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Calibrating my home recording studio

1K views 7 replies 4 participants last post by  Wayne A. Pflughaupt 
#1 ·
Dear hometheatershack community,
I'm a home recording musician from Germany and got the following equipment for mixing:

Notebook: Asus X52DE
Power Amplifier: Sony TA-F470
Speakers: JBL Control 5

I usually use the un-eq-ed output from my notebook, plug it into the AUX IN from the power amp and this signal goes straight to the JBL Control 5 speakers. First, I had some EQ and the LOUDNESS switch turned on (at the power amp). But then I realized, those things have to be turned off because I'm mixing music, so it has to be the "real sound" (linear). But when I did this, the sound became very weak in the bass frequencies. So I bought a Behringer ECM8000 and downloaded the REW from this site to start measuring and then correct the frequency responses by adding EQ filters via APO EQ. But you gotta have 2 calibrations for measuring, one for the mic (already got the file) and one for the soundcard/anything between LINE IN and LINE OUT.

So I've got a Behringer Eurorack UB802 mixer and built up a calibration loop like this:

Notebook Line Out -> Sony Power Amp aux in -> right speaker output -> Behringer mixer right line in input -> back to the notebook input

When I now try to calibrate this signal chain, I can't get the amplitudes of IN and OUT equal. IN is very weak, no matter what I do (if i turn it very loud there is a bit more input but the behringer mixer is already clipping). Also tried to record this input to hear what it sounds like, but also got a very weak white noise. I think this could be because of the microphone input from my notebook. I read that I have to use a USB interface for it, if I just have a microphone input and no line input (but I can't say if it is a "pure" microphone input). Maybe the notebook's microphone IN and line OUT can't function simultaniously?

Could that be the problem?

Anyway, is it necessary at all to calibrate my power amp as well or do I just need to calibrate the soundcard itself? I just can't tell if the power amp does something bad to the frequency responses.

Thanks for your help in advance.
 
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#2 · (Edited)
It's my understanding a notebook "line in" or "microphone in" jack is not sufficient for taking these measurements, but considering you are running through a mixer, it may work.

One thing in your loop back config which I would strongly recommend you do not do, is connect the power amp output to the mixer's input.

To create a sound card calibration file, you should:

Notebook Line Out -> Eurorack UB802 Mic input and then Eurorack UB802 output -> Notebook Mic input

Although like I said, I don't know if the notebook's mic input is sufficient for this purpose.
 
#3 ·
Welcome to the Forum, bullonparade!

REW requires a USB sound card or USB mic. You don’t seem to have either of these so unfortunately most of your questions are moot.

That said, the sound card calibration is only needed for low-priced outboard USB sound cards (think Soundblaster and the like), which may not have linear response. It’s not necessary for a good-quality sound card, and it’s not necessary to include every piece of equipment in the loop, unless you suspect it might not have linear response. However it might be good to include the UB802 in the loop (if you ultimately end up using it), just in case the center detents of the tone controls aren’t truly centered (flat).

Also, the calibration file for the ECM8000 you downloaded is generic. Did you notice the graphs on the page where you downloaded, showing the significant variation in response from one ECM8000 sample to the next? Needless to say you don’t want to do any speaker EQing based on a graph that generated from a mic that in all likelihood will not be accurate.

Regards,
Wayne
 
#4 ·
I agree with Wayne, that you should get a quality USB sound card, or mic, instead of trying to use the integrated sound card.

Although the integrated sound card will take measurements, I'm not sure how accurate they will be. Just for the fun of it, I opened up REW on my laptop and chose the JAVA drivers, and then chose the integrated MIC and speakers for the devices. I was able to adjust the levels with the windows controls, and actually take a measurement from the integrated mic playing the test sweep from the integrated speakers. So this leads me to believe you can use the mic/line input on the laptop, although as already stated, it may not be sufficient to get accurate readings.

Wayne,
Is there some other reasoning to saying REW requires a USB mic or sound card, other than the low quality of the integrated sound card's input/mic channel?
 
#6 ·
Wayne,
Is there some other reasoning to saying REW requires a USB mic or sound card...
Well, I’ve never seen anyone use REW any other way. Of course there are countless thousands of REW users out there, so I don’t pretend to have the last word in the topic! :D


...other than the low quality of the integrated sound card's input/mic channel?
The general consensus these days is that the audio output from the headphone jack of most late-model laptops is extremely linear, but I’ve heard nothing about the mic inputs one way or another. Even if they are wonderfully flat, a computer’s mic input does not have the phantom power that measurement mics require, so you need an outboard pre amp anyway. Which puts us right back at square one: If you need a mic pre amp you might as well just get a USB audio interface, right?

Regards,
Wayne
 
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