# Calibrating Sound card



## gmizrahi (Jun 23, 2011)

Hi, I am a new user of the program and am trying to follow the instrctions in the preferences to calibrate the sound card. In instructions give regarding making an external loopback connetion is not clear. I do have line-in my my sound card. My question is what does it mean to make an external connection (use 3.5mm cable from line-in to which output?)


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## JohnM (Apr 11, 2006)

Connect to the same output you will use for measurement, usually a speakers or headphone output. On cards that have multi-channel outputs it would usually be the front left/right output.


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## gmizrahi (Jun 23, 2011)

JohnM said:


> Connect to the same output you will use for measurement, usually a speakers or headphone output. On cards that have multi-channel outputs it would usually be the front left/right output.


Thanks for your help John. But I still don't think I got it right. You see, my computer is connected to my receiver via hdmi. So here is my set up: The video card has dvi. So, to get the audio through DVI my video card in connected via interanl cable spdif from the motherboard to the video card. The back of the computer has several audio connections including spdif. Please let me know if you need to see photos of the back of the computer. Please help.


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## gmizrahi (Jun 23, 2011)

JohnM said:


> Connect to the same output you will use for measurement, usually a speakers or headphone output. On cards that have multi-channel outputs it would usually be the front left/right output.


The output that I am going to use for measurement is the HDMI. I first connected my line-in jack to speakers jack, and was able to calibrate the soundcard just fine. However, soundcard now is calibrated with the speakers jack and not hdmi. So when I try to do a measurement, I get a "very low signal level is measured" 

I must say I am getting increasignly frustrated. I have laready spent 6 hours trying to learn and test the calibration, with no success. Please, please help!!!


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## JohnM (Apr 11, 2006)

gmizrahi said:


> I first connected my line-in jack to speakers jack, and was able to calibrate the soundcard just fine.


That's fine, and you can check the calibration by doing the same again just to confirm the cal file is OK and you get a flat line using the speakers output and line in.



> However, soundcard now is calibrated with the speakers jack and not hdmi. So when I try to do a measurement, I get a "very low signal level is measured"


Do you hear the sweep playing when you try to make a measurement? You need to re-select the HDMI output if that is what you are using. You could also hook the speakers output to an unused input on your receiver and continue to use the speakers output, as you did during the soundcard calibration.

If you hear the sweep OK, look at the input side. Are you using an SPL meter or a mic? How have you connected it to the line in?


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## gmizrahi (Jun 23, 2011)

Ok. first things first. Here is an attachment of the sound card calibration test. Again, this is line-in to speakers using 3.5mm cable. Is that correct?


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## JohnM (Apr 11, 2006)

Yes, that is OK. Little bit of mains hum pick up (the spikes at 60/180/300/420Hz) that might be reduced by re-positioning the loopback cable (easiest way to do that is to watch the RTA screen while moving the cable, but that is probably a complication you can do without just now ).


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## gmizrahi (Jun 23, 2011)

Ok then. That's a progress. I have readjusted a bit (see attached)

I also ran a measurement test while still in a loopback( Please see attached)

Next, I changed the playback device to hdmi, selected c weighting and selected RS SPL as my calibration file. Then, I adjusted my reciever volume until I saw 75 on the SPL meter.

Next, I calibrated my SPL.

Then I ran a measurement. got that error message again that it's too low (see attached


I do hear the sweep playing through my speakers when I change the playback device to hdmi. Do I still need to connect the speaker jack to my receiver? (I'm assuming 3.5mm to rca?) 

I have the RS SPL meter connected to the line-in jack in my computer. I dowloaded the SPL calibration file and calibrated my SPL.


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## gmizrahi (Jun 23, 2011)

here is the results of a s measurement that was too low


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## JohnM (Apr 11, 2006)

Untick the phase trace, that's not needed. 

One possibility is that the left channel has been selected for measurement but the meter is connected to the right channel, or vice versa. You wouldn't see that during soundcard cal as your loopback probably links both channels through. Make sure the channel selected as the input on the Soundcard preferences is the same input that you see reacting on the Levels meters when you try and make a measurement or speak into the SPL meter.


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## gmizrahi (Jun 23, 2011)

I tried changing left/right but it doesn't affact the error message. Here is another measurement(phase off) with that error message


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## JohnM (Apr 11, 2006)

Looks like noise pickup rather than an actual signal. 

What range is the SPL meter set to? 
What approximate levels/readings does the meter show during the measurement?
What is the REW "Headroom" figure at the end of the measurement?
Click the Levels button to bring up the level meters, what level is shown in the figure at the bottom of the left and right meters when it is quiet in the room, and do the levels change on either input when you speak into the SPL meter?


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## gmizrahi (Jun 23, 2011)

JohnM said:


> Looks like noise pickup rather than an actual signal.
> 
> What range is the SPL meter set to?
> What approximate levels/readings does the meter show during the measurement?
> ...



John, the SPL meter is set to 80. 
During measurement, the highest reading was around 87
Headroom figure is 66.8
level shows 78 for the right with slight flactuations and for left it flactuates bewteen 66 and 75 (this cannot possible be correct as the SPM meter show only 58). They don't seem to change as I speak to the microphone.


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## JohnM (Apr 11, 2006)

gmizrahi said:


> Headroom figure is 66.8
> level shows 78 for the right with slight flactuations and for left it flactuates bewteen 66 and 75 (this cannot possible be correct as the SPM meter show only 58). They don't seem to change as I speak to the microphone.


These two basically say that REW is not getting any signal from the SPL meter. You get 75-ish dB levels as a result of the SPL meter calibration, when REW was told "the level you are seeing just now is 75dB", even though what it was seeing was probably not much of anything.

The meter is connected to the same Line In you used for the soundcard calibration, correct? We know from the soundcard cal that REW can see signals from that input OK, so that suggests the problem is in the connection from the SPL meter's RCA output to the soundcard's Line In. You need a cable that has a stereo 3.5mm jack on one end and two RCA plugs on the other to connect the meter to the soundcard (one of the RCAs is not used), is that what you are using?


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## gmizrahi (Jun 23, 2011)

JohnM said:


> These two basically say that REW is not getting any signal from the SPL meter. You get 75-ish dB levels as a result of the SPL meter calibration, when REW was told "the level you are seeing just now is 75dB", even though what it was seeing was probably not much of anything.
> 
> The meter is connected to the same Line In you used for the soundcard calibration, correct? We know from the soundcard cal that REW can see signals from that input OK, so that suggests the problem is in the connection from the SPL meter's RCA output to the soundcard's Line In. You need a cable that has a stereo 3.5mm jack on one end and two RCA plugs on the other to connect the meter to the soundcard (one of the RCAs is not used), is that what you are using?


ok John. I know what I was doing wrong. I was not using 3.5mm to rca. I wa using the same 3.5mm to 3.5mm. Anyway, I got my first reading. Is that correct? I just need to learn how to interpret..


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## JohnM (Apr 11, 2006)

That's more like it 

See the posting a graph sticky for tips on how to present the measurement results.


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## gmizrahi (Jun 23, 2011)

JohnM said:


> That's more like it
> 
> See the posting a graph sticky for tips on how to present the measurement results.


Thanks so much for your help and patience. I know new users can be a pain. -


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## JohnM (Apr 11, 2006)

gmizrahi said:


> I know new users can be a pain. -


Not at all, we're here to help - there is a lot to get to grips with when you are getting started, but it soon becomes familiar.


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## gmizrahi (Jun 23, 2011)

John,

I got a new Sub(Sumbersive Seaton Aduio) and recalibrated my Denon 4311 with Audessey. I recalibrated Rew with the sound card(I don't know why). This measurement was done with 1/24 smooting and audessey xt32 on and Dynamic Volume on day. Also, I included a waterfall study for your comment. You can see the soundcard and mic test are significantly lower then the measurement reading. The previous reading had the soundcard and mic test at around 75db. Is the soundcard and mic test look normal? Am I doing something wrong here? 


Also, another question that I am not sure if you can help. Audessey set my speakers as follows:

Sub 68db
L-74
R-73
SR-73
SL-72
SBL-71
SBR-72

Do I need to incease the sub level?


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## _gl (Jun 23, 2011)

A related Q - I want to calibrate my 1616m, but I'm using a phantom-powered mic input for the sweeps, so how do I calibrate it? I can't just connect the line-level output to the mic input as it's too sensitive, right? The same connector also has a line level input, but do I really need to go through the mic preamp to get an accurate calibration?


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## JohnM (Apr 11, 2006)

gmizrahi said:


> You can see the soundcard and mic test are significantly lower then the measurement reading. The previous reading had the soundcard and mic test at around 75db. Is the soundcard and mic test look normal? Am I doing something wrong here?


The cal traces are drawn across the middle of the graph, whatever level that happens to be at, so that they are always visible. The vertical span on that graph is very broad, try setting the range to 45dB at the bottom and 105dB at the top.



> Do I need to incease the sub level?


The low end looks high if anything, doesn't seem to need more level.


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## JohnM (Apr 11, 2006)

_gl said:


> A related Q - I want to calibrate my 1616m, but I'm using a phantom-powered mic input for the sweeps, so how do I calibrate it? I can't just connect the line-level output to the mic input as it's too sensitive, right? The same connector also has a line level input, but do I really need to go through the mic preamp to get an accurate calibration?


For ultimate accuracy you could use a passive attenuator in the loop and drive the mic input, but in practice most soundcard line inputs and outputs are very flat and only roll off below the point we are interested in. The soundcard calibration is as much about making sure there is no unwanted feedback (monitoring) set up in the mixer as it is checking the response, using the line level input is fine.


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## gmizrahi (Jun 23, 2011)

Thanks John. That solved the problem.


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## _gl (Jun 23, 2011)

JohnM said:


> For ultimate accuracy you could use a passive attenuator in the loop and drive the mic input, but in practice most soundcard line inputs and outputs are very flat and only roll off below the point we are interested in.


Got it, thanks John.


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## EarlK (Jan 1, 2010)

_gl said:


> A related Q - I want to calibrate my 1616m, but I'm using a phantom-powered mic input for the sweeps, so how do I calibrate it? I can't just connect the line-level output to the mic input as it's too sensitive, right? The same connector also has a line level input, but do I really need to go through the mic preamp to get an accurate calibration?



FWIW, I do include any mic preamp within a loopback calibration of any soundcard ( including external audio consoles , if used ).

Simply turn off the phantom power & then turn the preamps gain down until that output signal from REW doesn't overload the front-end of said preamp .


<> EarlK


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## _gl (Jun 23, 2011)

EarlK said:


> Simply turn off the phantom power & then turn the preamps gain down until that output signal from REW doesn't overload the front-end of said preamp .


Thanks EarlK, I'll give that a try.


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