# Very Low Level on Calibrated Mic, Please Help...



## SandmanX (Sep 20, 2006)

Hi Folks,

I am having problems getting an accurate reading due to low input levels.
I am doing some speaker testing with REW. For a soundcard I am using the Creative Soundblaster Live External 24 as recommended by this site. I am using the EMM8 electret condenser microphone and
a MP-1r microphone pre-amplifier from rivesaudio dot com

I follow the instructions in the help section and still the same occurs. To get an SPL reading I use the Radio Shack Digital SPL Meter and adjust the level to 75 db using the Creative mixer. I have the mic pre-amp set to full volume and everything else as well and I keep getting a -36 db reading on the input of REW and a warning message evertime I run a sweep.

Any thoughts?

Thanks
Ruben


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## brucek (Apr 11, 2006)

> I keep getting a -36 db reading on the input of REW


Are you using a stereo plug on the input line-in of the sound card? and if so, are you selecting the correct channel?



> I am using the EMM8 electret condenser microphone and a MP-1r microphone pre-amplifier from rivesaudio dot com


Do you have a calibration file for this mic or is it perfectly flat?

brucek


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## SandmanX (Sep 20, 2006)

brucek said:


> Are you using a stereo plug on the input line-in of the sound card? and if so, are you selecting the correct channel?
> 
> 
> Do you have a calibration file for this mic or is it perfectly flat?
> ...


Hi Brucek,

The the soundcard input wire is a mono 1/8" jack that connects to the RCA output of the mic preamp.
I tried using the left and right channel selection in the REW input and only one channel has a signal coming in which is the one I am currently using with the low level.

The Mic comes with a calibration file which I loaded into REW before I did anything else.

Thanks
Ruben


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## brucek (Apr 11, 2006)

> The the soundcard input wire is a mono 1/8" jack


That has to be a stereo plug because the soundcards jack is a stereo jack.
You only use one channel of the plug, but it still has to be stereo.

You need one of these two types of adapters. I like the wired one because the other is so bulky. They are stereo 1/8" to two channels split.


















Get one of these and we'll carry on from there. 

brucek


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## deadkenny64 (Sep 25, 2006)

I am using a stereo adapter with a RS meter as the mic with the same USB sound card and got the same error message. I switched the meter from 80db to 70db and got it to take after 2 more tries. It seems to be just barely enough signal on the line in to work with all sliders maxed. When I was using my laptop sound card (mic input) it seemed to have plenty of signal level.


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## brucek (Apr 11, 2006)

> When I was using my laptop sound card (mic input) it seemed to have plenty of signal level.


Mic inputs are unsuitable to use with REW....


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## JohnM (Apr 11, 2006)

SandmanX said:


> For a soundcard I am using the Creative Soundblaster Live External 24 as recommended by this site. I am using the EMM8 electret condenser microphone and
> a MP-1r microphone pre-amplifier


That setup works well, though the MP-1r produces a bit of noise at very low frequencies. Set the Input Volume to 1.000, to set the gain on the MP-1r play a speaker cal signal at 75dB SPL and aim for around -20dB rms input level on REW (it's easier to set the levels with speaker cal than sub cal) or look for the -10dBV LED on the MP-1r to start flickering - should find the level control is at about 2 or 3 o'clock.



deadkenny64 said:


> I am using a stereo adapter with a RS meter as the mic with the same USB sound card and got the same error message. I switched the meter from 80db to 70db and got it to take after 2 more tries. It seems to be just barely enough signal on the line in to work with all sliders maxed.


Something is wrong in the setup, with the SB Live 24-bit External and the Line In/Mic-In slider set to full (1.000) you should see around -21dB rms with the RS meter set to the 80dB range when a 75dB SPL cal signal is playing.


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