# Weird REW Soundcard Calibration Results



## TheChemistTree (Jan 27, 2012)

Hi There,

I am in the process of building a studio control room for mixing music on our flat.

The room itself has terrible acoustics so i was advised to download and use the REW software.

On reading through the instructions i first set about calibrating my soundcard. I have a MOTU 828mkII.

I followed the instructions and set the input and output to the defaults that i had set windows to use. I then calibrated by going step by step through the calibration process. I tried it 3 times and had different results (the soundcard reading stayed the same but the phasing changed). The 3rd result is here as uploaded.

What is confusing me though is that it says in the pane on the left is that there was no device selected. When i was asked to set the input/output levels it was clearly using the soundcard, as the gain dial on the input path was working and the soundcard's mixer was showing the reading from the sound generated by the software.

Also it says to check this was successful by unchecking the SPL option in the next page of the preferences menu, and when i went over to this it was already unchecked, so i went back and pressed the measure button and it said that the SPL meter had not been calibrated. How do i go about doing this also?

Many thanks in advance,

TCT.


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## fusseli (May 1, 2007)

That cal looks pretty typical for a soundcard to me, I don't think anythign is wrong with it. Did you click "Make Cal..." button after? That's where you save it as a .cal and REW loads it as your calibration file. I wouldn't worry about the no output device selected, I just redid my soundcard cal to check and mine shows the same thing as yours.

You will need to find a .cal file for your microphone. What mic are you using?

You also need to calibrate the SPL level using an SPL meter, so that your measurements on the graph line up with the dB measurements you are actually hearing in-room.


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## TheChemistTree (Jan 27, 2012)

Hi Fusseli,

Thanks a lot for the reply.

I will be using a Rode NT1.A (or i can use an SM57 or a 58 Beta should they be better for this?). I haven't yet plugged it in, all i have done so far is created the loop on the soundcard and calibrated it. I did save the calibraton using the save icon in the left pane (next to where it says about no output selected).

As for the SPL meter, i don't own one of those. I thought that the REW software had one built in and i wouldn't need to get one. Should i invest in one or can the software do all of this?

Thanks for your help,

TCT


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## SAC (Dec 3, 2009)

The mic must be an omni-directional mic.

You might want to pick up a calibrated Behringer ECM8000 or a Dayton (Superlux) EMM6 measurement mic.

You only need an SPL meter if you are trying to set the levels relative to another source. Otherwise the levels will be relative to one another as made on the platform, which is sufficient for the vast majority of applications.


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## BP1Fanatic (Mar 28, 2011)

My 1st post! What am I doing wrong? I keep getting variations from 108db to 140db when I try to calibrate the sound card. It's Realtek HD Audio, XP, Eee PC.


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## fusseli (May 1, 2007)

BP1Fanatic said:


> My 1st post! What am I doing wrong? I keep getting variations from 108db to 140db when I try to calibrate the sound card. It's Realtek HD Audio, XP, Eee PC.


You will need to start your own thread and clearly state what problems you are having and your measurement setup, including what exact equipment you are using. Good luck and welcome to HTS!


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## TheChemistTree (Jan 27, 2012)

Hi Guys,

Ok i now am the proud owner of a Behringer ECM8000.

My soundcard is now calibrated. I have moved on to the check levels part of the .pdf file. It says that i must use a SPL meter and set it to i think it was 75 db.

Is this achieved by using the mic and the spl meter in the REW software as i do not own an SPL meter?

Thanks again in advance,

TCT


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## EarlK (Jan 1, 2010)

> Is this achieved by using the mic and the spl meter in the REW software as i do not own an SPL meter?


 
No, your test mic &/or your pre-amp don't know how loud things are / think about it / only a real SPL Meter comes calibrated to some form of relative "loudness" . To truly set SPL levels so that REW knows how loud the source is / you need an SPL Meter .

OTOH, one can operate REW without calibrating the SPL meter function , but it's easier on everybody if one does ( even if one needs to make up a number within the calibration procedure ) . 

> If you don't have an SLM ( Sound Level Meter ) simply set your playback/test level up to the point ( using Pink Noise ) where the level impedes normal conversation ( at the point where your test mic will be ) .

> Use this level as your 75db reference level.

> ( ie; You still go through REWs SPL meter calibration routine, but when you think it's loud enough to be 75db , you then enter , 75db into the calibration window & hit "Done" ( or whatever the button actually says ) .

> Now you'll at least have a reasonable point of reference for how loud things are ( give or take 5db ) .

:sn:


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## TheChemistTree (Jan 27, 2012)

Thanks for the reply.

I know that my microphone cannot determine the sound level, so i was wondering whether i could use the SPL meter in REW 5 to find out the 75 dB level by generating the pink noise in REW, and using the mic to capture the pink noise, and then using the SPL in REW to determine how loud it is.

If not, is does anyone know of any other software out there that would be able to do this, as my budget won't run to a meter as i have spent it on the mic 

Thanks in advance guys.

TCT


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## SAC (Dec 3, 2009)

TheChemistTree said:


> I know that my microphone cannot determine the sound level, so i was wondering whether i could use the SPL meter in REW 5 to find out the 75 dB level by generating the pink noise in REW, and using the mic to capture the pink noise, and then using the SPL in REW to determine how loud it is.
> 
> If not, is does anyone know of any other software out there that would be able to do this, as my budget won't run to a meter as i have spent it on the mic


Think about the circular nature of what you are suggesting.

You are proposing the use of an uncalibrated source in REW to arbitrarily set the level so that you can then turn around and using that level, arbitrarily assign and 'calibrate' REW to 75 dB....

All sounds great, except that the signal level that REW generates initially that you propose using for a reference has no necessary relationship to 75 dB.

Follow what EarlK has already suggested above in order to establish a workable level in lieu of an SPL meter...


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## Wayne A. Pflughaupt (Apr 13, 2006)

TheChemistTree said:


> I know that my microphone cannot determine the sound level, so i was wondering whether i could use the SPL meter in REW 5 to find out the 75 dB level by generating the pink noise in REW, and using the mic to capture the pink noise, and then using the SPL in REW to determine how loud it is.


Look at it this way: REW does not know “where” 75 dB is, nor does it have the means to automatically determine that. The purpose of the SPL calibration routine is to “tell” REW “where” 75 dB is. That way when you take a frequency response measurement, the graph’s vertical dB markings are meaningful. Otherwise, they’re arbitrary. Make sense?

As Earl noted, you can take measurements without the SPL calibration. As long as your signal level isn’t too low, or so high that it’s clipping, you can get a useable measurement.

Regards,
Wayne


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## TheChemistTree (Jan 27, 2012)

Hi Guys,

Thanks for the help.

What i managed to do is get a SPL meter phone app on my friends phone (this i only used to find the 75db point). I am guessing that these apps are not amazingly accurate but at least it gave me a rough idea.

I have now tested my room.

Thanks again guys :clap:,

TCT


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