Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 56

Quote:

Originally Posted by kbarnes701 

Whatever John does, I do hope that most of us, in this thread at least, will be making a donation.

I was impressed enough with the software (even though I couldn't use it much) that I made a donation my first time around. Now, with a EMM-6 on its way, I think there should be a way of donating to THIS project.

Michael

Quote:

Originally Posted by AV_mike 

Quote:

Originally Posted by JohnPM 

Hello all,

To add support for UMM-6 in REW I need to know how the Windows input volume setting affects the levels coming from the mic, anyone fancy helping with that? It 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 the UMM-6 -> 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 you have the patience to write down, 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

Ideally I need that info from Windows XP, Windows 7 and Windows 8 as they differ in how they handle level settings. An extra handy bit of info would be the Windows volume control dB readings with the slider at each end of the scale, which can be obtained (on Win 8 at least, I'm guessing Win7 also) by right clicking the volume slider and selecting the decibels option.

Could also do with getting the same info for an Omnimic used on Win 8 (I already have Win 7 data for that).

Hi JohnPM,

Here is some Windows 7 data, as requested. Can't help with Win 8, may be able to do Win XP later.

Data as follows:-
First column = Windows 7 Level control setting within Control Panel
Second column = Reading taken from REW SPL meter (just below A/C/Z button)
Third column = REW levels did not change for every Windows 7 control adjustment, so this column lists the values at which a change occurred, as the values were decreased. This is why some REW values remain unchanged in the first two columns.

100 -18.7 99
95 -20.1 87
90 -20.0 77
85 -21.4 67
80 -21.4 58
75 -22.7 51
70 -22.7 44
65 -24.1 38
60 -24.1 33
55 -25.5 28
50 -28.1 24
45 -28.1 20
40 -29.4 16
35 -30.7 13
30 -32.0 11
25 -33.4 8
20 -36.1 6
15 -37.5 4
10 -41.2 2
5 -43.9 1
0 -48.0

Independent SPL meter read 99.2dB
Win7 Level slider range was 0.0dB to +20.0dB

Regards, Mike.

Edit, tried to respace the data, but extra spaces keep disappearing, sorry.

Mike, something seems to be wrong with your data.  Looking at John's instructions, he says to place the SPL in the same spot, vary the mic level, and read the SPL level.  Your SPL measurements go all the way down to zero.  I know for a fact that the SPL meter always measures at least the noise floor of your listening room which, if like a typical rooom, is around 40dB.  So how can you be seeing a SPL reading of zero?

Perhaps I am not interpreting John's instructions correctly.

I'm still not understanding, Mike.  Are you saying you are connecting the SPL to REW using the laptop's microphone-in jack?  If yes, did you calibrate the SPL?  Did you use the SPL calibration file as well?

Unfortunately, John's instructions were not very clear.

Quote:

Originally Posted by JohnPM 

Quote:

Originally Posted by kbarnes701 

I have been using REW now for a few weeks and I am loving it. I wanted to make a donation to you as some way of saying 'thank you'. I went to the HTS website but when I go to make a donation, it seems as if the donation is going to HTS rather than to you. Is there something I am missing, or is that the way to do it?

Yes, that's the way to do it (why do I suddenly sound like Punch?).

Thanks John :)  Then that is how I shall do it this very day. Thanks you for all your hard work on REW. It is staggeringly good.

Quote:

Originally Posted by Pres2play 

Can someone explain what the Meter is showing? Which window shows the actual noise floor? Why is the SPL window on top moving without any measurements being taken?

The big window shows the noise floor, or indeed anything that the mic can pick up. The figures in the big window will always show something, if the mic is plugged in, because there is always some background noise present. It fluctuates a little because the noise it is detecting also fluctuates a little.

Quote:

Originally Posted by Pres2play 

Are you sure that's not some headroom number in the big window? I thought the room was quiet when I took that reading. 50 dBs looks good to me now.

Yes I'm sure.

Quote:

Originally Posted by Pres2play 

Can someone explain what the Meter is showing? Which window shows the actual noise floor? Why is the SPL window on top moving without any measurements being taken?

Assuming that you have properly calibrated the mic, and also assuming that the screen shot was taken in a "quiet" room, then the 70.6 reading is indeed your noise floor.  This seems high to me.  One possibility is that the calibration was not done correctly.  Another possibility is that your SPL meter isn't working properly (what make/model do you have?), or that your laptop's internal circuitry is "noisy".  A third possibility is a low frequency noise that isn't readily audible, but is being picked up by the mic (i.e. the noise floor really is 70dB).

Let's quickly review the calibration procedure:

- Place the tip of the SPL at the same place as you would place the UMM-6 (ear height at the ML), pointed at the ceiling, set to C weighting, slow response.  Make sure the battery is OK.

- Generate the calibration test tone (I use the sub tone, the other one is OK as well).

- Watching the SPL meter, adjust the master volume on your AVR until the SPL is reading the desired output level (I use 80dB, which on my AVR is a MV setting of -14).

- Now replace the SPL with the UMM-6, with its tip in exactly the same spot.

- With the calibration tone still playing, and the AVR MV still at the same value, enter the SPL reading you had on the SPL meter (80dB in my case) into the SPL Calibration Reading box, and click Finish.  The UMM-6 is now calibrated.

- To test the calibration, click Calibrate again so the test tone is playing, move the input box out of the way, and observe the reading on the REW SPL--it should be fluctuating right around the value you entered in the previous step (80dB in my case).

Now let's test for low frequency noise in your room:

With the microphone in place at ear level at the MLP, open the real time analyzer (RTA) in REW.  Adjust the graph limits to show 15-20,000, lower limit 0 and upper limit 100.  Click the red button to start the RTA display.  You should see something like this:

If there is indeed a 70dB noise floor in your listening area, then you should be seeing spikes that reach the 70dB level.  In the example above, my noise floor is showing to be about 50dB.  Notice those annoying spikes starting at 1kHz, which are caused by the electronics of the mic or USB interface, a topic of discussion a number of pages back.  Also note that the noise floor is being caused by something around 10Hz, which is inaudible.

Please re-calibrate the mic, perform the RTA measurement, and report the results.

Is there anything in this discussion that needs to be added to the Guide?

Quote:

Originally Posted by AustinJerry 

Is there anything in this discussion that needs to be added to the Guide?

Perhaps only that little bit of marginally useful info after "Now let's test for low frequency noise in your room:"