REW Input

[Glenn Kuras]

not totally following what you did but the following video shows you how to calibrate. BTW you really do not have to calibrate to get a good reading. So if you have can't make it work then skip it for now.
Room EQ Wizard Tutorial Video

[Rondeath]

hi glenn,
i will try without calibration. I saw your video and follow exactly as it says. At 2:20 you can see 2 meters. One for out and one for left. In my pc, just appear the the Out meter at -12dbFS. Nothing happen with the left or right meter.

In my interface I have to remove all the cables and put only the loopback cable correct?

thanks for the reply glenn

Edit: Glenn, if i remove the loopback cable, and return to the speakers and mic to the interface, now the signals appear in the left/right meter.
But if i try to measure without calibration soundcard, the soft said that i have lower level for measure.

WHen i do the calibration, i really need to remove everything from interface? (like speakers/mics....). Only plug the loopback cable?

[Rondeath]

Edit: i got it now, but i dont know if its correct.
http://s18.postimage.org/cybhmi795/C...tion_Curve.jpg

Glenn, in your video, after do this calibration, in the check level part, i need to do with the loopback cable or with the speaker/mic plugged?

[Glenn Kuras]

When you are checking the level you just have the mic plugged in, if I am understanding you correctly. Once you test post the REW file (zipped) and I can check it out.

[Ethan Winer]

Originally Posted by Rondeath

i will try without calibration.

I got your PM. I never bother with calibration because all that really matters is the relative levels and ringing etc. Calibration was (possibly) needed years ago, but all modern sounds cards are flat enough to ignore any errors they add.

--Ethan

The Acoustic Treatment Experts

[Rondeath]

thanks, thanks ... so I must just remove the soundcard calibration file(generated by this graph above) and remove the file Generic calibration mic?

[JohnPM]

Doing the loopback calibration when setting up REW is more about making sure the setup works (and there is no monitoring/feedback) than needing to calibrate the soundcard, since most are pretty flat. It is much easier to spot an invalid measurement when you are just measuring a piece of wire - avoids the frustration of making changes to try and fix things in what you think is a room measurement, but later turns out to be just noise or garbled by an error in the setup.

[Ethan Winer]

^^^ Good point John. My setup is stable and connected properly, so that's not a concern for me. But I get your point.

--Ethan

[Rondeath]

Thanks all for the support guys.
Let me know one thing, Im tryin to check levels, but to get 75dbSPL with pink noise (with REW SPL Meter and ECM), volumes are already extremely high at about 65dbSPL.
Its correct?

[jrhager84]

Originally Posted by Rondeath

Thanks all for the support guys.
Let me know one thing, Im tryin to check levels, but to get 75dbSPL with pink noise (with REW SPL Meter and ECM), volumes are already extremely high at about 65dbSPL.
Its correct?

What weight are you using? I believe REW calls for a slow, C-weighted meter.

Sent from my SAMSUNG-SGH-I777 using Tapatalk

[Ethan Winer]

Originally Posted by jrhager84

I believe REW calls for a slow, C-weighted meter.

REW works best with a microphone that's flat. Weighting curves in SPL meters affect the meter readings, but (I don't think) they affect what comes out the RCA output jack.

--Ethan

[jrhager84]

Originally Posted by Ethan Winer

REW works best with a microphone that's flat. Weighting curves in SPL meters affect the meter readings, but (I don't think) they affect what comes out the RCA output jack.

--Ethan

Right. If he's using different weighting, he'll get wrong dB values, which if why it's really loud at only '65dB' measured. He was compensating with gain. That's the only reason I brought it up.

Sent from my SAMSUNG-SGH-I777 using Tapatalk

[DanDan]

Reference levels can be very confusing.
The SPL meter in REW is dependent on soundcard and mic preamp gain.
Play pink noise in the room. Measure using a real SLM, at the mix or measurement mic position. Turn up the speakers until the SLM reads 75dBSPL C Slow. Mark the volume control position! Adjust the SPL Meter in REW to read the same 75 ( with C and Slow weighings engaged).
Now the SPL graphs in REW will read real SPL numbers.
Using cheap SLM's as measurement mics has caused oodles of trouble.
Many of them have poor frequency response and lots of noise.
Some even put out DC leakage on the line out.....
I recommend the Dayton measuring mic which is cheap and comes with a Mic Cal file. You don't need to own an SLM, although they are very useful in general. You could just borrow one and Cal your REW, gain, and speaker Volume settings. They won't drift significantly for a long time.

DD

[Rondeath]

Thanks for the support guys. Now I think it worked.
I have not used the soundcard calibration file, and not used generic calibration mic file(ECM8000)
So, to check levels with both speakers, i just put the mic at listening position, exactly on the symmetry line of the room, pointing upwards(to the celling).
Click at check levels in preferences and use SPL Meter in REW and ECM8000 to calibrate. I read ~75bSPLoutput and ~18dbFSinput, turn a little down the sine sweep and got green headroom. Finally, i got the graphics.

Second, to measure the room with one spakers(after measure the room with both), I do not let the microphone line in the height of equilateral triangle imaginary, Now I do a rotation of a mic for the tweeter point to the microphone (still pointing the mic at the ceiling), check levels again and do the measure. Finally, i got the graphcs.

http://postimage.org/image/mpnxg61up/ (with mic pointing to the celling)
Am I right?
Thanks so much again everyone that help me.
Best for all

[DanDan]

The SPL meter in REW needs to be compared/calibrated to a real SLM.
Why point the mic at the ceiling? Do you point the speakers at the ceiling?
DD

[Rondeath]

Hi DanDan, I thought if rew was accepting that level of input and output and headroom was OK,the measurement would be OK.
When i say SLM = SPL Meter? If yes, i have one http://diyaudioprojects.com/Testeq/R...50/33-2050.jpg -> SO its better use this for check levels?

and about pointing the mic at the ceiling, I use it horizontally.

I took this idea from RealTraps.com
"Most room measurements are done with the microphone at the listening position, at ear height, and pointing straight up to not favor either speaker."

what I did wrong?

Thanks DanDan

[Ethan Winer]

Originally Posted by DanDan

Why point the mic at the ceiling? Do you point the speakers at the ceiling?

Pointing up is needed when you're using an SPL meter to balance the levels between two or more speakers. I suppose for stereo you could point it straight ahead, so the off-axis angle is the same for the left and right speakers. But for a surround system, it really needs to be pointed up.

--Ethan

[Rondeath]

Ethan, i just a little confusing. about my process I used to measure, what was wrong?
thanks so much all

[DanDan]

Most room measurements are done with the microphone at the listening position, at ear height, and pointing straight up to not favor either speaker

Ethan, I think that is bound to cause confusion because it ain't a fact. Maybe worth a revision?
Pointing a mic upwards means it is measuring off axis. This is fine if the mic and or calibration file were designed that way. Mics in US SLM's are such.
But not in SLM's in other countries. Most mics sold using the term 'measurement' are Direct Field mics. They are designed to be pointed at the source of interest. Many have poor or unknown response off axis.
The Cal files that come with say the Dayton, are done on axis.

Pointing upwards is indeed a convenient way of level checking surround speakers. But all other room measurements are best performed using the equipment as per the manufacturers design intentions.

Ron, by all means have the mic equidistant from both speakers and point it equally towards them, or equally away from them. If you are measuring Level. Pointing forward exactly between the two will be fine for Frequency Response, ETC, Waterfalls, and so on. Personally I use two different mic locations, where the ears are, and point the mic directly at each speaker.
I think this is a tad more realistic than measuring what the nose hears!

Use your SLM and your volume control to establish a pink noise level in the room.
Say 75dB SPL C S. Mark the position of the volume control. Then adjust your mic preamp and the SPL meter in REW to read the same figure. Now you can put away the SLM because REW will do the same job.


DD

[Rondeath]

DanDan, thanks thanks so much,
when you said:
"Personally I use two different mic locations, where the ears are, and point the mic directly at each speaker.
I think this is a tad more realistic than measuring what the nose hears! "

That is to measure the room with only one of the speakers(right and then left separately). when measuring with the two connected, put in the middle of the head and point to the middle of the speakers correct?

[DanDan]

You are welcome Ron.
The single and dual speaker thing is another source of much confusion.
My view is that single speaker measurement is the norm.
The software we use can combine the measurements.
One might drive two now and again to see if any surprises, but I would leave the mic in an ear position.

Our measurement processes are not done to a standard so there is no correct way. I find it best to measure with a purpose. e.g. stimulate the modes fully and receive them fully by placing a speaker in a floor corner, the mic in the opposing ceiling corner. If you are setting simple multichannel level then Ethan's 'point the mic equally away from all speakers is a nice tip.

Sometimes I focus on two ear spots. Sometimes I will do 8 or more locations within the required listening area.
Quite a lot of the time I am looking at the difference caused by moving a mic or speaker position. I like to call that 'interrogating the room'.

But the simple go-to, one speaker, point the mic at the tweeter.


DD

[Ethan Winer]

Originally Posted by DanDan

Pointing upwards is indeed a convenient way of level checking surround speakers.

I think that's what I said.

But pointing up is also fine for level-balancing stereo speakers. You are correct that for the most accurate response at very high frequencies the microphone should point at the loudspeaker.

--Ethan

[Ethan Winer]

Originally Posted by Rondeath

Ethan, i just a little confusing. about my process I used to measure, what was wrong?

I have several posts in this thread. What part are you unsure about?

--Ethan

[Rondeath]

Dandan, thanks again dude
Ethan, im so sorry for my noobness >(
thanks to everyone who had patience with me e
I guess now I could make the measurement.
My room is practically empty, just have my equipment and a bed.
i made 3 measure and use overlay to compare.

View image: overlay 2

looking well, what would be the best graphic?

[Ethan Winer]

Originally Posted by Rondeath

what would be the best graphic?

The one that's closest to a straight horizontal line.

--Ethan