# soundcard feedback loop



## Guest (Nov 20, 2008)

trying to calibrate my soundcard, but i get a graph that looks like the one in the help section describing a fedback loop between the output and the input. help says to disable monitoring, but i dont have any such function. i'm using the realtek high def audio that came with the pc (hp slimlne onboard intel sound). i chaged evy seting i could find, but stil the same thing - results look like a sine wave.

any ideas


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## brucek (Apr 11, 2006)

Open the Windows mixer and select Playback Mixer (as opposed to Record Mixer) and mute the Line-In. This shuts off monitoring.

brucek


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## Guest (Nov 20, 2008)

i may not follow, if i mute the line in it essentaly disables the line in volume so my input levels in rew stay at -48?


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## brucek (Apr 11, 2006)

Disable the line-in of the *Playback* Mixer. 

The line-in of the *Record* Mixer is enabled.

*PLAYBACK MIXER*







*RECORD MIXER*









brucek


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## Guest (Nov 21, 2008)

Thanks for helping me along. I'm on vista so my mixer controls do not look like the ones you posted (thanks for that - very helpful). i'm sure the controls are there somewhere i'll try to find them.

i would like to use my spdif output (since that is what is going to the stereo). is there a way to use that as a feedback to the input to calibrate the soundcard?


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## Guest (Nov 21, 2008)

figured out the spdif question - just insert the receiver in the flow i.e., spdif out to receiver, receiver tape monitor out to soundcard analog in.

Not sure if that will fix my feedback problem, but i'll give it a go when i get home


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## Guest (Nov 21, 2008)

sorry for the multiple posts. looked into the mixer question and it looks like it may be hardware/driver dependent. when i go into the properties section for my devices (both recording and playback), i only get 1 volume level adjustment. looks like i will need to get a new soundcard (probably external since i am out of slots and mine is on-board)

is soundcard calibration that big of a deal? does it warrant getting a new soundacard or will i be ok using rew without the calibration?

thanks again for all your help - it really is great to have access to people so knowledgable and helpful


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## brucek (Apr 11, 2006)

> I'm on vista so my mixer controls do not look like the ones you posted


You didn't specify you were using Vista, so I assumed XP.

Right click on the speaker icon in the desktop system tray and select devices to reveal the mixers.
Select the default analog speakers in the playback mixer and select properties and then levels tab to show the playback line-in. Mute it..

Playback Mixer








Recording Mixer












> i would like to use my spdif output............Not sure if that will fix my feedback problem, but i'll give it a go when i get home


No, REW is designed for analog input and output. The soundcard cal renders the card absolutely flat. Once the soundcard is calibrated, the mono signal from REW line-out is connected to the receiver with a Y-adapter and the receiver is set to stereo...



> is soundcard calibration that big of a deal?


Yes, it's needed. No use measuring something that's not accurate. What would be the purpose.

brucek


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## Guest (Nov 22, 2008)

thanks so much for your help. my issue is that i was using the digital output and it didn't allow for any of the additional level adjustments. switched over to the analog and there the adjustments where.

just read that i need to be doing everything in analog so i'll have to get the splitters and start over. i think i do have some problem using the spdif becuase when i run sweeps, i can here a poping sound.

thanks again for all your help.


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## thewire (Jun 28, 2007)

uslaves said:


> i think i do have some problem using the spdif becuase when i run sweeps, i can here a poping sound.


I think that means you need to adjust your buffer.


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## Guest (Dec 4, 2008)

i'm starting to loose my mind. i have connected the analog output of the soundcard to the analog input using. when i run my calibration it looks like this:
 

i've double checked that my levels are as brucek noted
 

but still the same. if i run a measurement to check what it sounds like (disconnect the loop and connect the mic and preamp) i hear poping sounds as it does the sweep. I've set the xenyx802 levels as per instructions on this site. i've upgraded my audio drivers and my bios. i'm at a loss? my computer is an hp slimline s7712 with realtek audio drivers. here is a pic of the settings
 

i'm to my wits end...not a far journey

please help.


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## brucek (Apr 11, 2006)

Are you not able to select the card in the REW settings page?

Do you show proper input levels when you do the soundcard cal routine?

It sure looks like a feedback loop..

brucek


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## Guest (Dec 4, 2008)

brucek said:


> Are you not able to select the card in the REW settings page?


I left them as default per the suggestion in the help files. I'll try to manually select but wouldn't that not make a difference since I am getting sound output and input i.e., signal is there, so it must be selecting the proper device?



brucek said:


> Do you show proper input levels when you do the soundcard cal routine?


Yes (only on the one channel connected). the output and left input are both approx -10db



brucek said:


> It sure looks like a feedback loop..


Textbook. I just can't figure out how to kill it. I'm debating getting an outboard soundcard but dont want to spend the money if I dont have to - and if I still had the loop with the outboard card I'd loose my mind.


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## JohnM (Apr 11, 2006)

The problem is more likely the pops than a feedback loop. If you cannot get clean playback of a sine signal using the REW signal generator you will not be able to make measurements. Make sure the PC is running at full performance, no other applications running, wireless disabled.


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## Guest (Dec 4, 2008)

ok, i'm bugging out. thought i might have a soundcard issue so i bought the little beringer uca202. hooked it up, but still same problem. thought it might be the pc so i switched to my laptop. viola, got a good soundcard calibration, but then things went wrong again.

here is the soundcard calibration that i ran about 10 times with the same approx results
 
then i ran a full sweep measurement and got this 
 

ran it over and over with the same results. if i run a sine wave it sounds solid, no poping and when i run the sweep it sounds smooth. is there some weird phase cacelation going on or are my settings out wack? i'm so confused


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## brucek (Apr 11, 2006)

hehe, everything looks fine now. 

Let me give you some tips.

When you measure full range (as opposed to sub measurements up to 200Hz), then you will get comb filtering. These are reflections that make it difficult to see the underlying trend of the response, and is perfectly normal. To see the signal properly you turn on 1/3 octave smoothing (selectable in the left REW panel). Don't use smoothing for sub measurements, but certainly turn it on for full range.

For subwoofers, always use the standard Vertical graph axis of (45dB - 105dB) and the Horizontal graph axis of (15Hz - 200Hz) using the Graph Limits button in the top right corner of REW.
For full range, use the standard Vertical graph axis of (45dB - 105dB) and the Horizontal graph axis of (15Hz - upper limits you desire, i.e. 20KHZ - certainly no higher than your soundcard can extend).
For full range, as indicated above, enable smoothing to eliminate the comb filtering. Use a 1/3 octave smoothing.

So, with that new knowledge, let's see your graph with the correct graph scale and with smoothing on.

brucek


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## Guest (Dec 4, 2008)

that makes me feel better. i'll test when i get home. 

thanks so much - i'll post how it turns out


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