# What Does Level Too Low Mean ?



## rogerv (Nov 8, 2009)

Hi Everyone,

It's been a while since I've posted in here. Over the past couple of weeks, I've been using REW to try and dial in my new sub (HSU VTF3 Mark IV). My first go around with REW was a couple of years ago with a different HSU sub (TN1220 HO). I'm making progress, and the system is really starting to sound good. Here's the equipment set up that I'm using for measurements and equalization:

Behrenger 502
Dayton Audio EMM-6 microphone with calibration file from Cross Spectrum
Windows 8 laptop interfacing to a Creative X-FI external sound card.
Behrenger 1124P

There's always been about REW that I don't understand. :scratch: It cropped in the past and has shown up up again, so I thought I'd ask. When I do a measurement, I go through all of the preliminary steps to calibrate the REW SPL to match my Radio Shack meter. Next I click make a measurement and "Check Levels". I typically get a message indicating the "level is too low". How much "too low" seems to vary form session to session. Over the past couple of sessions, this level seems to be getting farther and farther away from the recommended levels and I don't know what's going on. 

Today it said -65 DB. When I look at my Radio Shack meter while this check level process is going on, it shows 85 DB. So, I've got plenty of sound coming out of the speakers. Needless to say I'm confused about what the "level is low" message really means and the best way to try and fix this. The message tells me to check levels and connections. I've got 4-5 places along the way that I can change levels (Microphone pre-amp, Operating System Input and Output levels for the sound card, a large dial on the sound card, Level db FS setting on REW, the Receiver itself and the sub's amp.) I've fiddled with some of these and found that when I increase some of these settings to try and make this message go away, I can hear audible noise through the speakers. So, right now, I'm just kind of dazed and confused about what's the best way to resolve this problem. If I ignore the message, the measurements seem to look reasonable.

I hope that's enough info. Let me know if there's anything else that would be helpful.

Thanks in advance for any responses.

Rog


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## JohnM (Apr 11, 2006)

The problem is in the input path rather than the output path. It is plenty loud enough in the room, 85 dB is more than you need, but the signal that REW is picking up is low, so check the volume settings along the input path.


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## Wayne A. Pflughaupt (Apr 13, 2006)

rogerv said:


> I've got 4-5 places along the way that I can change levels (Microphone pre-amp, Operating System Input and Output levels for the sound card, a large dial on the sound card, Level db FS setting on REW, the Receiver itself and the sub's amp.) I've fiddled with some of these and found that when I increase some of these settings to try and make this message go away, I can hear audible noise through the speakers.


Hey Roger,

Based on what you said about the noise problem, I’d say John nailed it: You most likely have an input signal issue because of improper gain settings on the Behringer 501 - what’s known as “gain structure” in the pro audio world. 

Proper gain structure begins right up front in the signal chain. That’s what the “trim” knob the Behringer has for the Channel 1 input is for (the channel you have the mic plugged into). The situation is that the different sources that could be plugged into the Channel 1 input potentially have different signal strength. For example, a mic vs. a guitar vs. something like an iPod. The variance in the native signal levels from sources such as these can be pretty extreme. 

The idea is to use the input gain control to maximize the source’s signal-to-noise properties coming into the mixer. If the input gain is set too low for the source (mic, guitar, etc.), then the mixer’s output stage (“Main Mix”) must be drastically elevated to compensate. _This introduces noise._ Alternately, the input stage of the next component in the signal chain must be increased – again, drastically - to compensate. This also increases noise. 

With that background it should be easy to understand the following procedure. Here’s what you need to do.

To maximize the mic and pre-amp’s signal-to-noise properties, we want to get the input level as high as possible without clipping. With the mic plugged into Channel 1 of the Behringer with a standard XLR-to-XLR mic cable, lightly tap on the mic’s element and increase the Trim knob until you see the clip light come on. Then, decrease the Trim knob just enough to make the clip light go out. You have now properly matched the mic’s signal to the pre-amp.

Next, we want to get an optimal signal to the mixer’s output stage. Start with both the Channel 1 Level and Main Mix knobs at 12:00. Tap on the mic element again, and increase the Channel 1 Level knob until the LED meter above the Main Mix knob lights up at 0 (the top green LEDs), or perhaps just barely hitting 6 (the yellow LEDs). I wouldn’t turn the Channel 1 knob higher than about 3:00, however. If you’re still not getting enough signal on the meters at that point, increase the Main Mix knob until the meters are hitting the right level. 

Anyway you cut it, adjusting these two knobs you should have no problem getting the LED meter up to 0 or 6. When that happens, you should be in good shape. Now you can run REWs input level routine and adjust the software levels as instructed by the program. 

If you still have problems, try this: Run the REW signal through your speakers (e.g. the same thing you did to get the 85 dB SPL meter reading you mentioned), and increase the Trim knob until you see the clip light, then turn it down until the clip light goes out. It’s possible that the signal from the speakers is lower than what we got with the tap-the-element exercise, and this will compensate for the difference. 

Anyway, this should get up and running. Let us know how it works out, or if you have any more problems.

Regards, 
Wayne


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## rogerv (Nov 8, 2009)

Wayne,

Thanks for your detailed reply. John was right, and I had a problem in the input side of the signal chain. Your explanation of how to set up the Behrenger was most helpful. I'm making progress on getting the noise out of the system and getting the level too low messages to go away. I do have some questions, though as well as some additional things that I learned that might be useful for others who read about this.

First the questions. On my Behrenger my Channel 1 dials I don't have anything called Trim. On mine, the top most dial is labeled "GAIN", and I'm guessing that's the same as Trim. Here's a picture of how they're labeled on my version: 









The settings shown are the most recent ones that I've used. I also have the main mix knob set at 3 o'clock, which is higher than when I started. 
I don't have my microphone attached to an XLR cable. Instead it's plugged directly into the pre-amp. I put the whole works on top of a cardboard box on my listening chair, and that seems to put the microphone at head height. Does the direct connection make a difference ?

Here are some other things that I learned during this exercise. Maybe someone else can benefit from this. 

Your description of Gain Structure made me realize that I have several other places along the signal path that needed to be properly balanced in addition to the input and output sides of the Behrenger. As it turned out, I had some imbalances in the sound card settings that got the levels o.k., but introduced noise. Thinking about balancing input and output gains for the sound card helped me get things balanced out better. On my sound card, I have settings for both "Recording Devices" and "Playback Devices" . Here are high level screen shots for both:

















When you drill down into each of these, you get level settings that affect the Gain Structure through the sound card. Following are screen shots for the detailed settings for Recording and Playback:

















I'm not completely sure about why Creative Labs put Line level adjustments in both the Line In and Speaker settings dialogues. Based on trial and error testing, I do know that they both have an effect on what REW reports, and on the amount of noise that I hear. Prior to this exercise, I made adjustments only to the Line In / Mic In settings on the recording device, and didn't do much of anything with the settings on the Speaker Properties dialog. I believe that the Speaker Properties dialog represents the Output Side of the sound card (similar to what you described for the Behrenger). 

In addition to these properties, the Sound Card has a large dial on it that also can affect the overall Gain Structure (and noise level). I don't know if that's similar to the Main Mix setting on the Behrenger or not, but it is another piece in the overall signal chain that I need to take into account.

What I've been doing is to adjust the various pieces of the signal chain to get as much gain as possible without introducing additional noise. I do still get some noise that I can hear from a couple of feet away from the speakers, but it's not as bad as before. My check levels do pass now, so I'm on the right track. The only thing that I've noticed is that the "max db level" [can't remember exactly what it's called] is lower now than previously, topping out around 92-98 DB, which seems low. I think with a little more fiddling I should be able to get everything balanced out correctly.

Thanks again for your help. There's a lot more to this part of the process than I realized, and I appreciate the help. I'll post some graphs in the future for discussion when I'm a little farther along. I'm getting close on that part, but I'm not there yet.

Regards,

Rog


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## JohnM (Apr 11, 2006)

On the speaker properties you have to set line-in/mic-in level to zero (click the speaker icon to mute it), it routes the signal from the mic back out to the speakers which creates a feedback loop.


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## rogerv (Nov 8, 2009)

John,

:thankyou:

That was the final piece. I muted this setting and all the noise is gone, and the level check works perfectly ! 

Hopefully this thread will have some value for someone else in the future.

Regards, 

Rog


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## Wayne A. Pflughaupt (Apr 13, 2006)

rogerv said:


> On my Behringer my Channel 1 dials I don't have anything called Trim. On mine, the top most dial is labeled "GAIN", and I'm guessing that's the same as Trim.


 Yes, it’s the same thing. I was going by the picture on Behringer’s web site, which shows that knob labeled “Trim.” I guess they can’t make up their minds how to label it. :huh:



> I don't have my microphone attached to an XLR cable. Instead it's plugged directly into the pre-amp. I put the whole works on top of a cardboard box on my listening chair, and that seems to put the microphone at head height. Does the direct connection make a difference?


 No. I was just covering the bases to make sure you weren’t doing something off-the-wall like plugging the mic into the 1/4" input. You can’t get anything that way because the phantom power (that the mic requires) only works from the XLR input. However, using a mic cable would give you better mic placement / orientation flexibility, especially with the addition of a mic stand.

Regards, 
Wayne


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