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Discussion Starter #1
Hi there. I'm just starting out with REW and have just attempted to calibrate the sound card in my Mac Pro (mid 2010 running 10.7.5). The sound card calibration produced the following:



while the result of a measurement with the cal file in place is shown below:



I wanted to check the results as, while the variance is for the most part within +/- 0.1 db it would appear to have a lot more variance than the example depicted in the help files.

Have I made my first tentative steps correctly?

Thanks in advance

Steve
 

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It's probably fine, onboard soundcards aren't particularly great in general. For example, the heavy LF roll off that you can see in your calibration. The more that needs compensated for with the cal the more noise in the sound device is getting amplified... You'd get better measurement results from an external/better soundcard.
 

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Discussion Starter #3
Thanks. One more basic question at this stage... Am I right in understanding that the basic setup for REW is to analyse one channel at a time or do people typically use a splitter and run stereo for their analyses?
 

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Yeah it is nice to be able to measure L, R, and L+R if that's what you're asking. It shouldn't be hard to come up with a way to send output to one channel at a time.
 

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Discussion Starter #5
Thanks. One of the bigger issues I face at the moment is that I don't have a laptop. Lugging a Mac Pro and display around to run tests isn't fun. I presume I will be able to set things up, capture all the measurements, return everything to my desk and then analyse at my leisure.
 

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Thanks. One of the bigger issues I face at the moment is that I don't have a laptop. Lugging a Mac Pro and display around to run tests isn't fun. I presume I will be able to set things up, capture all the measurements, return everything to my desk and then analyse at my leisure.
That's the theory, except when you forget a measurement, or decide you want to re-do a measurement just a little bit differently. It IS a pain lugging a desktop computer around.
 

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Discussion Starter #7 (Edited)
I can imagine.

There's one other thing I'd like to check at the moment. (FYI I am using a Behringer ECM8000 microphone and an Avid Recording Studio by M-Audio, powered by USB and connected to my Mac via its right line out to my line in at the rear of my Mac.)

I see I need to use another SPL to calibrate the SPL function in REW. (At the moment the dB levels measured are very low.) The only SPL I have is the Studio Six Digital SPL app on my iPhone. Is this good enough? I also presume that the Mic Gain on the M-Audio Avid needs to always be at the same level. Should I use zero? What about Output control on the Avid - leave at zero always also? (I see that the input level for the Line In (audio line-in port) on the Mac (set in System Prefs-> Sound) also always needs to be at the same level as when SPL was calibrated. When I did the calibration of my sound card, I found that I had to set the input level for the Line In (Audio Line-in Port) to maximum and also raise the Line Out level to reach -12dB.)

Apologies for the string of questions.

Steve
 

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Nothing wrong with using the SPL app. Set your mic gain to whatever is needed to get a decent signal level, if you alter the gain setting just repeat the REW SPL calibration. Doesn't matter too much which output control you use to adjust the output level (REW, Avid, ...), but simpler to stick with one.
 

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Discussion Starter #9
I am struggling with Check Levels. I generate a test signal, either sub or main, but even with the mic gain on maximum on the M-Audio and with line input volume set to maximum I can only get the input level in REW to -43dB. Also, the gain control affects the Left channel in REW even though everything is cabled for the right only (and right is set in REW prefs). I must have a bad cable?
 

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-43dB is still useable depending on the level when the test signal is not playing - what are the levels when the input is silent?

What levels are you seeing on the unused channel?

Make sure the 'Thru' box is not ticked for the line in.
 

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Discussion Starter #11
Replaced cable. I think the one I was using has the left right mixed between mini-plug and composite ends. Now have right channel responding.

According to my SSD SPL, my room measures approximately 37.4 with nothing playing.

I calibrated REW's SPL with pink noise measuring 75.3. Opening SPL Meter in REW it reads circa 73 with nothing playing and input -40 ish.

When I run Check Levels, I see -12dB on the input meter, -61ish on left and -43/44 ish (it bounces around a lot) for the right.

I am using the sound card calibration i did earlier and I downloaded the calibration file for the ECM8000 from this website.

I don't see a Thru box anywhere.

For the output device selection I have Default Device (the only other option is Java Sound Device) and for Input Device I have selected Built In Line Input.
 

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From your description it doesn't sound like the input level changes whether you have a test signal playing or not? For setup it is better to set the built-in line input as your default input in Audio/Midi prefs and set REW to 'Default input'.
 

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Discussion Starter #13
In System Prefs -> Sound my input is set to Line In and output set to Line Out. If I open Audio Midi Setup I see these as active. (I can not control the master volume from Audio Midi Setup.)

If I set REW's input device to default device everything is the same.

When I Check Levels, adjusting the mic gain alters the right level. When I open SPL Meter, calibrate it, its level does not drop when the pink noise ends - it also doesn't read anything like the SSD SPL (even after calibration).

Thanks for the help
 

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Discussion Starter #15
Ok, I don't know why but things seem more normal now. I decided to test the mic by simply plugging the output of the M-Audio pre-amp directly into my Theta. After a little puffing on the mic and switching inputs on the Theta (and then back to the original one) I could hear my voice out the speakers. Reconnected to the computer and things are very different from before. I can achieve -18dB on the right channel without having the input volume set to its maximum. I now have a very high degree of confidence in this mic and pre-amp. Not.
 

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Ok, I don't know why but things seem more normal now. I decided to test the mic by simply plugging the output of the M-Audio pre-amp directly into my Theta. After a little puffing on the mic and switching inputs on the Theta (and then back to the original one) I could hear my voice out the speakers. Reconnected to the computer and things are very different from before. I can achieve -18dB on the right channel without having the input volume set to its maximum. I now have a very high degree of confidence in this mic and pre-amp. Not.
Chalk it up to "user-error" and the "learning experience" ( or the "Way We Learn" ) . :T

On a different note;

- Do you realize that you should be able to use your M-Audio soundcard to inject signal directly into the computer & therefore REW, avoiding your current kludge ??
- ( ie; this would do away with your current scheme of only using the M-Audio for it's pre-amp section where you then cascade signal into the Mac's soundcard )

- So far, I don't see any stated reason to use the Macs soundcard in your setup ( I assume it comes with its own "Core Audio" drivers, yes / no ???? ) .


:sn:
 

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Discussion Starter #18
No, I'm not sure what you mean. I've been just following the instructions so far.

(After "testing" the mic I returned the cabling to the way it was before (i.e. as per the REW help guide). This is why I have no idea why things should now work when they didn't before. Mic to Avid->Right channel to computer audio in + computer audio out to analog in on the Theta.)

The "Avid Recording Studio" comes with Pro Tools SE recording software and presumably any relevant drivers. This is what I have:

http://www.amazon.co.uk/dp/B0041OSWUG/?tag=hydra0b-21&hvadid=9550933629&ref=asc_df_B0041OSWUG
 

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Discussion Starter #20 (Edited)
Just to clarify the point I made above, I could not hear anything through the speakers from the mic when it was set up to measure. I wanted to see if the mic actually worked and so to test that I connected the analog output of the Avid to my Theta. I then returned the cabling to follow the REW online instructions.

i used 1M, 4 sweeps when measuring (although I only ever heard two per measurement).
 
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