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|4th November 2008, 07:41 PM||#1|
Join Date: Dec 2004
Location: Finland, Helsinki
L-PAD related problem with SoundEasy
I could need some help with a L-Pad attenuation.
First of all, I'm using M-Audio FireWire 410 soundcard and a consender mic with sesitivity of 5.6mV/Pa/1kHz.
Normally when I make measurements, I naturally use the front mic input for my microphone. I have to put the gain level to about 3/4 to 4/5 and use "add 15-20dB" in the SE to get correct SPL levels shown. In these measurements I use the back input for the "ref" level taken from the amplifier output. In this case I use the normal l-pad adviced by John K (Music&Design) which has 47K series resistor and 22K parallel. This works just fine (althouh the level is quite low).
But now I want to use the "absolute SPL level configuration" adviced also by John K, and this requires of taking signal straight from amplifier output to the mic input (with pad) to fine tune volume/gain levels to formerly assigned levels to achieve correct SPL.
But here is where I run to problems. With the normal L-Pad I use, the signal is WAY too high with proper gain level. The m-audio has a "pad" button which should attenuate the level 20dB but this isn't enough.
I don't know the amplifier output impedance, the mic input impedance, the required attenuation or the right l pad resistor values. How should I determine the right values? I bought few potentiometers so I could try to find proper values, but I've got absolutely no idea the ratio of the two resistors.
Could someone help with this?
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