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Discussion Starter #1
Hello.

Ive got an HTPC with and ATI grapichcard.
I use the HDMI out, both for audio and video.

I got built in sound card, with microphone in.

Is it possible to calibrate my sound card(ATi grapichcard) ?

Ive also have an SPL meeter (unknown brand) that Ive hocked up to my computer, and that is working.
 

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I got built in sound card, with microphone in.
You require a line-in. Mic-in is not suitable.

Ive also have an SPL meeter (unknown brand)
You require a known brand with a calibration file, such as the Radio Shack or Galaxy meter.

Is it possible to calibrate my sound card(ATi grapichcard)
Yes, if it has a line-out and line-in.

brucek
 

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Discussion Starter #3
Thank you for the answer.

On the sound card(grapich) I use I only got HDMI out, with both sound and picture.

But on my motherboard I got line in.

Is it possible to connect like this:

Ati grapich card HDMI out -> Reciever -> Preout speaker on the reciever(Left or right?) -> Line in (motherboard sound card)


Ok, Guess I have to buy Radioshack. Is what is the best one, analoge or digital?


PS, sorry for my bad english, its not my native language.
 

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Is it possible to connect like this:
Ati grapich card HDMI out -> Reciever -> Preout speaker on the reciever(Left or right?) -> Line in (motherboard sound card)
Yes, if REW recognizes both the output and input you propose, and you are aware that you are assuming that the receivers line-in and preout are perfectly flat. If they are not you will introduce error into the soundcard calibration file.

People continually ask if digital-out is OK to use with REW. It's fine, except it can introduce errors at the extremes of the response depending on the quality of the D/A converter and line elements in the receiver used to 'pull off' this trick. The best method to use is a line-out and line-in.

I have to buy Radioshack. Is what is the best one, analoge or digital?
Doesn't matter really.

brucek
 

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Discussion Starter #5
"Yes, if REW recognizes both the output and input you propose, and you are aware that you are assuming that the receivers line-in and preout are perfectly flat. If they are not you will introduce error into the soundcard calibration file."

Ok.

But I use an amplifier. (also reciever pre out, amplifier, speakers)

So if it isnt flat on the reciever, wouldt it just fix those errors aswell? It would be like calibrating the reciever to?
 

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It would be like calibrating the reciever to?
Yes, and that is exactly what you don't want to do.

When measuring a device, the goal is to remove all the bias that the test equipment introduces. You don't want to remove the bias that the 'unit under test' offers or you defeat the purpose of testing.....

brucek
 

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Discussion Starter #8
I use my computer as HTPC, (playing music and movies with it)

Isnt it possible to apply the results of the soundcard calibration to the soundcard. (aka it alters the sound when I play music/videos trough a media center?)
 

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If you try and calibrate with a pre-out on the receiver you have to make sure the output is set as full range (or "large"), otherwise the receiver's bass management will alter the response by rolling off the low end at the sub crossover frequency (which looks like what has happened with your measurement).
 

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Discussion Starter #11 (Edited)
Oh, yeah. I forgot that. Thank you.
I`l do a new calibration when I come home.

EDIT got home now.

It looked much better now :)
At 15hz it was only 0.5dB off.
 

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Yes, and that is exactly what you don't want to do.

When measuring a device, the goal is to remove all the bias that the test equipment introduces. You don't want to remove the bias that the 'unit under test' offers or you defeat the purpose of testing.....

brucek
I know this is quite an old post and this was all before REW could use ASIO drivers and before there was more widespread usage of HDMI out to the receiver for the test tone sweeps, but I wanted to verify brucek's comments which I still believe to be true.

First off, my situation now is I have a laptop with an HDMI output and along with REW and ASIO4all drivers, I can send the test tone sweeps to any of the speakers in my surround system. My laptop does not have a line-in but I have an external usb sound card with a line-in that I can hook up my Galaxy CM-140 SPL meter. I was looking at how to calibrate the external sound card (or at least the line-in input as that is all I am using with the sound card) but obviously I need an output to loop back into the line-in input. I have read some posts on this forum and avsforum about them using the pre-outs of their receiver to loop back into their line-in input of their sound card but as brucek said in this previous post, and with whom I agree, this does not make any sense to do this. If I am testing the output from my speakers and receiver, and my receiver has a certain bias, I would not want to remove the 'unit under test' bias (as brucek calls it) by calibrating with the receiver pre-outs. I do want to only remove the 'test equipment' bias.

Since I need an output from the 'test equipment' only for the calibration, I can only use either the external sound card output or my laptop headphone output to loop back to the line-in input of the external sound card. Now this may introduce an error due to a bias in either the external sound card output or the laptop headphone output but there is no other way to do it. Now I have reads posts from JohnM who said that in his opinion, the sound card outputs (or laptop outputs) are usually not too far off and that it is the inputs that have a lot more variation so if a sound card calibration is desired then this should work and be fairly accurate.

What do others think? Does brucek's comments make as much sense to you as it does to me and that you should avoid using the pre-outs of the receiver as it does not make "testing sense"? JohnM, how do you know that the sound card outputs are fairly linear as opposed to the inputs or is that just an educated guess?
 

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From a practical perspective there is normally no need for a soundcard calibration for SW EQ purposes. All properly functioning soundcards are very flat between 20-20k Hz. They may fall off maybe 0.5dB at 20 Hz with a normal soundcard loopback test. [Unless your SLM is calibrated it's very likely to have a larger error than that.]

Most all SWs/room SPL responses start with >10dB range before EQ. After EQ it is considered very good be within a 5dB range. Also, most everyone here makes a several dB adjustment to the LF anyway to accommodate their preference (house curve). This is why I suggest that a 0.5dB measurement error at 20Hz is trivial.

There is nothing wrong with doing a soundcard calibration if you prefer and including the AVR in the measurement is appropriate, but again the impact is normally insignificant.

You are correct that using the HDMI output and soundcard analog input makes it very difficult to do a loopback calibration that includes the entire measurement chain. So it will be a compromise no matter what you decide. From my perspective it's a trivial compromise.

If your situation is different and there is a need more accuracy it is possible to calibrate the entire measuring system in a setup like yours, but it is more a project for those that just enjoy the frustrating challenge of it.
 
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