TRS cable that then goes to 2 rca cables (Raw-cat youtube loopback cable).

Question 1: Rew doesn't give me options to select what output 2 sends as signal, and I think, but I'm not sure it has any effect on rew, in windows I can change output to mono by toggling on, mono audio (windows system > sound (choose where to play sound (output) > mono audio.

Rew also allows for secondary output to be selected and you can again select output 2 however this doesn't do anything I think (this way).

So the question is, is the signal being sent is simply right audio to Wiim ultra, to both left and right inputs via rca (line in), for measuring does this work? I mean will the sub out in wiim ultra sum both right signals incoming into wiim line in and play as if receiving right and left? , should I use mono audio? (Would it work given it is windows option, I have selected audio enhancements off in windows for focusrite output/input) would the wiim receiving mono in left and right properly seperate it into left and right stereo? This has me searching Google and everywhere but I can't find the answer, if I play all speakers or mains + subwoofer even if it is uncorrelated since it's giving both left and right channel line in inputs doesn't it become correlated?

Why doesn't rew using asio let the choice of mono or stereo like in java, and if I send L+R using y split will it feed that signal to both left and right so making this useless? I'm confused about this, what is best way to do sweeps and mmm with this asio driver and focusrite given the output 2 limitations. Will subwoofer properly sum the 2 right channels being given? Will the 2 speakers playing only a right channel properly sum?

Question 2: using higher sample rate like 192khz and 256k fft lenght makes the averages way faster, so doesn't this make it superior to 48khz and 64k fft lenght, I mean it does have higher resolution (compared to 48khz the 20hz to 20khz) and is quicker.

So although rew reccomends 48khz and 64k fft lenght isn't 192khz and 256k fft lenght superior given my laptop and focusrite can certainly handle it?

Question 3: buffer size how do I know I need to increase it?

 

[Keith_W]

You are using a Y splitter for output 2 (timing ref) which is where you made your mistake. The idea behind loopback timing measurements is to compare the time between two circuits.

Set up your Focusrite 2i2 like this:

CIRCUIT 1 (Measurement circuit):
OUTPUT 1 ---> to your amp, speakers, etc.
INPUT 1 <--- Microphone

CIRCUIT 2 (Timing reference circuit):
OUTPUT 2 ---> physical loopback cable ---> INPUT 2

Now set up REW like this:

Mode: ASIO
Output device: Focusrite 2i2
Output: OUTPUT 1
Input device: INPUT 1
Timing reference output: R (assuming output 2 = R)
Loopback input: R (assuming input 2 = R)

Question 1: If you are using REW's "measure" function, REW sends a chirp through the loopback reference circuit. I believe it's the same tweeter chirp that is used if you use an acoustic timing reference. Other types of REW measurements allow you to send different signals through the loopback circuit, for e.g. if you use time alignment with wavelets REW will send a wavelet through the loopback timing reference circuit.

Re: measuring through the Wiim Ultra. The problem is, you have only one output from your Focusrite, and two inputs (L/R) on your Wiim Ultra. Your options are (1) measure L and R separately, which will mean recabling between measurements or (2) use your Y splitter from the Focusrite to drive both L/R inputs on the Wiim simultaneously, (3) MAYBE Wiim has a function to mono a single input to L/R, I don't know. I recommend the first option - measure L/R separately.

Re: all the summing questions, I don't know. Those are Wiim questions. Consult your manual or look in your menu.

Re: measuring at higher sample rate. This does not give you higher resolution, this gives you a higher frequency ceiling. For e.g. 48kHz means you can measure up to 24kHz. There is no point going higher than this for acoustic measurements, it is unlikely your microphone can measure that high. Those super-high sample rates are for measuring DAC's and amps.

Re: buffer size. If you don't have any issues with your measurement, don't touch it. You need to increase it if you start getting dropouts or stutter.

 

[JD1]

You are using a Y splitter for output 2 (timing ref) which is where you made your mistake. The idea behind loopback timing measurements is to compare the time between two circuits.

Set up your Focusrite 2i2 like this:

CIRCUIT 1 (Measurement circuit):
OUTPUT 1 ---> to your amp, speakers, etc.
INPUT 1 <--- Microphone

CIRCUIT 2 (Timing reference circuit):
OUTPUT 2 ---> physical loopback cable ---> INPUT 2

Now set up REW like this:

Mode: ASIO
Output device: Focusrite 2i2
Output: OUTPUT 1
Input device: INPUT 1
Timing reference output: R (assuming output 2 = R)
Loopback input: R (assuming input 2 = R)

Question 1: If you are using REW's "measure" function, REW sends a chirp through the loopback reference circuit. I believe it's the same tweeter chirp that is used if you use an acoustic timing reference. Other types of REW measurements allow you to send different signals through the loopback circuit, for e.g. if you use time alignment with wavelets REW will send a wavelet through the loopback timing reference circuit.

Re: measuring through the Wiim Ultra. The problem is, you have only one output from your Focusrite, and two inputs (L/R) on your Wiim Ultra. Your options are (1) measure L and R separately, which will mean recabling between measurements or (2) use your Y splitter from the Focusrite to drive both L/R inputs on the Wiim simultaneously, (3) MAYBE Wiim has a function to mono a single input to L/R, I don't know. I recommend the first option - measure L/R separately.

Re: all the summing questions, I don't know. Those are Wiim questions. Consult your manual or look in your menu.

Re: measuring at higher sample rate. This does not give you higher resolution, this gives you a higher frequency ceiling. For e.g. 48kHz means you can measure up to 24kHz. There is no point going higher than this for acoustic measurements, it is unlikely your microphone can measure that high. Those super-high sample rates are for measuring DAC's and amps.

Re: buffer size. If you don't have any issues with your measurement, don't touch it. You need to increase it if you start getting dropouts or stutter.

The loopback cable is working, that's not the issue, I get consistent impulse responses.

My question is, more about java allowing to send through one output L+R signals and asio not allowing that, assuming that output is Y split doesn't the receiver then split L and right from L+R signal?

My question is more about summing if output sends R signal Y split into left and right channel. And I play with speakers like that or a speaker plus sub. I mean for MMM I can simply use USB on wiim ultra and play L+R signal from rew generated pink noise. But using output 2 Y split would be easier.

And I guess playing right channel on left speaker or right speaker individually is the same as sending left to left and right to right.

My question in this regard is more about sub, if I send R + R does it not sum properly (using sub out) and play lower volume?

If I send mono Y split does it play louder than supposed too since it's summing two mono signals?

 

[Keith_W]

I have no idea what you are talking about. Cable up your measurement system the way I described, and it will work.

 

[JD1]

Ok maybe I should've googled this sooner:

Coherent vs. Incoherent Signals:
In audio, coherence refers to the relationship between two signals.
Coherent (or correlated) signals: Have the same waveform and are in phase, leading to a +6dB gain when summed.
Incoherent (or uncorrelated) signals: Have different waveforms and are not in phase, leading to a +3dB gain when summed.


And a another post in a forum

"
I'm asking because if you EQ left and right channels each individually to the B&K target, it is expected that the summed L+R response will be about 3dB higher in the bass range.

In my experience the two channels will sum as incoherent sound sources at high frequencies (i.e. +3dB compared to individual channel level) and as coherent sound sources at low frequencies (i.e. +6dB compared to individual channel level).
The difference is usually the biggest below about 200Hz, which to me looks exactly like what your measurements seem to show.

So if you use the "stereo" RC variant I would expect the summed L+R measurement to match the B&K curve well, but if you use the individual channel RC variant I'd expect the summed L+R measurement to overshoot the B&K curve by about 3dB below 200Hz or so."

 

[JD1]

You are using a Y splitter for output 2 (timing ref) which is where you made your mistake. The idea behind loopback timing measurements is to compare the time between two circuits.

Set up your Focusrite 2i2 like this:

CIRCUIT 1 (Measurement circuit):
OUTPUT 1 ---> to your amp, speakers, etc.
INPUT 1 <--- Microphone

CIRCUIT 2 (Timing reference circuit):
OUTPUT 2 ---> physical loopback cable ---> INPUT 2

Now set up REW like this:

Mode: ASIO
Output device: Focusrite 2i2
Output: OUTPUT 1
Input device: INPUT 1
Timing reference output: R (assuming output 2 = R)
Loopback input: R (assuming input 2 = R)

Question 1: If you are using REW's "measure" function, REW sends a chirp through the loopback reference circuit. I believe it's the same tweeter chirp that is used if you use an acoustic timing reference. Other types of REW measurements allow you to send different signals through the loopback circuit, for e.g. if you use time alignment with wavelets REW will send a wavelet through the loopback timing reference circuit.

Re: measuring through the Wiim Ultra. The problem is, you have only one output from your Focusrite, and two inputs (L/R) on your Wiim Ultra. Your options are (1) measure L and R separately, which will mean recabling between measurements or (2) use your Y splitter from the Focusrite to drive both L/R inputs on the Wiim simultaneously, (3) MAYBE Wiim has a function to mono a single input to L/R, I don't know. I recommend the first option - measure L/R separately.

Re: all the summing questions, I don't know. Those are Wiim questions. Consult your manual or look in your menu.

Re: measuring at higher sample rate. This does not give you higher resolution, this gives you a higher frequency ceiling. For e.g. 48kHz means you can measure up to 24kHz. There is no point going higher than this for acoustic measurements, it is unlikely your microphone can measure that high. Those super-high sample rates are for measuring DAC's and amps.

Re: buffer size. If you don't have any issues with your measurement, don't touch it. You need to increase it if you start getting dropouts or stutter.

The y split I'm talking about is a double y split (soldered) it is TRS connected to main cable and another TRS also connected to main cable (and the previous trs) then the main cable on the other end has 2 rcas.

So 1 TRS is in output 2 the other TRS goes to input 2, and the RCAs go into left and right channel in wiim ultra.

So I'm basically already doing "(2) use your Y splitter from the Focusrite to drive both L/R inputs on the Wiim simultaneously"

My questions are if I'm sending 2 uncorrelated (which I guess became correlated) to left/right is it a mono signal? And wil since wiim ultra sums L/R for subout is the signal acting as a mono?

I already ordered another TRS to RCA so I plan on connecting output 1 to left channel and test what's the difference. And if I can get a true uncorrelated signal or if I was already getting it or a correlated signal since L/R is both receiving it at same time, and if wiim is summing it for subwoofer. Basically what are the differences is what I will test.

Another question is with rew and focusrite how to send a mono signal.