# Squealing feedback noise when setting levels



## hifisponge (Nov 20, 2007)

I have a few questions / problems related to setting levels. The first is that I was taking some measurements last night and while adjusting the mic input levels up I would get a squealing feedback noise that you hear when a mic is too close to the speakers. The problem is that if I don't push the mic input up the levels are too low. If I set the mic input just below the level that feedback occurs, I can still hear a bit of feedback at the end of the measurement tone. Is this corrupting the measurement? What am I doing wrong?

My second question is that I really don't understand how to set the levels and calibrate the SPL reading. If I set the volume on my prepro so that the pink noise generated by REW is at 75 dB on my RS SPL meter, the level check always comes back too low. This is why I was increasing the mic input level to help get the level in the green. Increasing the mic input up doesn't get the levels all the way in the green before feedback sets in though, so I have to increase the volume on the prepro to about 78 dB. Do I enter 78 dB into the SPL calibration field? Am I doing this right? 

I also noticed that the mic is live the entire time I'm using REW (if I speak into it I can hear my voice through my sound system). Is this normal?

Thanks in advance for any help you can provide.

- Tim


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## thewire (Jun 28, 2007)

hifisponge said:


> I have a few questions / problems related to setting levels. The first is that I was taking some measurements last night and while adjusting the mic input levels up I would get a squealing feedback noise that you hear when a mic is too close to the speakers. The problem is that if I don't push the mic input up the levels are too low. If I set the mic input just below the level that feedback occurs, I can still hear a bit of feedback at the end of the measurement tone. Is this corrupting the measurement? What am I doing wrong?


What sound card are you using? If you are installing the drivers into a different USB port with an external sound card for example the settings may need to be redone. Do you have monitoring enabled? You will want to disable the playback (not recording) of the mic by checking the mute button in your mixer. If that does not work take the input that REW uses (right) and move the slider for left and right of the mic input in the recording settings of your soundcard to to the right side so that the mic input is only coming into the right. Let us know if that helps or not. 



> My second question is that I really don't understand how to set the levels and calibrate the SPL reading. If I set the volume on my prepro so that the pink noise generated by REW is at 75 dB on my RS SPL meter, the level check always comes back too low. This is why I was increasing the mic input level to help get the level in the green. Increasing the mic input up doesn't get the levels all the way in the green before feedback sets in though, so I have to increase the volume on the prepro to about 78 dB. Do I enter 78 dB into the SPL calibration field? Am I doing this right?


I can't answer that one. I think my own measurements could be suspect but I also get 78dB target in REW and a 75dB calibration on the pre/pro. Could be analog related.:huh: 



> I also noticed that the mic is live the entire time I'm using REW (if I speak into it I can hear my voice through my sound system). Is this normal?


Need to fix that.


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## brucek (Apr 11, 2006)

> The first is that I was taking some measurements last night and while adjusting the mic input levels up I would get a squealing feedback noise that you hear when a mic is too close to the speakers.


Turn off the monitoring feature in the soundcard.

brucek


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## hifisponge (Nov 20, 2007)

Thanks guys. It was just the monitoring feature that I missed. I'm using the M-Audio Mobile Pre and didn't know that there was a separate preferences function that appears when the pre is connected.

All is well. 

Thanks again.

Oh and now I can set the levels within .5dB so the SPL cal now makes sense.


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## hrpschrd (Sep 16, 2008)

How exactly do you turn off the monitoring feature in the sound card? I have an MP3+ sound card with similar symptoms (see thread below on "Check Levels inconsistent").


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## hifisponge (Nov 20, 2007)

hrpschrd said:


> How exactly do you turn off the monitoring feature in the sound card? I have an MP3+ sound card with similar symptoms (see thread below on "Check Levels inconsistent").


I had to consult the owners manual for the sound card I am using. It pointed me to a sound card preferences function that I had overlooked because it only shows when the card is plugged in.

You might want to go to the manufacturer's web site to see if they have a PDF of your sound card manual.


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## brucek (Apr 11, 2006)

> How exactly do you turn off the monitoring feature in the sound card? I have an MP3+ sound card with similar symptoms


If you can't find it, you can go directly to Windows Mixer and turn it off by muting the Line-in of the Playback Mixer (in the Recording Mixer it should be enabled).
Double click the speaker icon in your desktop system tray to find the mixer or go to the control panel.

brucek


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